bq24702, bq24703

SLUS553D - MAY 2003 - REVISED JULY 2005

MULTICHEMISTRY BATTERY CHARGER CONTROLLER

AND SYSTEM POWER SELECTOR

(6,60 mm x 7,90 mm)

Actual Size

www.ti.com

FEATURES

Dynamic Power Management, DPM
Minimizes Battery Charge Time

Integrated Selector Supports Battery
Conditioning and Smart Battery Learn Cycle

Zero Volt Operation

Selector Feedback Circuit Ensures
Break-Before-Make Transition

0.4% Charge Voltage Accuracy, Suitable for

Charging Li-Ion Cells

4% Charge Current Accuracy

300-kHz Integrated PWM Controller for
High-Efficiency Buck Regulation

Depleted Battery Detection and Indication to
Protect Battery From Over Discharge

20-

A Sleep Mode Current for Low Battery

Drain

24-Pin TSSOP Package and 5 mm

5 mm

QFN package (bq24703 only)

DESCRIPTION

The bq24702/bq24703 is a highly integrated battery
charge controller and selector tailored for notebook and
sub-notebook PC applications.

The bq24702/bq24703 uses dynamic power
management (DPM) to minimize battery charge time by
maximizing use of available wall-adapter power. This is
achieved by dynamically adjusting the battery charge
current based on the total system (adapter) current.

The bq24702/bq24703 uses a fixed frequency, pulse
width modulator (PWM) to accurately control battery
charge current and voltage. Charge current limits can
be programmed from a keyboard controller DAC or by
external resistor dividers from the precision 5-V,

0.6%,

externally bypassed voltage reference (VREF),
supplied by the bq24702/bq24703.

ACDET

ACPRES

ACSEL

BATDEP

SRSET
ACSET

VREF

ENABLE

BATSET

COMP

ACN

ACP

ACDRV
BATDRV
VCC
PWM
VHSP
ALARM
VS
GND
SRP
SRN
IBAT
BATP

bq24702, bq24703

PW PACKAGE

(TOP VIEW)

ACSEL

ACPRES

ACDET

ACDRV

BATDRV

VCC

ACN

ACP

BATP

IBAT

TDEP

SRSET

ACSET

VREF

ENABLE

TSET

COMP

PWM

VHSP

ALARM

GND

SRP

SRN

bq24703

RHD PACKAGE

(BOTTOM VIEW)

NC - No internal connection

2003 - 2004, Texas Instruments Incorporated

Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of Texas Instruments
semiconductor products and disclaimers thereto appears at the end of this data sheet.

PRODUCTION DATA information is current as of publication date.

Products conform to specifications per the terms of Texas Instruments

standard warranty. Production processing does not necessarily include

testing of all parameters.

bq24702, bq24703

SLUS553D - MAY 2003 - REVISED JULY 2005

www.ti.com

DESCRIPTION (continued)

The battery voltage limit can be programmed by using the internal 1.196-V,

0.5% precision reference, making it

suitable for the critical charging demands of lithium-ion cells. Also, the bq24702/bq24703 provides an option to
override the precision reference and drive the error amplifier either directly from an external reference or from a
resistor divider off the 5 V supplied by the integrated circuit.

The selector function allows the manual selection of the system power source, battery or wall-adapter power. The
bq24702/bq24703 supports battery-conditioning and battery-learn cycles through the ACSEL function. The ACSEL
function allows manual selection of the battery or wall power as the main system power. It also provides autonomous
switching to the remaining source (battery or ac power) should the selected system power source terminate (refer
to Table 1 for the differences between the bq24702 and the bq24703). The bq24702/bq24703 also provides an alarm
function to indicate a depleted battery condition.

The bq24702/bq24703 PWM controller is ideally suited for operation in a buck converter for applications when the
wall-adapter voltage is greater than the battery voltage.

DISSIPATION RATINGS

0.20

0.40

0.60

0.80

1.20

1.40

1.60

MAX Pd (W) @ 500 LFM

MAX Pd (W) @ 250 LFM

MAX Pd (W) @ 150 LFM

MAX Pd (W) @ 0 LFM

JA = 89.37 C/W @ 0 LFM,

JA = 77.98 C/W @ 150 LFM,

JA = 73.93 C/W @ 250 LFM,

JA = 68.23 C/W @ 500 LFM

Maximum Power Dissipation (High K Board) - W

MAXIMUM POWER DISSIPATION

(HIGH K BOARD)

FREE-AIR TEMPERATURE

TA - Free-Air Temperature -

0.20

0.40

0.60

0.80

1.20

1.40

MAX Pd (W) @ 500 LFM

MAX Pd (W) @ 250 LFM

MAX Pd (W) @ 150 LFM

MAX Pd (W) @ 0 LFM

JA = 150.17 C/W @ 0 LFM,

JA = 110.95 C/W @ 150 LFM,

JA = 99.81 C/W @ 250 LFM,

JA = 86.03 C/W @ 500 LFM

Maximum Power Dissipation (Low K Board) - W

MAXIMUM POWER DISSIPATION

(LOW K BOARD)

FREE-AIR TEMPERATURE

TA - Free-Air Temperature -

The JEDEC low K (1s) board design used to derive this data was a 3-inch x 3-inch, two layer board with 2 ounce copper traces on top of the board.
The JEDEC high K (1s) board design used to derive this data was a 3-inch x 3-inch, multilayer board with 1 ounce internal power and ground

planes and 2 ounce copper traces on top and bottom of the board.

bq24702, bq24703

SLUS553D - MAY 2003 - REVISED JULY 2005

www.ti.com

Table 1. Available Options

CONDITION

SELECTOR OPERATION

CONDITION

-20

125

bq24702PW

bq24703RHD

Battery as Power Source

Battery removal

Automatically selects ac + alarm

Battery reinserted

Selection based on selector inputs

Adapter latched until adapter is removed or ac select
toggles.

AC as Power Source

AC removal

Automatically selects battery

AC reinserted

Selection based on selector inputs

Depleted Battery Condition

Battery as power source

Sends ALARM signal

Automatically selects ac
Sends ALARM signal

AC as power source

Sends ALARM signal

ALARM Signal Active

Depleted battery condition

When selector input is not equal to selector
output (single pulse alarm)

ABSOLUTE MAXIMUM RATINGS OVER OPERATING FREE-AIR TEMPERATURE

(unless otherwise noted)

}

Supply voltage range: VCC

-0.3 V to 30 V

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Battery voltage range: SRP, SRN

-0.3 V to 30 V

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Input voltage: ACN, ACP

-0.3 V to 30 V

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Virtual junction temperature range, T

-40

C to 125

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Maximum source/sink current VHSP

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Maximum ramp rate for V

10 V/

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Maximum sink current ACPRES, COMP, ALARM

2.5 mA

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Maximum ramp rate for V

(BAT)

10 V/

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Maximum source/sink current BATDRV

10 mA

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Maximum source/sink current ACDRV

10 mA

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Maximum source/sink current PWM

50 mA

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Maximum source/sink current pulsed ACDRV, (

10-

s rise time, 10-

s fall time, 1-ms pulse width, single pulse

) 50 mA

Maximum source current VREF

30 mA

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Maximum source current SRP

100 mA

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Maximum difference voltage SRP - SRN

30 V

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Storage temperature range T

stg

-65

C to 150

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Lead temperature (soldering, 10 seconds)

300

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Stresses beyond those listed under "absolute maximum ratings" may cause permanent damage to the device. These are stress ratings only, and

functional operation of the device at these or any other conditions beyond those indicated under "recommended operating conditions" is not
implied. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.

All voltages are with respect to ground. Currents are positive into and negative out of the specified terminals. Consult the Packaging section of

the data book for thermal limitations and considerations of the package.

bq24702, bq24703

SLUS553D - MAY 2003 - REVISED JULY 2005

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RECOMMENDED OPERATING CONDITIONS

(TA = TOPR) all voltages relative to Vss

MIN

MAX

UNIT

Supply voltage, (VCC)

Analog and PWM operation

7.0

Supply voltage, (VCC)

Selector operation

4.5

Negative ac current sense, (ACN)

7.0

Positive ac current sense, (ACP)

7.0

Negative battery current sense, (SRN)

Positive battery current sense, (SRP)

AC or adapter power detection (ACDET)

AC power indicator (ACPRES)

AC adapter power select (ACSEL)

Depleted battery level (BATDEP)

Battery charge current programming voltage (SRSET)

2.5

Charge enable (ENABLE)

External override to an internal 0.5% precision reference (BATSET)

2.5

Inverting input to the PWM comparator (COMP)

Battery charge regulation voltage measurement input to the battery--voltage gm amplifier (BATP)

Battery current differential amplifier output (IBAT)

System load voltage input pin (VS)

2.5

Depleted battery alarm output (ALARM)

Gate drive output (PWM)

VHSP

VCC

Battery power source select output (BATDRV)

AC or adapter power source selection output (ACDRV)

VHSP

VCC

ACSET

2.5

Operating free-air temperature, TA

-40

bq24702, bq24703

SLUS553D - MAY 2003 - REVISED JULY 2005

www.ti.com

ELECTRICAL CHARACTERISTICS

(-40

125

C, 7.0 VDC

VCC

28 VDC, all voltages relative to Vss) (unless otherwise specified)

Quiescent Current

PARAMETER

TEST CONDITIONS

MIN

TYP

MAX

UNIT

IDD(OP)

Total chip operating current

ACPRES = High, EN = 0

1.6

IDD(SLEEP) Total battery sleep current, ac not present

ACPRES = Low

logic interface dc characteristics

PARAMETER

TEST CONDITIONS

MIN

TYP

MAX

UNIT

VOL

Low-level output voltage (ACPRES, ALARM)

IOL = 1 mA

0.4

VIL

Low-level input voltage (ACSEL, ENABLE)

0.6

VIH

High-level input voltage (ACSEL, ENABLE)

1.8

I(SINK1)

Sink current (ACPRES)

VOL = 0.4

1.5

2.5

I(SINK2)

Sink current (ALARM)

VOL = 0.4

1.5

2.5

PWM Oscillator

PARAMETER

TEST CONDITIONS

MIN

TYP

MAX

UNIT

fOSC(PWM) Oscillator frequency

260

300

340

kHz

fOSC(PWM) Oscillator frequency

-40

125

240

300

350

kHz

Maximum duty cycle

100%

Input voltage for maximum dc (COMP)

3.8

Minimum duty cycle

Input voltage for minimum dc (COMP)

0.8

V(RAMP)

Oscillator ramp voltage (peak-to-peak)

1.85

2.15

2.30

VIK(COMP)

Internal input clamp voltage
(tracks COMP voltage for maximum dc)

3.8

4.5

IS(COMP)

Internal source current (COMP)

Error amplifier = OFF, V(COMP) = 1 V

110

140

Leakage Current

PARAMETER

TEST CONDITIONS

MIN

TYP

MAX

UNIT

IL(ACDET)

Leakage current, ACDET

V(ACDET) = 5 V

0.2

IL(SRSET)

Leakage current, SRSET

V(SRSET) = 2.5 V

0.2

IL(ACSET)

Leakage current, ACSET

V(ACSET) = 2.5 V

0.2

IL(BATDEP)

Leakage current, BATDEP

V(BATDEP) = 5 V

0.2

IL(VS)

Leakage current, VS

V(VS) = 5 V

0.2

IL(ALARM)

Leakage current, ALARM

V(ALARM) = 5 V

0.2

IL(ACSEL)

Leakage current, ACSEL

V(ACSEL) = 5 V

0.2

IL(ENABLE)

Leakage current, ENABLE

V(ENABLE) = 5 V

0.2

IL(ACPRES)

Leakage current, ACPRES

V(ACPRES) = 5 V

0.2

IL(BATP)

Leakage current, BATP

V(BATP) = 5 V

0.2

IL(BATSET)

Leakage current, BATSET

V(BATSET) = 2.5 V

0.2

bq24702, bq24703

SLUS553D - MAY 2003 - REVISED JULY 2005

www.ti.com

ELECTRICAL CHARACTERISTICS

(CONTINUED)

(-40

125

C, 7.0 VDC

VCC

28 VDC, all voltages relative to Vss) (unless otherwise specified)

Battery Current-Sense Amplifier

PARAMETER

TEST CONDITIONS

MIN

TYP

MAX

UNIT

Transconductance gain

120

175

mA/V

CMRR

Common-mode rejection ratio

See Note 1

VICR

Common-mode input (SRP, SRN)
voltage range

VCC = SRN, SRP + 2 V

I(SINK)

Sink current (COMP)

COMP = 1 V,

(SRP - SRN) = 10 mV

0.5

1.5

2.5

IIB

Input bias current (SRP), See Note 2

V(SRP) = 16 V,
(SRP - SRN) = 100 mV

SRSET = 2.5 V,
VCC = 28

110

IIB

Input bias current accuracy
(ISRP - ISRN)

(SRP - SRN) = 100 mV, SRSET= 2.5 V,
VCC = 28 V, 0

125

-3

V(SET)

Battery current programming voltage
(SRSET)

2.5

Battery current set gain

0.65 V

SRSET

2.5 V, 8 V

SRN

16 V,

See Note 3

V/V

Total battery current-sense mid-scale

SRSET = 1.25 V, TJ = 25

C, See Note 4

-5%

Total battery current-sense mid-scale
accuracy

SRSET = 1.25 V, See Note 4

-6%

Total battery current-sense full-scale

SRSET = 2.5 V, TJ = 25

C, See Note 4

-3%

Total battery current-sense full-scale
accuracy

SRSET = 2.5 V, See Note 4

-4%

NOTES: 1. Specified by design. Not production tested.

I(SRP) = I(SRN) = (V(SRSET) / 50 k

) + ((V(SRP) - V(SRN) / 3 k

)

example: If (V(SRSET) = 2.5 V) , (V(SRP) - V(SRN) = 100 mV) Then I(SRP) = I(SRN) = 83

3. I

BAT

SRSET

SENSE

4. Total battery-current set is based on the measured value of (SRP-SRN) =

m, and the calculated value of (SRP-SRN) =

C, using

the measured gain, AV.

SRSET

, Total accuracy in %

(

* D

100, I

(SRP)

(SRN)

bq24702, bq24703

SLUS553D - MAY 2003 - REVISED JULY 2005

www.ti.com

ELECTRICAL CHARACTERISTICS

(CONTINUED)

(-40

125

C, 7.0 VDC

VCC

28 VDC, all voltages relative to Vss) (unless otherwise specified)

Adapter Current-Sense Amplifier

PARAMETER

TEST CONDITIONS

MIN

TYP

MAX

UNIT

Transconductance gain

130

175

mA/V

CMRR

Common-mode rejection ratio

See Note 1

VICR

Common-mode input voltage range (ACP)

7.0

VCC

I(SINK)

Sink current (COMP)

COMP = 1 V, (ACP - ACN) = 10 mV

0.5

1.5

2.5

IIB

Input bias current (ACP, ACN)

ACP = ACN = 28 V,
VCC = 28 V, ACSET = 2.5 V

IIB

Input bias current accuracy ratio
(I(ACP), I(ACN))

ACP = ACN = 28 V, VCC = 28 V,
ACSET = 2.5 V, 0

125

-3

V(SET)

AC current programming voltage (ACSET)

2.5

AC current set gain

0.65 V

ACSET

2.5 V, 12 V

ACP

20 V,

See Note 5

24.5

25.3

26.5

V/V

Total ac current-sense mid-scale accuracy

ACSET = 1.25 V, TJ = 25

C, See Note 6

-5%

Total ac current-sense mid-scale accuracy

ACSET = 1.25 V, See Note 6

-6%

Total ac current-sense full-scale accuracy

ACSET = 2.5 V, TJ = 25

C, See Note 6

-3.5%

3.5%

Total ac current-sense full-scale accuracy

ACSET = 2.5 V, See Note 6

-4%

Battery Voltage Error Amplifier

PARAMETER

TEST CONDITIONS

MIN

TYP

MAX

UNIT

Transconductance gain

135

175

mA/V

CMRR

Common-mode rejection ratio

See Note 1

VICR

BATSET common-mode input voltage range

2.5

VIT

Internal reference override input threshold voltage

0.20

0.25

0.35

I(SINK)

Sink current COMP

COMP = 1 V,
(BATP - BATSET) = 10 mV,
BATSET = 1.25 V

0.5

1.5

2.5

TJ = 25

1.190

1.196

1.202

V(FB)

Error-amplifier precision reference voltage

TJ = 0

C to 85

1.183

1.196

1.203

V(FB)

Error-amplifier precision reference voltage

TJ = -40

C to 125

1.178

1.196

1.204

NOTE:

5. Calculation of the ac current: I

ACSET

SENSE

6. Total ac-current set accuracy is based on the measured value of (ACP-ACN) =

c, using the measured gain, AV.

ACSET

, Total accuracy in %

(

* D

100, I

(ACP)

(ACN)

bq24702, bq24703

SLUS553D - MAY 2003 - REVISED JULY 2005

www.ti.com

ELECTRICAL CHARACTERISTICS

(CONTINUED)

(-40

125

C, 7.0 VDC

VCC

28 VDC, all voltages relative to Vss) (unless otherwise specified)

Battery Current Output Amplifier

PARAMETER

TEST CONDITIONS

MIN

TYP

MAX

UNIT

G(TR)

Transfer gain

(SRP - SRN) = 5 mV, See Note 7

V/V

VI(BAT)

Battery current readback output
voltage (IBAT)

(SRP - SRN) = 5 mV, SRP = 12 V,
VCC = 18 V, TJ = 25

100

Line rejection voltage

TJ = 25

mV/V

Common-mode input range (SRP)

VO(IBAT)

Battery current output voltage range
(IBAT)

2.5

IS(O)

Output source current (IBAT)

(SRP - SRN) = 100 mV

7.1

9.4

(SRP - SRN) = 50 mV, TJ = 25

C, See Note 7

-3%

2.4%

Total battery current readback

(SRP - SRN) = 50 mV, 0

-20%

20%

Total battery current readback
full-scale accuracy

(SRP - SRN) = 100 mV, TJ = 25

C, See Note 7

-1.5%

1.2%

full-scale accuracy

(SRP - SRN) = 100 mV, 0

C < TJ < 85

-6%

8.5%

5-V Voltage Reference

PARAMETER

TEST CONDITIONS

MIN

TYP

MAX

UNIT

TJ = 25

4.985

5.013

Vref

Output voltage (VREF)

TJ = 0

C to 85

4.946

5.013

Vref

Output voltage (VREF)

TJ = 40

C to 85

4.946

5.03

TJ = -40

C to 125

4.926

5.03

Line regulation

ILOAD = 5 mA

0.1

0.37

mV/V

Load regulation

1 mA

ILOAD

5 mA

1.1

mV/mA

Short circuit current

5V REF output capacitor

Capacitance

2.2

Output capacitor equivalent resistor

ESR

1000

Half Supply Regulator

PARAMETER

TEST CONDITIONS

MIN

TYP

MAX

UNIT

V(HSP)

Voltage regulation

I(SINK) = 20 mA, VCC = 18 V

VCC - 11

VCC - 10.2

VCC - 8.5

V(HSP)

Voltage regulation

I(SINK) = 1 mA, VCC = 7 V

1.5

NOTE:

7. Battery readback transfer gain G

IBAT

(SRP

SRN)

bq24702, bq24703

SLUS553D - MAY 2003 - REVISED JULY 2005

www.ti.com

ELECTRICAL CHARACTERISTICS

(CONTINUED)

(-40

125

C, 7.0 VDC

VCC

28 VDC, all voltages relative to Vss) (unless otherwise specified)

MOSFET Gate Drive

PARAMETER

TEST CONDITIONS

MIN

TYP

MAX

UNIT

AC driver RDS(on) high

VCC = 18 V, I(ACDRV) = 1 mA

150

AC driver RDS(on) low

VCC = 18 V, I(ACDRV) = 1 mA

110

Battery driver RDS(on) high

VCC = 18 V, I(BATDRV) = 1 mA

315

600

Battery driver RDS(on) low

VCC = 18 V, I(BATDRV) = 1 mA

115

tda

Time delay from ac driver off to battery
driver on

ACSEL 2.4 V

0.2 V

1.2

tdb

Time delay from battery driver off to ac
driver on

ACSEL 0.2 V

2.4 V

2.4

3.3

VOH

PWM driver high-level output voltage

IO = -10 mA, VCC = 18 V

VCC -0.18 VCC -0.09

VOH

PWM driver high-level output voltage

IO = -50 mA, VCC = 18 V

VCC -1.2

VCC -0.8

PWM driver RDS(on) high

VOL

PWM driver low-level output voltage

IO = 10 mA, VCC = 18 V

VHSP+0.1

VHSP+0.4

VOL

PWM driver low-level output voltage

IO = 50 mA, VCC = 18 V

VHSP+0.6

VHSP+1.2

PWM driver RDS(on) low

8.5

Selector

PARAMETER

TEST CONDITIONS

MIN

TYP

MAX

UNIT

V(ACPRES)

AC presence detect voltage

1.194

1.246

1.286

V(ACPRES)

AC presence detect voltage

-40

C to 85

1.208

1.246

1.285

VIT(ACPRES) AC presence hysteresis

td(ACPRES)

Deglitch delay for adapter insertion

100

V(BATDEP)

Battery depletion ALARM trip voltage

See Note 8

1.194

1.246

1.286

V(BATDEP)

Battery depletion ALARM trip voltage

-40

C to 85

1.208

1.246

1.285

V(NOBAT)

No battery detect, switch to ACDRV

bq24702 only, See Note 8

0.869

1.144

V(NOBAT)

No battery detect, switch to ACDRV

-40

C to 85

0.880

1.118

t(BATSEL)

Battery select time (ACSEL low to BATDRV low)

VS < BATP, 50% threshold,
ACSEL 2.4 V

0.2 V

2.5

3.5

t(ACSEL)

AC select time (ACSEL high to ACDRV low)

ACSEL 0.2 V

2.4 V

2.5

3.5

V(VS)

VS voltage to enable BATDRV

BATP = 1 V

0.98

1.02

VIT(VS)

VS voltage hysteresis

VS > BATP

Zero Volt Operation

PARAMETER

TEST CONDITIONS

MIN

TYP

MAX

UNIT

rDS(on)

Static drain source on-state resistance

VCC = 7 V, TJ = 125

C, IO = 100 mA

5.3

8.7

zero volt operation threshold

BATDEP increasing

0.743

0.794

0.840

zero volt operation threshold

BATDEP decreasing

0.570

0.62

0.656

NOTES: 8. Total battery current readback accuracy is based on the measured value of VIBAT, VIBATm, and the calculated value of VIBAT,

VIBATc, using the measured value of the transfer gain, GTR.

IBATc

(SRP

SRN)

GTR

Total Accuracy in %

IBATm

IBATc

IBATm

100

9. Refer to Table 1 to determine the logic operation of the bq24702 and the bq24703.

bq24702, bq24703

SLUS553D - MAY 2003 - REVISED JULY 2005

www.ti.com

APPLICATION DIAGRAM

Open

R12

Note

R14

0.025

R13

R15

C12

SI4435DY

R18

BAS16

ACDRV

ACN

ACP

ACDET

VCC

VHSP

13 V

SRP

16V

35 V

PWM

SI4435DY

R20

SRN

Note 1

R22

R23

Note

R24

R25

Note

TDEP

R16

150pF

COMP

MBRD640CTT4

35 V

R21

Note

R19

Note

SI4435DY

BAS16

R26

100K

TDRV

SYSTEM

R27

R28

Note

Battery Plus

Adapter

VREF
7

ENABLE

ACSEL
3

ALARM

ACPRES

ENABLE

ACSEL

ALARM

ACPRES

SRSET

ACSET

R10

Note

C10

180pF

IBA

C13

1 nF

IBA

R29

GND

TSET

100 k

100

4.7

0.025

100

4.7

604 k

Connect to GND

to Disable

100 k

30 k

4.7

Note 1:

R8 Sets

Adapter Current Limit

R10 Sets Charge Current

R12

Sets

ADAPTER Current Limit

R23 Sets the Battery Depleted

Threshold

R25 Sets the Charge Regulation V

oltage

R28 Sets System Break Before Make

R19 = R21, Sets Zero V

olt Charge Current

bq24703

bq24702

Note

604 k

Note

1 Optional, See

Application

Notes

C12 For V

alue, See

Application

Notes

C8 V

alue Depends on R21 and R19, See

Application

Notes

D5, D6 Refer to the

Application

Section

PROCESSOR'S

POWER SUPPL

bq24702, bq24703

SLUS553D - MAY 2003 - REVISED JULY 2005

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BLOCK DIAGRAM

UDG-00137

VHSP

REGULATOR

VCC

VREF

VOLTAGE

REFERENCE

VREF

ACPRES

ACDET

ACPRES

HYST

LEVEL

SHIFT

PWM

LOGIC

OSC

HIGH-SIDE

DRIVE

300 kHz

ACSEL

ENABLE

VCC

VHSP

COMP

5 V

100

5 V

SRN

2 k

ACP

ACN

ACSET

VCC

CURRENT

ERROR

AMPLIFIER

BATTERY

CURRENT

ERROR

AMPLIFIER

BATTERY

VOLTAGE

ERROR

AMPLIFIER

PWM

BATP

BATSET

SRP

2 k

SRN

SRSET

0.25 V

BATTERY

SELECT

DRIVE

ADAPTER

SELECT

DRIVE

VCC

VHSP

VCC

BATDRV

BATTERY SELECT

LOGIC

AND

ANTI-CROSS

CONDUCT

NO BATTERY

COMPARATOR

GND

A=20

VCC

IBAT

SRP

SRN

ACSEL

ACPRES

SWITCH TO
BATTERY

BATDEP

DEPLETED

BATTERY

COMPARATOR

BATP

ACDRV

ACSEL

bq24702 ONLY

bq24703 ONLY

ALARM

2 V

BATDA

VTBD

Zero Volt

Charging

VACPRES

VFB

0.8 x VNOBAT

VBATDEP

bq24702, bq24703

SLUS553D - MAY 2003 - REVISED JULY 2005

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Terminal Functions

TERMINAL

NAME

bq24702

(PW)

bq24703

(QFN)

I/O

DESCRIPTION

ACDET

AC or adapter power detection

ACDRV

AC or adapter power source selection output

ACN

Negative differential input

ACP

Positive differential input

ACPRES

AC power indicator

ACSEL

AC adapter power select

ACSET

Adapter current programming voltage

ALARM

Alarm output

BATDEP

Depleted battery level

BATDRV

Battery power source select output

BATP

Battery charge regulation voltage measurement input to the battery-voltage gm amplifier

BATSET

External override to an internal precision reference

COMP

Inverting input to the PWM comparator

ENABLE

Charge enable

GND

Supply return and ground reference

IBAT

Battery current differential amplifier output

PWM

Gate drive output

SRN

Negative differential battery current sense amplifier input

SRP

I/O

Positive differential battery current sense amplifier input

SRSET

Battery charge current programming voltage

VCC

Operational supply voltage

VHSP

Voltage source to drive gates of the external MOSFETs

VREF

Precision 5-V reference

System (load) voltage input pin

bq24702, bq24703

SLUS553D - MAY 2003 - REVISED JULY 2005

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Pin Assignments

ACDET: AC or adapter power detection. This input pin is used to determine the presence of the ac adapter.
When the voltage level on the ACDET pin is less than V

ACPRES

, the bq24702/bq24703 is in sleep mode, the

PWM control is disabled, the BATDRV is driven low, and the ACDRV is driven high. This feature can be used
to automatically select battery as the system power source.

ACDRV: AC or adapter power source select output. This pin drives an external P-channel MOSFET used to
switch to the ac wall-adapter as the system power source. When the ACSEL pin is high while the voltage on
the ACDET pin is greater than V

ACPRES

, the output ACDRV pin is driven low (V

HSP

). This pin is driven high (V

)

when the ACDET is less than V

ACPRES

ACN, ACP: Negative and positive differential inputs, respectively for ac-to-dc adapter current sense resistor.

ACPRES: This open-drain output pin is used to indicate the presence of ac power. A logic high indicates there
is a valid ac input. A low indicates the loss of ac power. ACPRES is high when the voltage level on the ACDET
pin is greater than V

ACPRES

ACSEL: AC adapter power select. This input selects either the ac adapter or the battery as the power source.
A logic high selects ac power, while a logic low selects the battery.

ACSET: Adapter current programming voltage. This input sets the system current level at which dynamic power
management occurs. Adapter currents above this programmed level activate the dynamic power management
and proportionally reduce the available power to the battery.

ALARM: Depleted battery alarm output. This open-drain pin indicates that a depleted battery condition exists.
A pullup on ALARM goes high when the voltage on the BATDEP pin is below V

ACPRES

. On the bq24702, the

ALARM output also activates when the selector inputs do not match the selector state.

BATDEP: Depleted battery level. A voltage divider network from the battery to BATDEP pin is used to set the
battery voltage level at which depletion is indicated by the ALARM pin. See ALARM pin for more details. A
battery depletion is detected when BATDEP is less than V

ACPRES

. A no-battery condition is detected when the

battery voltage is < 80% of the depleted threshold. In a no-battery condition, the bq24702 automatically selects
ac as the input source. If ENABLE = 1, the PWM remains enabled.

BATDRV: Battery power source select output. This pin drives an external P-channel MOSFET used to switch
the battery as the system's power source. When the voltage level on the ACDET pin is less than V

ACPRES

, the

output of the BATDRV pin is driven low, GND. This pin is driven high (V

) when ACSEL is high and ACDET

> V

ACPRES

BATP: Battery charge regulation voltage measurement input to the battery-voltage g

amplifier. The voltage

on this pin is typically derived from a voltage divider network connected across the battery. In a voltage loop,
BATP is regulated to the V

precision reference of the battery voltage g

amplifier.

BATSET: An external override to an internal precision reference. When BATSET is > 0.25 V, the voltage level
on the BATSET pin sets the voltage charge level. When BATSET

0.25 V, an internal V

reference is

connected to the inverting input of the battery error amplifier. To ensure proper battery voltage regulation with
BATSET, BATSET must be > 1.0 V. Simply ground BATSET to use the internal reference.

COMP: The inverting input to the PWM comparator and output of the g

amplifiers. A type II compensation

network between COMP and GND is recommended.

ENABLE: Charge enable. A high on this input pin allows PWM control operation to enable charging while a low
on this pin disables and forces the PWM output to a high state. Battery charging is initiated by asserting a logic
1 on the ENABLE pin.

GND: Supply return and ground reference

IBAT: Battery current differential amplifier output. The output of this pin produces a voltage proportional to the
battery charge current. This voltage is suitable for driving an ADC input.

bq24702, bq24703

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PWM: Gate drive output pin drives the P-channel MOSFET for PWM control. The PWM control is active when
ACPRES, ACSEL, and ENABLE are high. PWM is driven low to V

HSP

and high to V

SRN, SRP: Differential amplifier inputs for battery current sense. These pins feed back the battery charge
current for PWM control. SRN is tied to the battery terminal. SRP is the source pin for zero volt operation.

SRSET: Battery charge current programmed voltage. The level on this pin sets the battery charge current limit.

VCC: Operational supply voltage.

VHSP: The VHSP pin is connected to a 1-

F capacitor (close to the pin) to provide a stable voltage source to

drive the gates of the external MOSFETs. VHSP = VCC - 10 V for VCC > 10.5 V and VHSP = VCC - 0.5 V for
VCC <10.5 V. A 13-V Zener diode should be placed between VCC and VHSP to prevent MOSFET overstress
during start-up.

VREF: Bypassed precision voltage 5-V output. It can be used to set fixed levels on the inverting inputs of any
one of the three error amplifiers if desired. The tight tolerance is suitable for charging lithium-ion batteries.

VS: System (Load) voltage input pin. The voltage on this pin indicates the system voltage in order to insure a
break before make transition when changing from ac power to battery power. The battery is protected from an
over-voltage condition by disabling the P-channel MOSFET connected to the BATDRV pin if the voltage at VS
is greater than BATP. This function can be eliminated by grounding the VS pin.

bq24702, bq24703

SLUS553D - MAY 2003 - REVISED JULY 2005

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APPLICATION INFORMATION

Programming the Thresholds

The input-referenced thresholds for battery depleted, ac detection and charge voltage are defined by
dimensioning the external dividers connected to pins BATDEP, ACDET and BATP. This calculation is simple,
and consists of assuming that when the input voltage equals the desired threshold value the voltage at the
related pin is equal to the pin internal reference voltage:

Vinput = Vpin

(1 + Kres)

where:

Vinput = Target threshold, referenced to input signal
Vpin = Internal reference(1.196 V for BATP; 1.246 V for BATDEP, ACDET)
Kres = External resistive divider gain ( for instance: R24/R25 for BATP)

When using external dividers with high absolute value the input bias currents for those pins must be included
in the threshold calculation. On the bq24702/3 the input bias currents increase the actual value for the threshold
voltage, when compared to the values calculated using the internal references and divider gain only:

Vinput = Vpin

(1+Kres) + Vbias

The increase on the threshold voltage is given by:

Vbias = Rdiv

Ipin

where:

Vbias = Voltage increase due to pin bias current
Rdiv = External resistor value for resistor connected from pin to input voltage
Ipin = Maximum pin leakage current

The effect of IB can be reduced if the resistor values are decreased.

Dynamic Power Management

The dynamic power management (DPM) feature allows a cost effective choice of an ac wall-adapter that
accommodates 90% of the system's operating-current requirements. It minimizes battery charge time by
allocating available power to charge the battery (i.e. I

BAT

= I

ADPT

- I

SYS

). If the system plus battery charge

current exceeds the adapter current limit, as shown in Figure 1, the DPM feature reduces the battery charge
current to maintain an overall input current consumption within user defined power capability of the wall-adapter.
As the system's current requirements decrease, additional current can be directed to the battery, thereby
increasing battery charge current and minimizing battery charge time.

The DPM feature is inherently designed into the PWM controller by inclusion of the three control loops,
battery-charge regulation voltage, battery-charge current, and adapter-charge current, refer to Figure 2. If any
of the three user programmed limits are reached, the corresponding control loop commands the PWM controller
to reduce duty cycle, thereby reducing the battery charge current.

bq24702, bq24703

SLUS553D - MAY 2003 - REVISED JULY 2005

www.ti.com

UDG-00113

CHARGE

MAXIMUM

CHARGE CURRENT

DYNAMIC POWER

MANAGEMENT

MAXIMUM

CHARGE CURRENT

ADAPTER CURRENT

SYSTEM CURRENT

BATTERY CHARGE CURRENT

ADAPTER CURRENT LIMIT

Figure 1. Dynamic Power Management

ACDET Operation

The ACDET function senses the loss of adequate adapter power. If the voltage on ACDET drops below the
internal V

ACPRES

reference voltage, a loss of ADAPTER power is declared and the bq24702/bq24703 switches

to battery power as the main system power. In addition, the bq24702/bq24703 shuts down its 5-V VREF and
enters a low power sleep mode.

Battery Charger Operation

The bq24702/bq24703 fixed-frequency, PWM controller is designed to provide closed-loop control of battery
charge-current (I

) based on three parameters, battery-float voltage (V

BAT

), battery-charge current, and

adapter charge current (I

ADPT

). The bq24702/bq24703 is designed primarily for control of a buck converter

using a high side P-channel MOSFET device (SW, refer to Figure 2).

The three control parameters are voltage programmable through resistor dividers from the bq24702/bq24703
precision 5-V reference, an external or internal precision reference, or directly via a DAC interface from a
keyboard controller.

Adapter and battery-charge current information is sensed and fed back to two transconductance (g

) amplifiers

via low-value-sense resistors in series with the adapter and battery respectively. Battery voltage information is
sensed through an external resistor divider and fed back from the battery to a third g

amplifier.

Precharge Operation

The precharge operation must be performed using the PWM regulator. The host can set the precharge current
externally by monitoring the ALARM pin to detect a battery depleted condition and programming SRSET voltage
to obtain the desired precharge current level.

bq24702, bq24703

SLUS553D - MAY 2003 - REVISED JULY 2005

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Zero Volt Operating

The zero volt operation is intended to provide a low current path to close open packs and protect the system
in the event of a pack cell short-circuit condition or if a short is applied to the pack terminal. It is not designed
to precharge depleted packs, as it is disabled at voltages that are not within normal pack operating range for
precharge.

If the voltage at BATDEP pin is below the zero volt operation threshold , charge is enabled (EN=HI), and ac is
selected (ACSEL=HI) the bq24702/3 enters the zero volt operation mode. When the zero volt operation mode
is on, the internal PWM is disabled, and an internal power MOSFET connects SRP to V

. The battery charge

current is limited by the filter resistor connected to SRP pin (R19). R19 must be dimensioned to withstand the
worst case power dissipation when in zero volt operation mode.

The zero volt operation mode is disabled when BATDEP is above the zero volt operation threshold, and the main
PWM loop is turned on if charge is enabled, regulating the current to the value set by SRSET voltage. To avoid
errors on the charge current both resistors on the SRP, SRN filter must have the same value. Note, however,
that R21 (connected to SRN) does not dissipate any power when in zero volt operation and can be of minimum
size.

PWM Operation

The three open collector g

amplifiers are tied to the COMP pin (refer to Figure 2), which is internally biased

up by a 100-

A constant current source. The voltage on the COMP pin is the control voltage (V

) for the PWM

comparator. The PWM comparator compares V

to the sawtooth ramp of the internally fixed 300-kHz oscillator

to provide duty cycle information for the PWM drive. The PWM drive is level-shifted to provide adequate gate
voltage levels for the external P-channel MOSFET. Refer to PWM selector switch gate drive section for gate
drive voltage levels.

UDG-00114

100

ENABLE

5 V

OSC

CLK

RAMP

ENABLE

LATCH OUT

FROM ENABLE LOGIC

PWM COMPARATOR

LEVEL

SHIFT

PWM

DRIVE

VHSP

VCC

1.25 V

BATTERY

VOLTAGE

BATTERY CHARGE

CURRENT

ADP CURRENT

COMP

ADPT

BAT

AMPLIFIERS

PWM

BATP

Figure 2. PWM Controller Block Diagram

bq24702, bq24703

SLUS553D - MAY 2003 - REVISED JULY 2005

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Softstart

Softstart is provided to ensure an orderly start-up when the PWM is enabled. When the PWM controller is
disabled (ENABLE = Low), the 100-

A current source pullup is disabled and the COMP pin is actively pulled

down to GND. Disabling the 100-

A pullup reduces current drain when the PWM is disabled. When the

bq24702/bq24703 PWM is enabled (ENABLE = High), the COMP pin is released and the 100-

A pullup is

enabled (refer to Figure 2). The voltage on the COMP pin increases as the pullup charges the external
compensation network connected to the COMP pin. As the voltage on the COMP pin increases the PWM duty
cycle increases linearly as shown in Figure 3.

Figure 3

100

VCOMP - Compensation Voltage - V

Percent Duty Cycle - %

PERCENT DUTY CYCLE

COMPENSATION VOLTAGE

1.2

1.7

2.2

2.7

3.2

As any one of the three controlling loops approaches the programmed limit, the g

amplifier begins to shunt

current away from the COMP pin. The rate of voltage rise on the COMP pin slows due to the decrease in total
current out of the pin, decreasing the rate of duty cycle increase. When the loop has reached the programmed
limit the g

amplifier shunts the entire bias current (100

A) and the duty cycle remains fixed. If any of the control

parameters tries to exceed the programmed limit, the g

amplifier shunts additional current from the COMP pin,

further reducing the PWM duty cycle until the offending parameter is brought into check.

Setting the Battery Charge Regulation Voltage

The battery charge regulation voltage is programmed through the BATSET pin, if the internal precision
reference is not used. The BATSET input is a high-impedance input that is driven by either a keyboard controller
DAC or via a resistor divider from a precision reference (see Figure 4).

The battery voltage is fed back to the g

amplifier through a resistor divider network. The battery charge

regulation voltage can be defined as:

BATTERY

(R1

)

R2)

BATSET

)

BATP

where I

BATP

= input bias current for pin BATP

(1)

bq24702, bq24703

SLUS553D - MAY 2003 - REVISED JULY 2005

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The overall accuracy of the battery charge regulation voltage is a function of the bypassed 5-V reference voltage
tolerance as well as the tolerances on R1 and R2. The precision voltage reference has a 0.5% tolerance making
it suitable for the tight battery voltage requirements of Li-ion batteries. Tolerance resistors of 0.1% are
recommended for R1 and R2 as well as any resistors used to set BATSET.

The bq24702/bq24703 provides the capability of using an internal precision voltage reference through the use
of a multiplexing scheme, refer to Figure 4, on the BATSET pin. When BATSET voltage is less than 0.25 V, an
internal reference is switched in and the BATSET pin is switched out from the g

amplifier input. When the

BATSET voltage is greater than 0.25 V, the BATSET pin voltage is switched in to the input of the g

amplifier

and the voltage reference is switched out.

NOTE:The minimum recommended BATSET is 1.0 V, if BATSET is used to set the voltage loop.

UDG-00116

(a) VBATSET < 0.25 V

(b) VBATSET > 1 V

0.25 V

BATSET

BATP

VBAT

gm AMPLIFIER

1.196 V

VREF = 5 V

COMP

0.25 V

BATSET

BATP

VBAT

gm AMPLIFIER

1.25 V

COMP

Figure 4. Battery Error Amplifier Input Multiplexing Scheme

bq24702, bq24703

SLUS553D - MAY 2003 - REVISED JULY 2005

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Programming the Battery Charge Current

The battery charge current is programmed via a voltage on the SRSET pin. This voltage can be derived from
a resistor divider from the 5-V VREF or by means of an DAC. The voltage is converted to a current source that
is used to develop a voltage drop across an internal offset resistor at one input of the SR g

amplifier. The charge

current is then a function of this voltage drop and the sense resistor (R

), refer to Figure 5.

UDG-00117

25 k

COMP

2 k

SRN

SRP

VREF

SRSET

Figure 5. Battery Charge Current Input Threshold Function

The battery charge current can be defined as:

BAT

SRSET

where V

SRSET

is the programming voltage on the SRSET pin. V

SRSET

maximum is 2.5 V.

Programming the Adapter Current

Like the battery charge current described previously, the adapter current is programmed via a voltage on the
ACSET pin. That voltage can either be from an external resistor divider from the 5-V VREF or from an external
DAC. The adapter current is defined as:

ADPT

ACSET

(2)

(3)

bq24702, bq24703

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COMPONENT SELECTION

MOSFET Selection

MOSFET selection depends on several factors, namely, gate-source voltage, input voltage, and input current.
The MOSFET must be a P-channel device capable of handling at least 15-V gate-to-source with a drain-source
breakdown of V

~ V

+1 V. The average input current can be approximated by:

(avg)

Ichg

D = Duty cycle

Ichg = Charge current

The RMS current through the MOSFET is defined as:

(RMS)

Ichg

RMS

The rise/fall times for pin PWM for the selected MOSFET should be greater than 40 nsec.

Schottky Rectifier (Freewheeling)

The freewheeling Schottky rectifier must also be selected to withstand the input voltage, V

. The average

current can be approximated from:

(avg)

Ichg

D) A

Choosing an Inductance

Low inductance values result in a steep current ramp or slope. Steeper current slopes result in the converter
operating in the discontinuous mode at a higher power level. Steeper current slopes also result in higher output
ripple current, which may require a higher number or more expensive capacitors to filter the higher ripple current.

In addition, the higher ripple current results in an error in the sensed battery current particularly at lower charging
currents. It is recommended that the ripple current not exceed 20% to 30% of full scale dc current.

BAT

Ichg

Ripple

Ripple = % Ripple allowed (Ex.: 0,2 for 20% ripple)

Too large an inductor value results in the current waveform of Q1 and D1 in Figure 2 approximating a
squarewave with an almost flat current slope on the step. In this case, the inductor is usually much larger than
necessary, which may result in an efficiency loss (higher DCR) and an area penalty.

Selecting an Output Capacitor

For this application the output capacitor is used primarily to shunt the output ripple current away from the battery.
The output capacitor should be sized to handle the full output ripple current as defined as:

Ic (RMS)

BAT

RMS

(4)

(5)

(6)

(7)

(8)

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SLUS553D - MAY 2003 - REVISED JULY 2005

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Selecting an Input Capacitor

The input capacitor is used to shunt the converter ripple current on the input lines. The capacitor(s) must have
a ripple current (RMS) rating of:

RMS

[Ichg

(1D)]

)

[Ichg

(1D)

RMS

In addition to shunting the converter input ripple when the PWM is operating, the input capacitor also acts as
part of an LC filter, where the inductance component is defined by the ac adapter cable inductance and board
trace inductance from adapter connector to filter capacitor. Overshoot conditions can be observed at V

line

during fast load transients when the adapter powers the load or when the adapter is hot-plugged .

Increasing the input capacitor value decreases the overshoot at V

. Avoid overshoot voltages at V

in excess

of the absolute maximum ratings for that pin.

Compensating the Loop

For the bq24702/bq24703 used as a buck converter, the best method of compensation is to use a Type II
compensation network from the output of the transconductance amplifiers (COMP pin) to ground (GND) as
shown in Figure 2. A Type II compensation adds a pole-zero pair and an additional pole at dc.

The Type II compensation network places a zero at

1
2

COMP

and a pole at

1
2

COMP

For this battery charger application the following component values: C

= 4.7

F, C

= 150 pF, and

COMP

= 100

, provides a closed loop response with more than sufficient phase margin, as long as the LC

pole [1/2

sqrt (l

c)] is set below 10 kHz. The SRP/SRN filter (R19, R21, C8) and ACP/ACN filter

(R13/R15/C3) are required to filter noise associated with the PWM switching. To avoid adding secondary poles
to the PWM closed loop system those filters should be set with cutoff frequencies higher than 1 kHz.

Selector Operation

The bq24702/bq24703 allows the host controller to manually select the battery as the system's main power
source, without having to remove adapter power. This allows battery conditioning through smart battery learn
cycles. In addition, the bq24702/bq24703 supports autonomous supply selection during fault conditions on
either supply. The selector function uses low R

DS(on)

P-channel MOSFETs for reduced voltage drops and longer

battery run times.

NOTE: Selection of battery power whether manual or automatic results in the suspension of battery
charging.

(9)

(10)

(11)

bq24702, bq24703

SLUS553D - MAY 2003 - REVISED JULY 2005

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UDG-00119

(bq24702)

BATTERY

SELECTOR

CONTROL

BATDRV

ACDRV

BATTERY

SELECT
SWITCH

ADAPTER SELECT SWITCH

ADAPTER

INPUT

SYSTEM

LOAD

PWM

BATTERY

CHARGER

BAT

(bq24702)

Figure 6. Selector Control Switches

Autonomous Selection Operation

Adapter voltage information is sensed at the ACDET pin via a resistor divider from the adapter input. The voltage
on the ACDET pin is compared to an internally fixed threshold. An ACDET voltage less than the set threshold
is considered as a loss of adapter power regardless of the actual voltage at the adapter input. Information
concerning the status of adapter power is fed back to the host controller through ACPRES. The presence of
adapter power is indicated by ACPRES being set high. A loss of adapter power is indicated by ACPRES going
low regardless of which power source is powering the system. During a loss of adapter power, the
bq24702/bq24703 obtains operating power from the battery through the body diode of the P-channel battery
select MOSFET. Under a loss of adapter power, ACPRES (normally high) goes low, if adapter power is selected
to power the system, the bq24702/bq24703 automatically switches over to battery power by commanding
ACDRV high and BATDRV low. During the switch transition period, battery power is supplied to the load via the
body diode of the battery select P-channel MOSFET. When adapter power is restored, the bq24702/bq24703
configures the selector switches according to the state of signals; ACSEL, and ACPRES. If the ACSEL pin is
left high when ac power is restored, the bq24702/bq24703 automatically switches back to ac power. To remain
on battery power after ac power is restored, the ACSEL pin must be brought low.

Conversely, if the battery is removed while the system is running on battery power and adapter power is present,
the bq24702/bq24703 automatically switches over to adapter power by commanding BATDRV high and
ACDRV low.

NOTE: For the bq24702 any fault condition that results in the selector MOSFET switches not
matching their programmed states is indicated by the ALARM pin momentarily going high. Refer
to Battery Depletion Detection Section for more information on the ALARM discrete.

When switching between the ac adapter and battery the internal logic monitors the voltage at pins ACDRV and
BATDRV to implement a break-before-make function, with typical dead time on the order of 150 nsec.

The turnon times for the external ac/battery switches can be increased to minimize inrush peak currents; that
can be accomplished by adding external resistors in series with the MOSFET gates(R18 and R26). Note,
however, that adding those resistors effectively disables the internal break-before-make function for
ac/battery-switches, as the MOSFET gate voltages can not be monitored directly. If external resistors are added
to increase the rise/fall times for battery/ac switches the break-before-make has to be implemented with discrete
external components, to avoid shoot-through currents between ac adapter and battery pack. This functionality
can be implemented by adding diodes (D2/D9) that bypass the external resistors when turning off the external
FETs.

bq24702, bq24703

SLUS553D - MAY 2003 - REVISED JULY 2005

www.ti.com

Smart Learn Cycles When Adapter Power Is Present

Smart learn cycles can be conducted when adapter power is present by asserting and maintaining the ACSEL
pin low. The adapter power can be reselected at the end of the learn cycle by a setting ACSEL to a logic high,
provided that adapter power is present. Battery charging is suspended while selected as the system power
source.

NOTE: On the bq24703 the ac adapter is switched to the load when the battery voltage reaches
the battery depleted threshold; it can be used when the learn cycle does not require the battery
voltage to go below the battery depleted threshold. If the learn cycle algorithm requires the battery
voltage to go lower than the battery depleted voltage, the bq24702 should be used, as it does not
switch the ac adapter to load upon battery depleted detection.

System Break Before Make Function

When selecting the battery as the system primary power source, the adapter power select MOSFET turns off,
in a break-before-make fashion, before the battery select MOSFET turns on. To ensure that this happens under
all load conditions, the system voltage (load voltage) can be monitored through a resistor divider on the VS pin.
This function provides protection against switching over to battery power if the adapter selector switch were
shorted and adapter power present. Setting the VS resistive divider gain with the same gain selected for the
BATP resistive divider assures the battery switch is turned on only when the system voltage is equal or less than
the battery voltage. This function can be eliminated by grounding the VS pin.

The ACDET function senses the adapter voltage via a resistive divider (refer to application circuit).The divider
can be connected either to the anode of the input blocking diode (directly to the adapter supply) or to the cathode
of the input blocking diode (bq24702/3 VCC pin). When the divider is connected to the adapter supply, the
adapter power removal is immediately identified and the sleep mode is entered, disabling the
break-before-make function for system voltage (see section for system power switching) and coupling system
voltage to the battery line. In normal operation with a battery present, the battery low impedance prevents any
over-voltage conditions. However, if a pack is not present or the pack is open, the battery line voltage has a
transient equal to the adapter voltage. The bq24703 SRP/SRN pins are designed to withstand this over-voltage
condition, but avoid connection to the battery line of any external devices that are not rated to withstand the
adapter voltage.

Connecting the ACDET resistive divider input to the VCC node keeps the system break-before-make function
enabled until the voltage at pin VS is lower than the voltage at pin BATP. However, note that when using this
topology the VCC pin voltage can be held by capacitive loads at either the VCC or system (ac switch is on) nodes
when the ac adapter is removed. As the ACDET divider is connected to the VCC line there is a time delay from
ac adapter removal to ac adapter removal detection by the IC. This time is dependent on load conditions and
capacitive load values at VCC and system lines.

Battery Depletion Detection

The bq24702/bq24703 provides the host controller with a battery depletion discrete, the ALARM pin, to alert
the host when a depleted battery condition occurs. The battery depletion level is set by the voltage applied to
the BATDEP pin through a voltage divider network. The ALARM output asserts high and remains high as long
as the battery deplete condition exists, regardless of the power source selected.

For the bq24702, the host controller must take appropriate action during a battery deplete condition to select
the proper power source. The bq24702 remains on the selected power source. The bq24703, however,
automatically reverts over to adapter power, provided the adapter is present, during a deep discharge state. The
battery is considered as being in a deep discharge state when the battery voltage is less than (0.8

depleted

level).

Feature sets for the bq24702 and bq24703 are detailed in Table 1.

bq24702, bq24703

SLUS553D - MAY 2003 - REVISED JULY 2005

www.ti.com

PWM SELECTOR SWITCH GATE DRIVE

Because the external P-channel MOSFETs (as well as the internal MOSFETs) have a maximum gate-source
voltage limitation of the input voltage, VCC, cannot be used directly to drive the MOSFET gate under all input
conditions. To provide safe MOSFET-gate-drive at input voltages of less than an intermediate gate drive voltage
rail was established (VSHP). Where V

HSP

= VCC - 10 V. This ensures adequate enhancement voltage across

all operating conditions.

An external zener diode (D3) connected between VCC and VHSP is required for transient protection; its
breakdown voltage should be above the maximum value for internal VHSP/VCC clamp voltage for all operating
conditions.

TRANSIENT CONDITIONS AT SYSTEM, OVER-VOLTAGE AT SYSTEM TERMINAL

Overshoot conditions can be observed at the system terminal due to fast load transients and inductive
characteristics of the system terminal to load connection. An overshoot at the system terminal can be directly
coupled to the VCC and VBAT nodes, depending on the switch mode of operation. If the capacitors at VBAT
and VCC can not reduce this overshoot to values below the absolute maximum ratings, it is recommended that
an additional capacitor is added to the system terminal to avoid damage to IC or external components due to
voltage overstress under those transient conditions.

AC ADAPTER COLLAPSING DUE TO TRANSIENT CONDITIONS

The ac adapter voltage collapses when the ac switch is on and a current load transient at the system exceeds
the adapter current limit protection. Under those conditions the ac switch is turned off when the ac adapter
voltage falls below the ac adapter detection threshold. If the system terminal to load impedance has an inductive
characteristic, a negative voltage spike can be generated at the system terminal and coupled into the battery
line via the battery switch backgate diode.

In normal operation, with a battery present, this is not an issue, as the low battery impedance holds the voltage
at battery line. However, if a battery is not present or the pack protector switches are open the negative spike
at the system terminal is directly coupled to the SRP/SRN pins via the R19/R21 resistors.

Avoid damage to the SRP/SRN pins if this transient condition happens in the application. If a negative voltage
spike happens at system terminal and R19/R21 limit the current sourced from the pin to less than -50 mA (Ipin
= Vsystem/R19), the pins SRP/SRN are not damaged and the external protection schottky diodes are not
required. However, if the current under those transient conditions exceeds -50 mA, external schottky diodes
must be added to clamp the voltage at pins SRP/SRN so they do not exceed the absolute maximum ratings
specified (-0.3 V).

IBAT AMPLIFIER

A filter with a cutoff frequency smaller than 10 kHz should be added to the IBAT output to remove switching
noise.

POWER DISSIPATION CALCULATION

During PWM operation, the power dissipated internally to the IC increases as the internal driver is switching the
PWM FET on/off. The power dissipation figures are dependent on the external FET used, and can be calculated
using the following equation:

Pd(max) = [IDDOP + Qg

Fs(max)]

VADAP

where:

Qg= Total gate charge for selected PWM MOSFET
IDDOP = Maximum quiescent current for IC
VADAP = Maximum adapter voltage
Fs(max) = Maximum PWM switching frequency

The maximum junction temperature for the IC must be limited to 125

C, under worst case conditions.

bq24702, bq24703

SLUS553D - MAY 2003 - REVISED JULY 2005

www.ti.com

TYPICAL CHARACTERISTICS

Figure 8

1.175

1.18

1.185

1.19

1.195

1.2

1.205

1.21

1.215

-40

110

Error

Amplifier Reference - V

VCC = 18 V

ERROR AMPLIFIER REFERENCE

JUNCTION TEMPERATURE

TJ - Junction Temperature -

125

Figure 9

4.9

4.92

4.94

4.96

4.98

5.02

5.04

5.06

5.08

5.1

-40

110

VREF - 5 -V Reference - V

VCC = 18 V

BYPASSED 5-V REFERENCE

JUNCTION TEMPERATURE

TJ - Junction Temperature -

125

Figure 10

TOTAL SLEEP CURRENT

JUNCTION TEMPERATURE

TJ - Junction Temperature -

-40

110

I SLEEP

- Battery Sleep Current -

VCC = 18 V

125

Figure 11

OSCILLATOR FREQUENCY

JUNCTION TEMPERATURE

TJ - Junction Temperature -

235

245

255

265

275

285

295

305

315

325

335

-40

110

f - Oscillator Frequency - kHz

VCC = 18 V

125

bq24702, bq24703

SLUS553D - MAY 2003 - REVISED JULY 2005

www.ti.com

Figure 12

BATTERY CURRENT SET ACCURACY

BATTERY CURRENT SET VOLTAGE

VSRSET - Battery Current Set Voltage - V

0.25

0.75

1.25

1.75

2.25

SRSET Full Scale = 2.5 V

= Max Programmed Current

TJ = 25

Battery Current Set

Accuracy - %

0.5

1.5

2.5

Figure 13

AC CURRENT SET ACCURACY

AC CURRENT SET VOLTAGE

VACSET - AC Current Set Voltage - V

0.25

0.75

1.25

1.75

2.25

AC Current Set

Accuracy - %

ACSET Full Scale = 2.5 V

= Max Programmed Current

TJ = 25

0.5

1.5

2.5

BOARD LAYOUT GUIDELINES

Recommended Board Layout

Follow these guidelines when implementing the board layout:

Do not place lines and components dedicated to battery/adapter voltage sensing (ACDET,BATDEP, VS),
voltage feedback loop (BATP, BATSET if external reference is used) and shunt voltage sensing
(SRP/SRN/ACP/ACN) close to lines that have signals with high dv/dt (PWM, BATDRV, ACDRV, VHSP) to
avoid noise coupling.

Add filter capacitors for SRP/SRN (C8) and ACP/ACN (C3) close to IC pins

Add Reference filter capacitor C1 close to IC pins

Use an isolated, clean ground for IC ground pin and resistive dividers used in voltage sensing; use an
isolated power ground for PWM filter cap and diode (C11/D4). Connect the grounds to the battery PACK-
and adapter GND.

Place C7 close to VCC pin.

Place input capacitor C12 close to PWM switch (U3) source and R14.

Position ac switch (U2) to minimize trace length from ac switch source to input capacitor C12.

Minimize inductance of trace connecting PWM pin and PWM external switch U3 gate

Maximize power dissipation planes connected to PWM switch

10. Maximize power dissipation planes connected to SRP resistor if steady state in zero volt mode is possible

11. Maximize power dissipation planes connected to D1

PACKAGING INFORMATION

Orderable Device

Status

(1)

Package

Type

Package

Drawing

Pins Package

Qty

Eco Plan

(2)

Lead/Ball Finish

MSL Peak Temp

(3)

BQ24702PW

ACTIVE

TSSOP

Green (RoHS &

no Sb/Br)

CU NIPDAU

Level-1-260C-UNLIM

BQ24702PWG4

ACTIVE

TSSOP

Green (RoHS &

no Sb/Br)

CU NIPDAU

Level-1-260C-UNLIM

BQ24702PWR

ACTIVE

TSSOP

2000 Green (RoHS &

no Sb/Br)

CU NIPDAU

Level-1-260C-UNLIM

BQ24702PWRG4

ACTIVE

TSSOP

2000 Green (RoHS &

no Sb/Br)

CU NIPDAU

Level-1-260C-UNLIM

BQ24703PW

ACTIVE

TSSOP

Green (RoHS &

no Sb/Br)

CU NIPDAU

Level-1-260C-UNLIM

BQ24703PWR

ACTIVE

TSSOP

2000 Green (RoHS &

no Sb/Br)

CU NIPDAU

Level-1-260C-UNLIM

BQ24703PWRG4

ACTIVE

TSSOP

2000 Green (RoHS &

no Sb/Br)

CU NIPDAU

Level-1-260C-UNLIM

BQ24703RHDR

ACTIVE

QFN

RHD

3000 Green (RoHS &

no Sb/Br)

CU NIPDAU

Level-2-260C-1 YEAR

BQ24703RHDRG4

ACTIVE

QFN

RHD

3000 Green (RoHS &

no Sb/Br)

CU NIPDAU

Level-2-260C-1 YEAR

(1)

The marketing status values are defined as follows:

ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in
a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.

(2)

Eco

Plan

The

planned

eco-friendly

classification:

Pb-Free

(RoHS)

Green

(RoHS

Sb/Br)

please

check

http://www.ti.com/productcontent

for the latest availability information and additional product content details.

TBD: The Pb-Free/Green conversion plan has not been defined.
Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements
for all 6 substances, including the requirement that lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered
at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes.
Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame
retardants (Br or Sb do not exceed 0.1% by weight in homogeneous material)

(3)

MSL, Peak Temp. -- The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder

temperature.

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In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI
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PACKAGE OPTION ADDENDUM

www.ti.com

27-Sep-2005

Addendum-Page 1

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