Features

Fast charge and conditioning of

nickel cadmium or nickel-metal
hydride batteries

Hysteretic PWM switch-mode

current regulation or gated con-
trol of an external regulator

Easily integrated into systems or

used as a stand-alone charger

Pre-charge qualification of tem-

perature and voltage

Configurable, direct LED outputs

display battery and charge status

Fast-charge termination by tem-

perature/

time, peak volume de-

tection, -

V, maximum voltage,

maximum temperature, and maxi-
mum time

Optional top-off charge and

pu ls e d cu rre nt mai nten anc e
charging

Logic-level controlled low-power

mode (< 5

µA standby current)

General Description

The bq2004 Fast Charge IC provides
comprehensive fast charge control
functions together with high-speed
switching power control circuitry on a
monolithic CMOS device.

Integration of closed-loop current
control circuitry allows the bq2004
to be the basis of a cost-effective so-
lution for stand-alone and system-
integrated chargers for batteries of
one or more cells.

Switch-activated discharge-before-
charge allows bq2004-based chargers
to support battery conditioning and
capacity determination.

High-efficiency power conversion is
accomplished using the bq2004 as a
hysteretic PWM controller for
switch-mode regulation of the charg-
ing current. The bq2004 may alterna-
tively be used to gate an externally
regulated charging current.

Fast charge may begin on application
of the charging supply, replacement

of the battery, or switch depression.
For safety, fast charge is inhibited
unless/until the battery tempera-
ture and voltage are within config-
ured limits.

Temperature, voltage, and time are
monitored throughout fast charge.
Fast charge is terminated by any of
the following:

Rate of temperature time
(

T/t)

Peak voltage detection (PVD)

Negative delta voltage (-

Maximum voltage

Maximum temperature

Maximum time

After fast charge, optional top-off
and pulsed current maintenance
phases are available.

Fast-Charge IC

bq2004

DCMD

Discharge command

DSEL

Display select

VSEL

Voltage termination
select

Timer mode select 1

Timer mode select 2

TCO

Temperature cutoff

Temperature sense

BAT

Battery voltage

PN2004E01.eps

16-Pin Narrow DIP

or Narrow SOIC

INH

DIS

MOD

VCC

VSS

LED2

LED1

SNS

DCMD

DSEL

VSEL

TM1

TM2

TCO

BAT

SNS

Sense resistor input

LED

Charge status output 1

LED

Charge status output 2

System ground

5.0V

±10% power

MOD

Charge current control

DIS

Discharge control
output

INH

Charge inhibit input

Pin Connections

SLUS063JUNE 1999 F

Pin Names

Pin Descriptions

DCMD

Discharge-before-charge control input

The DCMD input controls the conditions
that enable discharge-before-charge. DCMD
is pulled up internally.

A negative-going

pulse on DCMD initiates a discharge to end-
of-discharge voltage (EDV) on the BAT pin,
followed by a new charge cycle start. Tying
D C M D t o g r o u n d e n a b l e s a u t o m a t i c
discharge-before-charge on every new charge
cycle start.

DSEL

Display select input

This three-state input configures the charge
status display mode of the LED

and LED

outputs. See Table 2.

VSEL

Voltage termination select input

This three-state input controls the voltage-
termination technique used by the bq2004.
When high, PVD is active.

When floating,

V is used. When pulled low, both PVD and

V are disabled.

Timer mode inputs

and TM

are three-state inputs that

configure the fast charge safety timer, voltage
termination hold-off time, "top-off ", and
trickle charge control. See Table 1.

TCO

Temperature cut-off threshold input

Input to set maximum allowable battery
temperature.

If the potential between TS

and SNS is less than the voltage at the TCO
input, then fast charge or top-off charge is ter-
minated.

Temperature sense input

Input, referenced to SNS,

for an external

thermister monitoring battery temperature.

BAT

Battery voltage input

BAT is the battery voltage sense input, refer-
enced to SNS.

This is created by a high-

impedance resistor-divider network con-
nected between the positive and the negative
terminals of the battery.

SNS

Charging current sense input

SNS controls the switching of MOD based on
an external sense resistor in the current
path of the battery. SNS is the reference po-
tential for both the TS and BAT pins.

SNS is connected to V

, then MOD switches

high at the beginning of charge and low at
the end of charge.

LED

Charge status outputs

Push-pull outputs indicating charging
status. See Table 2.

Ground

supply input

5.0V,

±10% power input.

MOD

Charge current control output

MOD is a push-pull output that is used to
control the charging current to the battery.
MOD switches high to enable charging cur-
rent to flow and low to inhibit charging
current flow.

DIS

Discharge control output

Push-pull output used to control an external
transistor to discharge the battery before
charging.

INH

Charge inhibit input

When low, the bq2004 suspends all charge
actions, drives all outputs to high imped-
ance, and assumes a low-power operational
state. When transitioning from low to high, a
new charge cycle is started.

bq2004

Functional Description

Figure 3 shows a block diagram and Figure 4 shows a
state diagram of the bq2004.

Battery Voltage and Temperature
Measurements

Battery voltage and temperature are monitored for
maximum allowable values. The voltage presented on
the battery sense input, BAT, should represent a
two-cell potential for the battery under charge.

resistor-divider ratio of:

RB1

RB2

- 1

is recommended to maintain the battery voltage within
the valid range, where N is the number of cells, RB1 is
the resistor connected to the positive battery terminal,
and RB2 is the resistor connected to the negative bat-
tery terminal. See Figure 1.

Note: This resistor-divider network input impedance to
end-to-end should be at least 200k

and less than 1M.

A ground-referenced negative temperature coefficient ther-
mistor placed in proximity to the battery may be used as a
low-cost temperature-to-voltage transducer. The tempera-
ture sense voltage input at TS is developed using a
resistor-thermistor network between V

and V

See

Figure 1. Both the BAT and TS inputs are referenced to
SNS, so the signals used inside the IC are:

BAT

- V

SNS

= V

CELL

and

- V

SNS

= V

TEMP

Discharge-Before-Charge

The DCMD input is used to command discharge-before-
charge via the DIS output. Once activated, DIS becomes
active (high) until V

CELL

falls below V

EDV,

at which time

DIS goes low and a new fast charge cycle begins.

The DCMD input is internally pulled up to V

(its inac-

tive state). Leaving the input unconnected, therefore,
results in disabling discharge-before-charge. A negative
going pulse on DCMD initiates discharge-before-charge
at any time regardless of the current state of the
bq2004. If DCMD is tied to V

, discharge-before-charge

will be the first step in all newly started charge cycles.

Starting a Charge Cycle

A new charge cycle (see Figure 2) is started by:

rising above 4.5V

CELL

falling through the maximum cell voltage,

MCV

where:

MCV

= 0.8

± 30mV

A transition on the INH input from low to high.

If DCMD is tied low, a discharge-before-charge is exe-
cuted as the first step of the new charge cycle. Other-
wise, pre-charge qualification testing is the first step.

The battery must be within the configured temperature
and voltage limits before fast charging begins.

The valid battery voltage range is V

EDV

< V

BAT

< V

MCV

where:

EDV

= 0.4

± 30mV

The valid temperature range is V

HTF

< V

TEMP

< V

LTF

where:

bq2004

Fg2004a.eps

N
T
C

bq2004

VCC

PACK +

PACK -

SNS

RT1

RT2

RB2

RB1

bq2004

Negative Temperature

Coefficient Thermister

PACK+

PACK-

BAT

SNS

Figure 1. Voltage and Temperature Monitoring

LTF

= 0.4

± 30mV

HTF

= [(1/4

LTF

) + (3/4

TCO

)]

± 30mV

Note: The low temperature fault (LTF) threshold is not
enforced if

the IC is configured for PVD termination

(VSEL = high).

TCO

is the voltage presented at the TCO input pin, and is

configured by the user with a resistor divider between V

and ground. The allowed range is 0.2 to 0.4

If the temperature of the battery is out of range, or the
voltage is too low, the chip enters the charge pending
state and waits for both conditions to fall within their al-
lowed limits. The MOD output is modulated to provide
the configured trickle charge rate in the charge pending
state.

There is no time limit on the charge pending

state; the charger remains in this state as long as the
voltage or temperature conditons are outside of the al-
lowed limits. If the voltage is too high, the chip goes to
the battery absent state and waits until a new charge
cycle is started.

Fast charge continues until termination by one or more
of the six possible termination conditions:

Delta temperature/delta time (

T/t)

Peak voltage detection (PVD)

Negative delta voltage (-

Maximum voltage

Maximum temperature

Maximum time

PVD and -

V Termination

The bq2004 samples the voltage at the BAT pin once
every 34s. When -

V termination is selected, if V

CELL

lower than any previously measured value by 12mV
±4mV (6mV/cell), fast charge is terminated. When PVD
termination is selected, if V

CELL

is lower than any previ-

ously measured value by 6mV

±2mV (3mV/cell), fast

charge is terminated. The PVD and -

V tests are valid

in the range 0.4

< V

CELL

< 0.8

Voltage Sampling

Each sample is an average of voltage measurements
taken 57

µs apart. The IC takes 32 measurements in

PVD mode and 16 measurements in -

V mode. The re-

sulting sample periods (9.17ms and 18.18ms, respec-
tively) filter out harmonics centered around 55Hz and
109Hz. This technique minimizes the effect of any AC
line ripple that may feed through the power supply from
either 50Hz or 60Hz AC sources. Tolerance on all tim-
ing is

±16%.

Voltage Termination Hold-off

A hold-off period occurs at the start of fast charging.
During the hold-off period, -

V termination is disabled.

This avoids premature termination on the voltage
spikes sometimes produced by older batteries when
fast-charge current is first applied.

T/t, maximum

voltage and maximum temperature terminations are
not affected by the hold-off period.

T/t Termination

The bq2004 samples at the voltage at the TS pin every
34s, and compares it to the value measured two samples
earlier. If V

TEMP

has fallen 16mV

±4mV or more, fast

charge is terminated. If VSEL = high, the

T/t termi-

nation test is valid only when V

TCO

< V

TEMP

< V

TCO

0.2

. Otherwise the

T/t termination test is valid

only when V

TCO

< V

TEMP

< V

LTF

Temperature Sampling

Each sample is an average of 16 voltage measurements
taken 57

µs apart. The resulting sample period

(18.18ms) filters out harmonics around 55Hz. This tech-
nique minimizes the effect of any AC line ripple that
may feed through the power supply from either 50Hz or
60Hz AC sources. Tolerance on all timing is

±16%.

Maximum Voltage, Temperature, and Time

Anytime V

CELL

rises above V

MCV,

the LEDs go off and

charging ceases immediately. If V

CELL

then falls back be-

low V

MCV

before t

MCV

= 1.5s

±0.5s, the chip transitions to

the Charge Complete state (maximum voltage termina-
tion). If V

CELL

remains above V

MCV

at the expiration of

MCV,

the bq2004 transitions to the Battery Absent state

(battery removal). See Figure 4.

Maximum temperature termination occurs anytime
V

TEMP

falls below the temperature cutoff threshold

TCO

Unless PVD termination is enabled (VSEL =

high), charge will also be terminated if V

TEMP

rises

above the low temperature fault threshold, V

LTF

, after

fast charge begins. The V

LTF

threshold is not enforced

when the IC is configured for PVD termination.

Maximum charge time is configured using the TM pin.
Time settings are available for corresponding charge
rates of C/4, C/2, 1C, and 2C. Maximum time-out termi-
nation is enforced on the fast-charge phase, then reset,
and enforced again on the top-off phase, if selected.
There is no time limit on the trickle-charge phase.

bq2004

VSEL Input

Voltage Termination

Low

Disabled

Float

High

PVD

Top-off Charge

An optional top-off charge phase may be selected to
follow fast charge termination for the C/2 through 4C
rates. This phase may be necessary on NiMH or other
battery chemistries that have a tendency to terminate
charge prior to reaching full capacity. With top-off en-
abled, charging continues at a reduced rate after
fast-charge termination for a period of time equal to
the fast-charge safety time (See Table 1.) During top-
off, the MOD pin is enabled at a duty cycle of 260

µs ac-

tive for every 1820

µs inactive. This modulation results

in an average rate 1/8th that of the fast charge rate.
Maximum voltage, time, and temperature are the only
termination methods enabled during top-off.

Pulse-Trickle Charge

Pulse-trickle charging follows the fast charge and op-
tional top-off charge phases to compensate for self-
discharge of the battery while it is idle in the charger.
The configured pulse-trickle rate is also applied in the
charge pending state to raise the voltage of an over-
discharged battery up to the minimum required before
fast charge can begin.

In the pulse-trickle mode, MOD is active for 260

µs of a

period specified by the settings of TM1 and TM2. See
Table 1. The resulting trickle-charge rate is C/64 when
top-off is enabled and C/32 when top-off is disabled.
Both pulse trickle and top-off may be disabled by tying
TM1 and TM2 to V

Charge Status Indication

Charge status is indicated by the LED

and LED

out-

puts. The state of these outputs in the various charge cy-
cle phases is given in Table 2 and illustrated in Figure 2.

In all cases, if V

CELL

exceeds the voltage at the MCV

pin, both LED

and LED

outputs are held low regard-

less of other conditions. Both can be used to directly
drive an LED.

Charge Current Control

The bq2004 controls charge current through the MOD
output pin. The current control circuitry is designed to
support implementation of a constant-current switching
regulator or to gate an externally regulated current
source.

When used in switch mode configuration, the nominal
regulated current is:

REG

= 0.225V/R

SNS

Charge current is monitored at the SNS input by the
voltage drop across a sense resistor, R

SNS

, between the

low side of the battery pack and ground. R

SNS

is sized to

provide the desired fast charge current.

If the voltage at the SNS pin is less than V

SNSLO

, the

MOD output is switched high to pass charge current to
the battery.

Corresponding

Fast-Charge

Rate

TM1

TM2

Typical

Fast-Charge Safety

Time (minutes)

Typical

PVD, -

V Hold-Off

Time (seconds)

Top-Off

Rate

Pulse-

Trickle

Rate

Pulse-

Trickle

Period (Hz)

C/4

Low

360

137

Disabled

C/2

Float

Low

180

820

Disabled

C/32

240

High

Low

410

Disabled

C/32

120

Low

Float

200

Disabled

C/32

Float

100

Disabled

C/32

C/2

High

Float

180

820

C/16

C/64

120

Low

High

410

C/8

C/64

Float

High

200

C/4

C/64

High

100

C/2

C/64

Note:

Typical conditions = 25°C, V

= 5.0V.

Table 1. Fast-Charge Safety Time/Hold-Off/Top-Off Table

bq2004

When the SNS voltage is greater than V

SNSHI

, the MOD

output is switched low--shutting off charging current to
the battery.

SNSLO

= 0.04

± 25mV

SNSHI

= 0.05

± 25mV

When used to gate an externally regulated current
source, the SNS pin is connected to V

, and no sense re-

sisitor is required.

BD200401.eps

Timing

Control

OSC

Display
Control

Charge Control

State Machine

Discharge

Control

MOD

Control

TCO

Check

LTF

Check

A/D

EDV

Check

MCV

Check

DIS

MOD

INH

VCC VSS

BAT

SNS

TCO

TM2

TM1

LED1

DCMD

DVEN

VTS - VSNS

VBAT - VSNS

LED2

DSEL

PWR

Control

Figure 3. Block Diagram

Mode 1

Charge Status

LED

DSEL = V

Battery absent

Low

Fast charge pending or discharge-before-charge in progress

High

Fast charge in progress

Low

High

Charge complete, top-off, and/or trickle

High

Low

Mode 2

Charge Status

LED

DSEL = Floating

Battery absent, fast charge in progress or complete

Low

Fast charge pending

High

Low

Discharge in progress

Low

High

Top-off in progress

High

Mode 3

Charge Status

LED

DSEL = V

Battery absent

Low

Fast charge pending or discharge-before-charge in progress

Low

1/8s high

1/8s low

Fast charge in progress

Low

High

Fast charge complete, top-off, and/or trickle

High

Low

Table 2. bq2004 LED Status Display Options

bq2004

Charge
Pending

DCMD Tied to Ground?

Rising Edge

on DCMD

Discharge-

Before-Charge

Pulse

Trickle

Charge

Pulse

Trickle

Charge

Pulse

Trickle

Charge

Pulse

Trickle

Charge

Top-Off

Charge

Fast

Charge

Battery Voltage?

Battery Temperature?

Top-Off

Selected?

New Charge Cycle Started by

Any One of:

VCC Rising to Valid Level

Battery Replacement

(VCELL Falling through VMCV)

Inhibit (INH) Released

VEDV < VCELL < VMCV
and

VHTF < VTEMP < VLTF*

VEDV < VCELL < VMCV

VTEMP > VLTF or

VTEMP < VHTF

VCELL < VEDV

Yes

*VSEL = High disables LTF threshold enforcement

t > t

MCV

> VMCV

VCELL

> VMCV

VCELL

VMCV

VCELL
VMCV

VCELL

VMCV

Charge
Complete

Battery
Absent

or Maximum
Time Out

VTEMP < VTCO

SD2004.eps

VCELL

VMCV

- V or

T/ t or

VTEMP

VTCO

or
Maximum Time Out

Figure 4. State Diagram

bq2004

Absolute Maximum Ratings

Symbol

Parameter

Minimum

Maximum

Unit

Notes

relative to V

-0.3

+7.0

DC voltage applied on any pin ex-
cluding V

relative to V

-0.3

+7.0

OPR

Operating ambient temperature

-20

+70

°C

Commercial

STG

Storage temperature

-55

+125

°C

SOLDER

Soldering temperature

+260

°C

10 sec max.

BIAS

Temperature under bias

-40

+85

°C

Note:

Permanent device damage may occur if Absolute Maximum Ratings are exceeded. Functional opera-
tion should be limited to the Recommended DC Operating Conditions detailed in this data sheet. Expo-
sure to conditions beyond the operational limits for extended periods of time may affect device reliability.

DC Thresholds

(TA = TOPR; VCC

±10%)

Symbol

Parameter

Rating

Tolerance

Unit

Notes

SNSHI

High threshold at SNS result-
ing in MOD = Low

0.05 * V

±0.025

SNSLO

Low threshold at SNS result-
ing in MOD = High

0.04 * V

±0.010

LTF

Low-temperature fault

0.4 * V

±0.030

TEMP

LTF

inhib-

its/terminates charge

HTF

High-temperature fault

(1/4 * V

LTF

) + (2/3 * V

TCO

)

±0.030

TEMP

HTF

inhibits

charge

EDV

End-of-discharge voltage

0.4 * V

±0.030

CELL

< V

EDV

inhibits

fast charge

MCV

Maximum cell voltage

0.8 * V

±0.030

CELL

> V

MCV

inhibits/

terminates charge

THERM

TS input change for

T/t

detection

-16

±4

= 5V, T

= 25

°C

BAT input change for -

detection

-12

±4

= 5V, T

= 25

°C

PVD

BAT input change for PVD
detection

-6

±2

= 5V, T

= 25

°C

bq2004

Recommended DC Operating Conditions

(TA = TOPR)

Symbol

Condition

Minimum

Typical

Maximum

Unit

Notes

Supply voltage

4.5

5.0

5.5

BAT

Battery input

CELL

BAT voltage potential

BAT

- V

SNS

Thermistor input

TEMP

TS voltage potential

- V

SNS

TCO

Temperature cutoff

0.2 * V

0.4 * V

Valid

T/t range

Logic input high

2.0

DCMD, INH

Logic input high

- 0.3

, TM

, DSEL, VSEL

Logic input low

0.8

DCMD, INH

Logic input low

0.3

, TM

, DSEL, VSEL

Logic output high

- 0.8

DIS, MOD, LED

, LED

-10mA

Logic output low

0.8

DIS, MOD, LED

, LED

10mA

Supply current

Outputs unloaded

Standby current

µA

INH = V

DIS, LED

, LED

, MOD source

-10

= V

- 0.8V

DIS, LED

, LED

, MOD sink

= V

+ 0.8V

Input leakage

±1

µA

INH, BAT, V = V

to V

Input leakage

400

µA

DCMD, V = V

to V

Logic input low source

µA

, TM

, DSEL, VSEL,

V = V

to V

+ 0.3V

Logic input high source

-70

µA

, TM

, DSEL, VSEL,

V = V

- 0.3V to V

Tri-state

-2

µA

, TM

, DSEL, and VSEL

should be left disconnected
(floating) for Z logic input state

Note:

All voltages relative to V

except as noted.

bq2004

bq2004

Data Sheet Revision History

Change No.

Page No.

Description

Nature of Change

Standby current ISB

Was 5

µA max; is 1 µA max

BSNSLO

Rating

Was: V

SNSHI

- (0.01 * V

)

Is: 0.04 * V

Correction in Peak Voltage Detect Termination section Was VCELL; is VBAT

Added block diagram

Diagram insertion

Added VSEL/termination table

Table insertion

Added values to Table 3

Top-off rate values

VSEL/Termination

Low, High changed

All

Revised and expanded format of this data sheet

Clarification

Corrected V

HTF

rating

Was: (1/3

LTF

) + (2/3

TCO

)

Is: (1/4

LTF

) + (3/4

TCO

)

OPR

Deleted industrial tempera-
ture range

Notes:

Change 1 = Apr. 1994 B "Final" changes from Dec. 1993 A "Preliminary."
Change 2 = Sept. 1996 C changes from Apr. 1994 B.
Change 3 = April 1997 C changes from Sept. 1996 C.
Change 4 = Oct. 1997 D changes from April 1997 C.
Change 5 = Jan. 1998 E changes from Oct. 1997 D.
Change 6 = June 1999 F changes from Jan. 1998 E.

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