Features

Fast charge of nickel cadmium
or nickel-metal hydride batter-
ies

Direct LED output displays
charge status

Fast-charge termination by
rate of rise of temperature,
maximum voltage, maximum
temperature, and maximum
time

Internal band-gap voltage ref-
erence

Optional top-off charge (bq2002T
only)

Selectable pulse-trickle charge
rates (bq2002T only)

Low-power mode

8-pin 300-mil DIP or 150-mil
SOIC

General Description

The bq2002D/T Fast-Charge IC are
low-cost CMOS battery-charge control-
lers able to provide reliable charge ter-
mination for both NiCd and NiMH bat-
tery applications.

Controlling a

current-limited or constant-current
supply allows the bq2002D/T to be the
basis for a cost-effective stand-alone or
system-integrated charger.

The

bq2002D/T integrates fast charge with
optional top-off and pulsed-trickle con-
trol in a single IC for charging one or
more NiCd or NiMH battery cells.

Fast charge is initiated on application
of the charging supply or battery re-
placement. For safety, fast charge is
inhibited if the battery temperature
and voltage are outside configured
limits.

Fast charge is terminated by any of
the following:

Rate of temperature rise

Maximum voltage

Maximum temperature

Maximum time

After fast charge, the bq2002T option-
ally tops-off and pulse-trickles the
battery per the pre-configured limits.
Fast charge may be inhibited using
the INH pin. The bq2002D/T may be
placed in low-standby-power mode to
reduce system power consumption.

NiCd/NiMH Fast-Charge Management ICs

bq2002D/T

Timer mode select input

LED

Charging status output

BAT

Battery voltage input

System ground

PN-200201.eps

8-Pin DIP or

Narrow SOIC

LED

BAT

VSS

INH

VCC

Temperature sense input

Supply voltage input

INH

Charge inhibit input

Charge control output

Pin Connections

Pin Names

bq2002D/T Selection Guide

Part No.

TCO

HTF

LTF

Fast Charge

Time-Out

Top-Off

Maintenance

bq2002D

0.225

0.25

0.4

C/4

320 min

C/64

C/256

80 min

C/16

C/256

40 min

None

C/128

bq2002T

0.225

0.25

None

C/4

440 min

None

110 min

None

55 min

None

SLUS133璊ANUARY 2000 E

Pin Descriptions

Timer mode input

A three-level input that controls the settings
for the fast charge safety timer, voltage ter-
mination mode, top-off, pulse-trickle, and
voltage hold-off time.

LED

Charging output status

Open-drain output that indicates the charging
status.

BAT

Battery input voltage

The battery voltage sense input. The input to
this pin is created by a high-impedance re-
sistor divider network connected between
the positive and negative terminals of the
battery.

System ground

Temperature sense input

Input for an external battery temperature
monitoring thermistor.

Supply voltage input

5.0V

�20% power input.

INH

Charge inhibit input

When high, INH suspends the fast charge in
progress.

When returned low, the IC re-

sumes operation at the point where initially
suspended.

Charge control output

An open-drain output used to control the
charging current to the battery. CC switch-
ing to high impedance (Z) enables charging
current to flow, and low to inhibit charging
current. CC is modulated to provide top-off,
if enabled, and pulse trickle.

Functional Description

Figures 2 and 3 show state diagrams of bq2002D/T and
Figure 4 shows the block diagram of the bq2002D/T

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
single-cell potential for the battery under charge.

resistor-divider ratio of:

RB1

RB2

= N - 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.

bq2002D/T

F2002DT1.eps

bq2002D/T

BAT

VSS

N
T
C

bq2002D/T

VCC

PACK +

VSS

BAT pin connection

Thermistor connection

NTC = negative temperature coefficient thermistor.

RT1

RT2

RB1

RB2

Mid-level

setting for TM

Figure 1. Voltage and Temperature Monitoring and TM Pin Configuration

bq2002D/T

Chip on

VCC 4.0V

Battery Voltage

too High?

Battery

Temperature?

Charge
Pending

Fast Charge,

CC = Z

LED = Low

SD2002D.eps

VBAT < 2V

VBAT < 2V and

VBAT

Off,

CC = Low

LED = Low

Off,

CC = Low

LED = Z

VBAT > 2V

VBAT 2V

VTS > 0.25V VCC

VTS < 0.25V VCC

VBAT > 2V or

VTS < 0.25V VCC or
Maximum Time Out

T/ t or

Figure 2. bq2002D State Diagram

Chip on

VCC 4.0V

Battery Voltage

too High?

( T/ t or
Maximum Time Out)
and TM = High

Battery

Temperature?

Charge
Pending

Fast

LED =

Low

Top-off

LED = Z

SD2002T.eps

VBAT < 2V

VBAT

0.25 VCC < VTS < 0.6 VCC

Trickle

LED =

Low

Trickle

LED = Z

VBAT > 2V or
VTS < 0.225 VCC or
Maximum Time Out

VBAT > 2V or
VTS < 0.225 VCC or
(( T/ t or
Maximum Time Out)
and TM = High)

VBAT < 2V and
VTS < 0.6 VCC and
VTS > 0.25 VCC

VBAT > 2V

VBAT 2V

VTS > 0.6 VCC or
VTS < 0.25 VCC

Figure 3. bq2002T State Diagram

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

and less than 1 M.

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.

Starting A Charge Cycle

Either of two events starts a charge cycle (see Figure 5):

1. Application of power to V

2. Voltage at the BAT pin falling through the maximum
cell voltage where:

MCV

= 2V

�5%.

If the battery is within the configured temperature and
voltage limits, the IC begins fast charge. The valid bat-
tery voltage range is V

BAT

< V

MCV

. The valid tempera-

ture range is V

HTF

< V

LTF

for the bq2002T and

HTF

< V

for the bq2002D where:

LTF

= 0.4

�5%.

HTF

= 0.25

�5% (bq2002T only).

If the battery voltage or temperature is outside of these
limits, the IC pulse-trickle charges until the tempera-
ture falls within the allowed fast charge range or a new
charge cycle is started.

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

Rate of temperature rise

Maximum voltage

Maximum temperature

Maximum time

T/t Termination

The bq2002D/T samples at the voltage at the TS pin ev-
ery 19s and compares it to the value measured three
samples earlier.

If the voltage has fallen 25.6mV or

more, fast charge is terminated. The

T/t termination

test is valid only when V

TCO

< V

LTF

for the

bq2002T and V

TCO

< V

for the bq2002D.

Temperature Sampling

A sample is taken by averaging together 16 measure-
ments taken 57

祍 apart. The resulting sample period

(18.18ms) filters out harmonics around 55Hz. This tech-

bq2002D/T

OSC

LED

VCC

VSS

BAT

INH

Clock

Phase

Generator

Timing

Control

Sample

History

A to D

Converter

MCV

Check

Power

Down

Bd2002TD.eps

Voltage

Reference

Power-On

Reset

TCO

Check

HTF/

LTF

Check

Charge-Control

State Machine

T/ t

ALU

Figure 4. Block Diagram

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

�20%.

Maximum Voltage, Temperature, and Time

Any time the voltage on the BAT pin exceeds the maxi-
mum cell voltage, V

MCV

, fast charge or optional top-off

charge is terminated.

Maximum temperature termination occurs anytime the
voltage on the TS pin falls below the temperature cut-off
threshold V

TCO

where:

TCO

= 0.225

�5%

Maximum charge time is configured using the TM pin.
Time settings are available for corresponding charge
rates of C/4, 1C, and 2C. Maximum time-out termina-
tion is enforced on the fast-charge phase, then reset, and

bq2002D/T

Corresponding

Fast-Charge Rate

Typical Fast-Charge

and Top-Off

Time Limits

(minutes)

Top-Off

Rate

Pulse-

Trickle Rate

Pulse-

Trickle

Period (ms)

bq2002D

C/4

Mid

440

Low

110

High

bq2002T

C/4

Mid

320

C/64

C/256

18.3

Low

C/16

C/256

73.1

High

Disabled

C/128

73.1

Notes:

Typical conditions = 25癈, V

= 5.0V.

Mid = 0.5 * V

�0.5V

Tolerance on all timing is

�20%

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

TD2002F1.eps

Fast Charging

VCC = 0

Fast Charging

CC Output

LED

Charge initiated by application of power

Charge initiated by battery replacement

Pulse-Trickle

Top-Off

(optional,

bq2002T only)

(optional,

bq2002T only)

286

See

Table 1

286

4576

Figure 5. Charge Cycle Phases

协谢械泻褌褉芯薪薪褘泄 泻芯屑锌芯薪械薪褌: BQ2002T

协谢械泻褌褉芯薪薪褘泄泻芯屑锌芯薪械薪褌: BQ2002T