TEXAS INSTRUMENTS bq2002D, bq2002T Technical data

bq2002D/T

NiCd/NiMH Fast-Charge Management ICs

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

Pin Connections

TM

LED

BAT
V

1

2

3

4

SS

8

CC

7

INH

V

6

CC

TS

5

General Description

The bq2002D/T Fast-Charge IC are
low-cost CMOS battery-chargecontrol

­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.

Pin Names

TM Timer mode select input
LED
BAT Battery voltage input
V

SS

Charging status output

System ground

Fast charge is terminated by any of
the following:

Rate of temperature rise

n

-

-

Maximum voltage

n

­Maximum temperature

n

Maximum time

n

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.

-

TS Temperature sense input
V

CC

Supply voltage input
INH Charge inhibit input
CC Charge control output

-

8-Pin DIP or

Narrow SOIC

PN-200201.eps

bq2002D/T Selection Guide

Part No. TCO HTF LTF Fast Charge Time-Out Top-Off Maintenance

C/4 440 min None None

bq2002D

bq2002T

SLUS133B–JULY 2000

0.225 ∗ V

0.225 ∗ V

CC

CC

0.25 ∗ V

0.25 ∗ V

CC

CC

None

0.4 ∗ V

CC

1C 110 min None None
2C 55 min None None

C/4 320 min C/64 C/256

1C 80 min C/16 C/256
2C 40 min None C/128

1

bq2002D/T

Pin Descriptions

TM

LED

BAT

V

SS

TS

V

CC

INH

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.

Charging output status

Open-drain output that indicates the charging
status.

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
T emperaturesenseinput

Input for an external battery temperature
monitoring thermistor.

Supply voltage input

5.0V±20% power input.

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.

CC

-

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 Voltageand 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. A
resistor-dividerratioof

RB1

=N-1

RB2

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 bat­tery terminal. See Figure 1.

-

-

V

CC

RT1

RB1

BAT

bq2002D/T

V

SS

RB2

BAT pin connection Thermistor connection

R3

R4

Mid-level

V

CC

TM

T

bq2002D/T

V

SS

S

RT2

PACK +

N
T
C

setting for TM

NTC = negative temperature coefficient thermistor.

F2002DT1.eps

Figure 1. Voltage and Temperature Monitoring and TM Pin Configuration

2

bq2002D/T

Chip on

4.0V

V

CC

Fast Charge,

CC = Z

LED = Low

V

Top-off

LED = Z

V

CC

Chip on

CC

> 0.25V

V

TS

0.25 VCC < VTS < 0.6 V

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

V

> 2V or

BAT

VTS < 0.225 VCC or
Maximum Time Out

Battery Voltage

V

BAT

too High?

< 2V

V

BAT

>

2V

Battery

Temperature?

V
V

BAT
TS

< 0.25V

V

TS

< 2V and

> 0.25V

V

T/ t or

V

> 2V or

BAT

< 0.25V

V

TS

Maximum Time Out

V

or

CC

Figure 2. bq2002D State Diagram

4.0V

Fast

LED =

Low

Battery Voltage

too High?

< 2V

V

BAT

CC

V

BAT

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

Battery

Temperature?

> 2V or

V

VTS > 0.6 VCC or
VTS < 0.25 V

V

BAT

VTS < 0.6 VCC and
VTS > 0.25 V

V

CC

BAT

< 2V and

CC

Off,

CC = Low

LED = Low

Off,

CC = Low

LED = Z

2V

>

Charge
Pending

V

BAT

V

CC

CC

> 2V

BAT

Trickle
LED =

Low

Trickle

LED = Z

2V

SD2002D.eps

Charge

Pending

V

BAT

V

> 2V

BAT

2V

SD2002T.eps

Figure 3. bq2002T State Diagram

3

bq2002D/T

OSC

Clock

Phase

Generator

TM

INH

Charge-Control

State Machine

Power-On

Reset

CC

Timing

Control

LED

Figure 4. Block Diagram

Note: This resistor-divider network input impedance to
end-to-end should be at least 200kΩ and less than 1 MΩ.

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 VSS. See

CC

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

V

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

HTF<VTS

HTF<VTS<VLTF

for the bq2002D where

V

LTF

V

= 0.25 ∗ VCC±5% (bq2002T only)

HTF

or

CC

=2V±5%

MCV

BAT<VMCV

= 0.4 ∗ VCC±5%

. The valid tempera

for the bq2002T and

Sample

History

T/ t

ALU

MCV

Check

BAT

Power

Down

Voltage

Reference

A to D

Converter

V

CC

HTF/

LTF

Check

TCO

Check

V

SS

TS

Bd2002TD.eps

If the battery voltage or temperature is outside of these
limits, the IC pulse-trickle charges until the tempera­ture 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:

n

Rate of temperature rise

n

Maximum voltage

n

Maximum temperature

n

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

-

bq2002T and V

TCO<VTS

TCO<VTS<VLTF

for the bq2002D.

Temperature Sampling

A sample is taken by averaging together 16 measure
ments taken 57µs apart. The resulting sample period
(18.18ms) filters out harmonics around 55Hz. This tech

-

for the

-

-

4