Features

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

Direct LED output displays
charge status

Fast-charge termination by -

maximum voltage, maximum
temperature, and maximum
time

Internal band-gap voltage ref-
erence

Optional top-off charge

Selectable pulse trickle charge
rates

Low-power mode

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

General Description

The bq2002 and bq2002/F Fast-Charge
ICs are low-cost CMOS battery-charge
controllers providing reliable charge
termination for both NiCd and NiMH
battery applications.

Controlling a

current-limited or constant-current
supply allows the bq2002/F to be the
basis for a cost-effective stand-alone or
system-integrated charger.

The

bq2002/F 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:

Peak voltage detection (PVD)

Negative delta voltage (-

Maximum voltage

Maximum temperature

Maximum time

After fast charge, the bq2002/F op-
tionally tops-off and pulse-trickles the
battery per the pre-configured limits.
Fast charge may be inhibited using
the INH pin. The bq2002/F may also
be placed in low-standby-power mode
to reduce system power consumption.

T h e b q 2 0 0 2 F d i f f e r s f r o m t h e
bq2002 only in that a slightly differ-
ent set of fast-charge and top-off
time limits is available. All differ-
ences between the two ICs are illus-
trated in Table 1.

NiCd/NiMH Fast-Charge Management ICs

bq2002/F

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

bq2002/F Selection Guide

Part No.

TCO

HTF

LTF

V PVD Fast Charge

MTO

Top-Off

Maintenance

bq2002

0.5

None

C/2

160

C/32

C/64

C/16

C/64

None

C/32

bq2002F 0.5

None

C/2

160

C/32

C/64

100

C/16

C/64

None

C/32

SLUS131�JANUARY 1999 D

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

Figure 2 shows a state diagram and Figure 3 shows a
block diagram of the bq2002/F.

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.

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
thermistor placed near the battery may be used as a low-
cost temperature-to-voltage transducer. The temperature
sense voltage input at TS is developed using a resistor-
thermistor network between V

and V

. See Figure 1.

bq2002/F

Fg2002/F01.eps

bq2002/F

BAT

VSS

N
T
C

bq2002/F

VCC

PACK +

VSS

BAT pin connection

Thermistor connection

NTC = negative temperature coefficient thermistor.

RB1

RB2

Mid-level

setting for TM

Figure 1. Voltage and Temperature Monitoring and TM Pin Configuration

Starting A Charge Cycle

Either of two events starts a charge cycle (see Figure 4):

1. Application of power to V

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

MCV

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

> V

TCO

where

TCO

= 0.5

�5%.

If the battery voltage or temperature is outside of these
limits, the IC pulse-trickle charges until the next new
charge cycle begins.

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

Peak voltage detection (PVD)

Negative delta voltage (-

Maximum voltage

Maximum temperature

Maximum time

bq2002/F

Corresponding

Fast-Charge

Rate

Termination

Typical Fast-Charge

and Top-Off

Time Limits

(minutes)

Typical PVD

and -

V Hold-Off

Time (seconds)

Top-Off

Rate

Pulse-

Trickle

Rate

Pulse-

Trickle

Period

(ms)

bq2002

bq2002F

C/2

Mid

PVD

160

600

C/32

C/64

9.15

Low

PVD

100

300

C/16

C/64

18.3

High

150

Disabled

C/32

18.3

Notes:

Typical conditions = 25�C, V

= 5.0V.

Mid = 0.5 * V

�5V

Tolerance on all timing is

�20%.

Table 1. Fast-Charge Safety Time/Hold-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)

286

See

Table 1

286

4576

Figure 4. Charge Cycle Phases

PVD and -

V Termination

There are two modes for voltage termination depending
on the state of TM. For -

V (TM = high), if V

BAT

lower than any previously measured value by 12mV
�3mV, fast charge is terminated. For PVD (TM = low or
mid), a decrease of 2.5mV

�2.5mV terminates fast

charge. The PVD and -

V tests are valid in the range

1V < V

BAT

< 2V.

Voltage Sampling

Voltage is sampled at the BAT pin for PVD and -

V ter-

mination once every 17s. The sample is an average of
voltage measurements taken 57

�s apart. The IC takes

32 measurements in PVD mode and 16 measurements
in -

V mode. The resulting sample periods (9.17 and

18.18ms, respectively) filter out harmonics centered
around 55 and 109Hz. This technique minimizes the ef-
fect of any AC line ripple that may feed through the
power supply from either 50 or 60Hz AC sources. Toler-
ance on all timing is

�20%.

Voltage Termination Hold-off

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

V terminations

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

Maximum

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

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

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

Top-off Charge

An optional top-off charge phase may be selected to
follow fast charge termination for 1C and C/2 rates.
This phase may be necessary on NiMH or other bat-
tery 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 selected
by the TM pin. (See Table 1.) During top-off, the CC

pin is modulated at a duty cycle of 286

�s active for

every 4290

�s inactive. This modulation results in an

average rate 1/16th that of the fast charge rate. Maxi-
mum voltage, time, and temperature are the only ter-
mination methods enabled during top-off.

Pulse-Trickle Charge

Pulse-trickle is used to compensate for self-discharge
while the battery is idle in the charger. The battery is
pulse-trickle charged by driving the CC pin active for a
period of 286

�s for every 18.0ms of inactivity for 1C and

2C selections, and 286

�s for every 8.86ms of inactivity

for C/2 selection. This results in a trickle rate of C/64
for the top-off enabled mode and C/32 otherwise.

TM Pin

The TM pin is a three-level pin used to select the
charge timer, top-off, voltage termination mode, trickle
rate, and voltage hold-off period options. Table 1 de-
scribes the states selected by the TM pin. The mid-
level selection input is developed by a resistor di-
vider between V

and ground that fixes the voltage

on TM at V

� 0.5V. See Figure 4.

Charge Status Indication

A fast charge in progress is uniquely indicated when the
LED pin goes low. The LED pin is driven to the high-Z
state for all conditions other than fast charge. Figure 2
outlines the state of the LED pin during charge.

Charge Inhibit

Fast charge and top-off may be inhibited by using the
INH pin. When high, INH suspends all fast charge and
top-off activity and the internal charge timer.

INH

freezes the current state of LED until inhibit is re-
moved. Temperature monitoring is not affected by the
INH pin. During charge inhibit, the bq2002/F continues
to pulse-trickle charge the battery per the TM selection.
When INH returns low, charge control and the charge
timer resume from the point where INH became active.

Low-Power Mode

The IC enters a low-power state when V

BAT

is driven

above the power-down threshold (V

) where

= V

- (1V

�0.5V)

Both the CC pin and the LED pin are driven to the
high-Z state. The operating current is reduced to less
than 1

�A in this mode. When V

BAT

returns to a value

below V

, the IC pulse-trickle charges until the next

new charge cycle begins.

bq2002/F

Электронный компонент: BQ2002