Features

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

Direct LED o u t p u t displays
charge status

Fast-charge termination by -

maximum voltage, maximum
t e m p e r a t u r e, a n d 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 bq2002E and bq2002G Fast-
Charge ICs are low-cost CMOS bat-
tery-charge controllers providing reli-
able charge termination for both NiCd
and NiMH battery applications. Con-
trolling a current-limited or con-
s t a n t - c u r r e n t supply allows t h e
bq2002E/G to be the basis for a cost-
effective stand-alone or system-inte-
grated charger. The bq2002E/G inte-
grates fast charge with optional top-off
and pulsed- trickle control 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 bq2002E/G op-
tionally tops-off and pulse-trickles the
battery per the pre-configured limits.
Fast charge may be inhibited using
the INH pin.

The bq2002E/G may

also be placed in low-standby-power
mode to reduce system power con-
sumption.

T h e b q 2 0 0 2 E d i f f e r s f r o m t h e
bq2002G only in that a slightly dif-
ferent 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

bq2002E/G

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

SLUS132 - FEBRUARY 1999

bq2002E/G Selection Guide

Part No.

LBAT

TCO

HTF

LTF

PVD

Fast Charge

MTO

Top-Off

Maintenance

bq2002E 0.175

0.5

0.6

None

C/2

200

None

C/32

C/16

C/32

None

C/32

bq2002G 0.175

0.5

0.6

None

C/2

160

None

C/32

C/16

C/32

None

C/32

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 t he
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 bq2002E/G.

Battery Voltage and Temperature
Measurements

Battery voltage and temperature are monitored for
maximum allowable values. The voltage presented on
t h e b a t t e r y 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

bq2002E/G

Fg2002E/G01.eps

bq2002E/G

BAT

VSS

N
T
C

bq2002E/G

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

A ground-referenced negative temperature coefficient ther-
mistor 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.

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

LBAT

< V

BAT

< V

MCV

, where

bq2002E/G

Corre-

sponding

Fast-Charge

Rate

Termination

Typical Fast-

Charge and

Top-Off

Time Limits

(minutes)

Typical PVD

and -

Hold-Off Time

(seconds)

Top-Off

Rate

Pulse-

Trickle

Rate

Pulse-

Trickle

Width

(ms)

Maximum

Synchro-

nized

Sampling

Period

(seconds)

bq2002E bq2002G

C/2

Mid

PVD

200

160

300

Disabled

C/32

18.7

Low

PVD

150

C/16

C/32

18.7

High

Disabled

C/32

9.4

Notes:

Typical conditions = 25°C, V

= 5.0V

Mid = 0.5 * V

0.5V

Tolerance on all timing is

12%.

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

TD2002EG.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)

73ms

1.17s

See Table 1

Figure 4. Charge Cycle Phases

LBAT

= 0.175

20%

The valid temperature range is V

> V

HTF

where

HTF

= 0.6

5%.

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

If V

MCV

< V

BAT

< V

(see "Low-Power Mode") when a

new battery is inserted, a delay of 0.35 to 0.9s is imposed
before the 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

PVD and -

V Termination

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

V (TM = high), if V

BAT

is lower

than any previously measured value by 12mV

3mV, fast

charge is terminated. For PVD (TM = low or mid), a de-
crease of 2.5mV

2.5mV terminates fast charge. The PVD

and -

V tests are valid in the range 1V < V

BAT

< 2V.

Synchronized Voltage Sampling

Voltage sampling at the BAT pin for PVD and -

V termi-

nation may be synchronized to an external stimulus us-
ing the INH input. Low-high-low input pulses between
100ns and 3.5ms in width must be applied at the INH
pin with a frequency greater than the "maximum syn-
chronized sampling period" set by the state of the TM
pin as shown in Table 1. Voltage is sampled on the fal-
ling edge of such pulses.

If the time between pulses is greater than the synchro-
nizing period, voltage sampling "free-runs" at once every
17 seconds.

A sample is taken by averaging together

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.

If the INH input remains high for more than 12ms, the
voltage sample history kept by the IC and used for PVD
and -

V termination decisions is erased and a new his-

tory is started. Such a reset is required when transition-
ing from free-running to synchronized voltage sampling.

The response of the IC to pulses less than 100ns in
width or between 3.5ms and 12ms is indeterminate. Tol-
erance on all timing is

12%.

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

where

TCO

= 0.5

5%.

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 before reaching full capacity. With top-off en-
abled, ch arging continues a t a r educed r a t e 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 73ms active for

every 1097ms 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 once
every 1.17s for the period specified in Table 1. This re-
sults in a trickle rate of C/32.

TM Pin

The TM pin is a three-level pin used to select the
charge timer, top-off, voltage termination mode, trickle

bq2002E/G

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