TEXAS INSTRUMENTS bq2002E, bq2002G Technical data

bq2002E/G

NiCd/NiMH Fast-Charge Management ICs

Features

Fast charge of nickel cadmium

➤

or nickel-metal hydride batter
ies

Direct LED output displays

➤

chargestatus
Fast-charge terminationby -∆V,

➤

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

Pin Connections

TM

LED

BAT
V

SS

1

2

3

4

8

7

6

5

CC

INH

V
TS

CC

General Description

The bq2002E a n d bq2002G Fast­Charge ICs are low-cost CMOS bat

­tery-charge controllers providing reli
able charge termination for both NiCd
and NiMH battery applications. Co n
trolling a current-limited or con
stant-current supply allows th e
bq2002E/G to be the basis for a cost­effective 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. Fo r 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:

Peak voltage detection(PVD)

n

-

­Negative delta voltage(-∆V)

n

-

Maximum voltage

n

­Maximum temperature

n

Maximum time

n

-

-

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.
The bq2002E differs from the

bq2002G only in that a slightly dif­ferent se t of fast-charge and top-off
time limits is available. All differ­ences between the two ICs are illus­trated in Table 1.

TS Temperature senseinput
V

CC

Supply voltage input
INH Charge inhibit input
CC Charge control output

-

8-Pin DIP or

Narrow SOIC

PN-200201.eps

bq2002E/G Selection Guide

Part No. LBAT TCO HTF LTF

bq2002E

bq2002G

SLUS132 - FEBRUARY 1999

0.175
V

0.175
V

∗

0.5

∗

0.6

V

CC

CC

CC

∗

0.5

∗

V

CC

V

0.6
V

∗

CC

∗

CC

None

None

PVD Fast Charge t

-∆V

✔
✔

✔

✔
✔

✔

1

MTO

Top-Off Maintenance

C/2 200 None C/32

1C 80 C/16 C/32
2C 40 None C/32

C/2 160 None C/32

1C 80 C/16 C/32
2C 40 None C/32

bq2002E/G

Pin Descriptions

TM

LED

BAT

V

SS

TS

V

CC

INH

T ime rmodeinput

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

Thebattery 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.

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,
ifenabled,and pulse trickle.

Functional Description

Figure 2 shows a state diagram and Figure 3 shows a
block diagram ofth e bq2002E/G.

-

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-dividerratio of

RB1

= N - 1

RB2

is recommended to maintain the battery voltage within
the valid range, where N is th e number of cells, RB1 is
the resistor connected to the positive battery terminal,
and RB2 is the resistor connected to the negative bat­tery terminal. SeeFigure 1.

Note:

This resistor-divider network input impedance to

end-to-end should be at least 200k

Ω

and less than 1MΩ.

-

V

CC

RT

BAT

bq2002E/G

V

BAT pin connection Thermistor connection

RB1

RB2

SS

NTC = negative temperature coefficient thermistor.

R3

R4

Mid-level

setting for TM

V

CC

TM

bq2002E/G

V

T

S

SS

PACK +

N
T
C

Fg2002E/G01.eps

Figure 1. Voltage and Temperature Monitoring and TM Pin Configuration

2

bq2002E/G

V or

(PVD or ­Maximum Time Out)
and TM = Low

Top-off

LED = Z

V

2V or

BAT

V

VCC/2 or

TS

Maximum Time Out

OSC

V

CC

Chip on

4.0V

V

TS

Battery Voltage

too High?

< 2V

V

BAT

Battery Voltage

too Low?

V

0.175

> 0.6

< V

CC

V

CC

Fast

LED =

Low

V

> 2V or

BAT

VTS < VCC/2 or
((PVD or - V or
Maximum Time Out)
and TM

BAT

Battery

Temperature?

Low)

Figure 2. State Diagram

Clock

Phase

Generator

V
V
V

BAT
BAT
TS

V

BAT

V

BAT

V

TS

> 0.175
< 2V, and

> V

CC

2V

>

< 0.175

< 0.6

/2

VCC,

V

V

CC

CC

Trickle

LED =

Flash

Trickle

LED = Z

Charge
Pending

V

BAT

V

> 2V

BAT

2V

2

SD

s

p

.e

2C

00

TM

INH

Charge-Control

State Machine

Power-On

Reset

Timing

Control

Sample

History

PVD, - V

ALU

HTF

Check

CC

LED

Figure 3. Block Diagram

3

TCO

Check

TS

Power

Down

Voltage

Reference

A to D

Converter

LBAT

Check

MCV

Check

V

CC

V

SS

Bd2002CEG.eps

BAT

bq2002E/G

Fast ChargingVCC = 0 Fast Charging

(optional)

CC Output

73ms

1.17s 1.17s

Charge initiated by application of power

LED

Figure 4. Charge Cycle Phases

Aground-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 resistor­thermistor network between V

and VSS. See Figure 1.

CC

Starting A Charge Cycle

Either of twoevents starts a chargecycle(see Figure 4):

Pulse-TrickleTop-Off

See Table 1

Charge initiated by battery replacement

1.Application ofpower to V

or

CC

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

MCV

where

V

MCV

= 2V±5%.

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

LBAT<VBAT<VMCV

,where

TD2002EG.eps

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

Typical Fast-

Charge and

-

Corre

sponding

Fast-Charge

Rate TM Termination

Time Limits

(minutes)

bq2002E bq2002G

Typical PVD

and -∆V

Hold-Off Time

(seconds)

Top-Off

Rate

Pulse­Trickle

Rate

C/2 Mid PVD 200 160 300 Disabled C/32 73 18.7

1C Low PVD 80 80 150 C/16 C/32 37 18.7

Top-Off

2C High -

Notes:

Typical conditions = 25°C, VCC= 5.0V
Mid = 0.5*V
Tolerance on all timing is

V 40 40 75 Disabled C/32 18 9.4

∆

0.5V

±

CC

±

12%.

4

Pulse-

Trickle

Width

(ms)

Maximum

Synchro

nized

Sampling

Period

(seconds)

-

bq2002E/G

V

= 0.175∗VCC±

LBAT

The valid temperature range isV

= 0.6∗VCC±

V

HTF

20%

TS>VHTF

5%.

where

If the battery voltage or temperature is outside of these
limits, th e IC pulse-trickle charges until the next new
chargecyclebegins.

If V

MCV<VBAT<VPD

newbattery is inserted, a delay of0.35 to 0.9s is imposed

(see “Low-Power Mode”) when a

before the new charge cyclebegins.
Fast charge continues until termination by one or more of

the five possible termination conditions:

Peak voltage detection (PVD)

n

Negative delta voltage (-∆V)

n

Maximum voltage

n

Maximum temperature

n

Maximum time

n

PVD and -∆V Termination

There are two modes for voltage termination, depending
on the state ofTM. For ­than any previously measured value by 12mV

∆

V (TM = high), if V

is lower

BAT

±

3mV, fast
charge is terminated. For PVD (TM = low or mid), a de­crease of 2.5mV
and -

∆

Vtests are valid in the range 1V<V

±

2.5mV terminates fast charge. The PVD

BAT

<2V.

Synchronized Voltage Sampling

Voltage sampling at the BAT pin for PVD and -∆Vtermi
nation may be synchronized to an external stimulus us­ing the INH input. Low-high-low input pulses between
100ns a nd 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 edgeofsuch 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
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 50or60Hz ACsources.

If the INH input remains high for more than 12ms, the
voltage sample history kept by the IC a nd 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.

µ

s apart. The IC takes

The response of the IC to pulses less than 100ns i n
width or between 3.5ms and 12ms is indeterminate. Tol

±

erance on all timing is

12%.

Voltage TerminationHold-off

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

∆

Vterminations
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 BA T pin exceeds the maxi
mum cell voltage,V
chargeis terminated.

Maximum temperature termination occurs anytime t h e
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 a re available for corresponding charge
rates of C/2, 1C, and 2C. Maximum time-out termina­tion is enforced on the fast-charge phase, then reset, and
enforced again on the top-off phase, if selected. There is
notime limit onthe trickle-charge phase.

, fast charge or optional top-off

MCV

where

V

TCO

= 0.5∗VCC±

5%.

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 ba t-

tery chemistries that have a tendency to terminate
charge before reaching full capacity. With top-off en
abled, charging continues at a r educed ra te after

­fast-charge termination for a period of time selected

by t h e 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 a n

-

average rate 1/16th that ofthe fast charge rate. Maxi
mum voltage, time, an d 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 ofC/32.

TM Pin

­The TM pin is a three-level pin used to select th e

­chargetimer,top-off, voltage termination mode, trickle

-

-

-

-

-

-

5