BQ2002FSNTRG4 Datasheet, PDF (2/17 Pages) Texas Instruments – NiCd/NiMH Fast-Charge Management ICs

bq2002/F
Pin Descriptions
TM
LED
BAT
VSS
TS
VCC
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
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,
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. A
resistor-divider ratio of
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 bat-
tery terminal. See Figure 1.
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
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 VCC and VSS. See Figure 1.
RB1
BAT
bq2002/F
RB2
VSS
VCC
RT
R3
VCC
TM
TS
R4
bq2002/F
VSS
PACK +
N
T
C
BAT pin connection
Mid-level
setting for TM
Thermistor connection
NTC = negative temperature coefficient thermistor.
Fg2002/F01.eps
Figure 1. Voltage and Temperature Monitoring and TM Pin Configuration
2