1
Features
➤ Safe charge of three or four re-
chargeable alkaline batteries
such as Renewal
®
from Rayovac
®
➤ Pulsed charge terminated with
maximum voltage limit
➤ LED outputs indicate charge
status
➤ Selectable end-of-discharge volt-
age prevents overdischarge and
improves cycle life
➤ Optional external FET drive al-
lows high current loads
➤ Pre-charge qualification indicates
fault conditions
➤ Automatic charge control simpli-
fies charger design
➤ Available in 14-pin 300-mil DIP
or 150-mil SOIC
General Description
The bq2903 is a cost-effective charge
controller for rechargeable alkaline
batteries such as Renewal batteries
from Rayovac. The bq2903 combines
sensitive, full-charge detection for
three to four rechargeable alkaline
cells, with a low-battery cut-off for
over-discharge protection.
Designed for integration into a three-
or four-cell system, the bq2903 can
improve the service life of the re-
chargeable alkaline cells by properly
managing the charge and discharge.
The bq2903 requires a voltage-limited
current source to generate the proper
charge pulses for the Renewal cell.
Each cell is individually monitored
to ensure full charge without a dam-
aging overcharge.
Charge completion is indicated when
the average charge rate falls below
approximately 6% of the fast charge
rate. Status outputs are provided to
indicate charge in progress, charge
complete, or fault condition.
The bq2903 avoids over-depleting
the battery by using the internal
end-of-discharge control circuitry.
The bq2903 also eliminates the ex-
ternal power switching transistors
needed to separately charge indi-
vidual Renewal cells.
To reduce external component count,
the discharge and charge control
FETs are internal to the bq2903;
however, if the discharge load is
greater than 400mA, a DRV pin is
provided to drive an external N-FET,
reducing the effective discharge path
resistance for the system.
For safety, charging is inhibited if the
voltage of any cell is greater than
3.0V during charge or if the voltage of
any cell is less than 0.4V when not
charging (open-circuit voltage).
bq2903
6/99 C
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PN290301.eps
14-Pin Narrow DIP
or SOIC
2
3
4
5
6
7
14
13
12
11
10
9
8
BAT
1P
DC
LRTN
2
V
SS
V
SS
LRTN
1
DRV
BAT
1N
BAT
2N
BAT
3N
N
SEL
V
SEL
DONE
CHG
DC Charging supply input
CHG Battery status output 1
DONE Battery status output 2
NSEL Number of cells input
VSEL End of discharge
voltage select input
BAT1P Battery 1 positive input
BAT1N Battery 1 negative input
BAT2N Battery 2 negative input
BAT3N Battery 3 negative input
VSS Battery 4 negative input/
IC ground
LRTN1, 2 System load returns
DRV External FET drive
output
Pin NamesPin Connections
Rechargeable Alkaline Charge/Discharge
Controller IC