MAX712 Maxim, MAX712 Datasheet - Page 15

• Manufacturer Part Number: MAX712
• Description: NiCd/NiMH Battery Fast-Charge Controllers
• Manufacturer: Maxim

The absolute maximum voltage rating for the BATT+ pin
is higher when the MAX712/MAX713 are powered on. If
more than 11 cells are used in the battery, the BATT+
input voltage must be limited by external circuitry when
DC IN is not applied (Figure 15).
The current-sense resistor, R
efficiency loss during battery use. The efficiency loss is
Figure 15. Cascoding to Accommodate High Cell Counts for
Linear-Mode Circuits
Figure 16. Shunting R
DC IN
V+
MAX712
MAX713
MAX712
MAX713
100k
Linear-Mode, High Series Cell Count
D1
150
R2
______________________________________________________________________________________
100k
500
Efficiency During Discharge
SENSE
GND
DRV
Q1
for Efficiency Improvement
BATT+
*
SENSE
33k
D1
, causes a small
R
SENSE
>4 CELLS
Q2
*
LOW R
LOGIC LEVEL
N-CHANNEL
POWER
MOSFET
TERMINAL
BATTERY
POSITIVE
TO
ON
Fast-Charge Controllers
significant only if R
battery stack’s internal resistance. The circuit in Figure
16 can be used to shunt the sense resistor whenever
power is removed from the charger.
Figure 17 shows a circuit that can be used to indicate
charger status with logic levels. Figure 18 shows a
circuit that can be used to drive LEDs for power and
charger status.
Figure 17. Logic-Level Status Outputs
Figure 18. LED Connection for Status Outputs
DC IN
MAX712
MAX713
MAX712
MAX713
MAX712
MAX713
NiCd/NiMH Battery
FASTCHG
FASTCHG
V+
V+
SENSE
10k
is much greater than the
470 MIN
R1
Status Outputs
OV = NO POWER
5V = POWER
V
OV = FAST
V
NO POWER
CC
CC
= TRICKLE OR
FAST CHARGE
CHARGE POWER
15