NiCd/NiMH Battery

Fast-Charge Controllers

______________________________________________________________________________________

15

Linear-Mode, High Series Cell Count

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).

Efficiency During Discharge

efficiency loss during battery use. The efficiency loss is

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.

Status Outputs

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.

Q1

D1

R2

150

Ω

DC IN

33k

Q2

500

Ω

DRV

BATT+

TO

BATTERY

POSITIVE

TERMINAL

MAX712

MAX713

Figure 15. Cascoding to Accommodate High Cell Counts for

Linear-Mode Circuits

100k

100k

MAX712

MAX713

D1

V+

GND

>4 CELLS

LOGIC LEVEL

N-CHANNEL

POWER

MOSFET

*

*

10k

OV = NO POWER

5V = POWER

OV = FAST

NO POWER

MAX712

MAX713

V+

FASTCHG

MAX712

MAX713

Figure 17. Logic-Level Status Outputs

V+

MAX712

MAX713

R1

470

ΩMIN

FASTCHG

DC IN

CHARGE POWER

FAST CHARGE

Figure 18. LED Connection for Status Outputs