NiCd/NiMH Battery

Fast-Charge Controllers

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13

Some battery packs come with a temperature-detect-

ing thermistor connected to the battery pack’s negative

terminal. In this case, use the configuration shown in

Figure 9b. Thermistors T2 and T3 can be replaced by

standard resistors if absolute temperature charge cut-

off is acceptable. All resistance values in Figures 9a

and 9b should be chosen in the 10k

Ω to 500kΩ range.

__________Applications Information

Battery-Charging Examples

Figures 13 and 14 show the results of charging 3 AA,

1000mAh, NiMH batteries from Gold Peak (part no.

GP1000AAH, GP Batteries (619) 438-2202) at a 1A rate

using the MAX712 and MAX713, respectively. The

Typical Operating Circuit is used with Figure 9a’s

thermistor configuration .

DC IN = Sony AC-190 +9VDC at 800mA AC-DC adapter

PGM0 = V+, PGM1 = REF, PGM2 = REF, PGM3 = REF

R1 = 200

R3 = 10k

Ω, R4 = 15kΩ

T1, T2 = part #14A1002 (Alpha Sensors: 858-549-4660) R5

omitted, T3 omitted, TLO = BATT-

0.022

μF

0.022

μF

NOTE: FOR ABSOLUTE TEMPERATURE CHARGE CUTOFF, T2 AND T3 CAN BE

REPLACED BY STANDARD RESISTORS.

1

μF

TEMP

TLO

IN THERMAL

CONTACT WITH

BATTERY

AMBIENT

TEMPERATURE

AMBIENT

TEMPERATURE

T3

+2.0V

T2

T1

R3

R4

R5

HOT

REF

THI

BATT-

COLD

MAX712

MAX713

Figure 9a. Temperature Comparators

MAX712

MAX713

0.022

μF

0.022

μF

NOTE: FOR ABSOLUTE TEMPERATURE CHARGE CUTOFF, T2 AND T3 CAN BE

REPLACED BY STANDARD RESISTORS.

1

μF

TEMP

TLO

AMBIENT

TEMPERATURE

AMBIENT

TEMPERATURE

IN THERMAL

CONTACT WITH

BATTERY

T3

+2.0V

T1

T2

R4

R3

R5

HOT

REF

THI

BATT-

COLD

Figure 9b. Alternative Temperature Comparator Configuration

11

6

0

200

600

1000

7

10

400

800

9

8

120Hz RIPPLE

LOW PEAK

HIGH PEAK

LOAD CURRENT (mA)

Figure 10. Sony Radio AC Adapter AC-190 Load Characteristic,

9VDC 800mA