NiCd/NiMH Battery

Fast-Charge Controllers

14

______________________________________________________________________________________

The voltage-slope, fast-charge termination circuitry

might become disabled if attempting to charge a

different number of cells than the number programmed.

The switching frequency (nominally 30kHz) can be

decreased by increasing the value of the capacitor

connected between CC and BATT-. Make sure that

the two capacitors connected to the CC node are

placed as close as possible to the CC pin on the

MAX712/MAX713 and that their leads are of minimum

length. The CC node is a high-impedance point, so do

not route logic lines near the CC pin. The circuit of

Figure 19 cannot service a load while charging.

Order the MAX713SWEVKIT-SO for quick evaluation of

the MAX712/MAX713 in switch-mode operation. For

more information on switch-mode operation and

ordering information for external components, order the

MAX713EVKIT data sheet.

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

C1 = 1

R3 = 10k

Ω,R4 = 15kΩ

T1, T2 = part #13A1002 (Alpha Thermistor: (800) 235-5445)

R5 omitted, T3 omitted, TLO = BATT-

11

6

5

0

200

600

1000

7

10

400

LOAD CURRENT (mA)

800

9

8

LOW PEAK

HIGH PEAK

120Hz

RIPPLE

Figure 11. Sony CD Player AC Adapter AC-96N Load

Characteristic, 9VDC 600mA

4.3

4.2

030

90

4.5

5.0

4.9

4.7

4.4

60

TIME (MINUTES)

4.8

4.6

∆V

∆t

CUTOFF

26

24

30

40

38

34

28

36

32

V

T

Figure 13. 3 NiMH Cells Charged with MAX712

10

8

0

200

600

12

18

400

LOAD CURRENT (mA)

800

16

14

HIGH PEAK

LOW PEAK

120Hz

RIPPLE

Figure 12. Panasonic Modem AC Adapter KX-A11 Load

Characteristic, 12VDC 500mA

4.3

4.2

030

90

4.5

5.0

4.9

4.7

4.4

60

TIME (MINUTES)

4.8

4.6

26

24

30

40

38

34

28

36

32

∆V

∆t

CUTOFF

V

T

Figure 14. NiMH Cells Charged with MAX713