Datasheet

MAX712/MAX713
NiCd/NiMH Battery
Fast-Charge Controllers
______________________________________________________________________________________ 13
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 10kΩto 500kΩrange.
__________Applications Information
Switch-Mode Operation
For applications where the power dissipation in the
pass transistor cannot be tolerated (ie., where heat
sinking is not feasible or is too costly), a switch-mode
charger is recommended.
Switch-mode operation can be implemented simply by
using the circuit of Figure 19. The circuit of Figure 19
uses the error amplifier at the CC pin as a comparator
with the 33pF capacitor adding hysteresis. Figure 19 is
shown configured to charge two cells at 1A. Lower
charge currents and a different number of cells can be
accommodated simply by changing R
SENSE
and
PGM0–PGM3 connections (Tables 2 and 3).
The input power-supply voltage range is 8V to 15V and
must be at least 2V greater than the peak battery
voltage, under fast charge. As shown in Figure 19, the
source should be capable of greater than 1.3A of
output current. The source requirements are critical
because if violated, proper termination of the fast-
charge cycle might not occur. For input voltages
greater than 15V, see the MAX713SWEVKIT data sheet.
MAX712
MAX713
0.022µF
0.022µF
NOTE: FOR ABSOLUTE TEMPERATURE CHARGE CUTOFF, T2 AND T3 CAN BE
REPLACED BY STANDARD RESISTORS.
1µF
TEMP
TLO
IN THERMAL
CONTACT WITH
BATTERY
AMBIENT
TEMPERATURE
AMBIENT
TEMPERATURE
T3
+2.0V
T2
T1
R3
R4
R5
HOT
REF
THI
BATT-
COLD
Figure 9a. Temperature Comparators
MAX712
MAX713
0.022µF
0.022µF
NOTE: FOR ABSOLUTE TEMPERATURE CHARGE CUTOFF, T2 AND T3 CAN BE
REPLACED BY STANDARD RESISTORS.
1µF
TEMP
TLO
AMBIENT
TEMPERATURE
AMBIENT
TEMPERATURE
IN THERMAL
CONTACT WITH
BATTERY
T3
+2.0V
T1
T2
R4
R3R5
HOT
REF
THI
BATT-
COLD
Figure 9b. Alternative Temperature Comparator Configuration
11
6
0 200 600 1000
7
10
MAX712/713
OUTPUT VOLTAGE (V)
400
LOAD CURRENT (mA)
800
9
8
120Hz RIPPLE
LOW PEAK
HIGH PEAK

Figure 10. Sony Radio AC Adapter AC-190 Load Characteristic,
9VDC 800mA