MAX712 Maxim, MAX712 Datasheet - Page 13

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

Figure 9a. Temperature Comparators
Figure 9b. Alternative Temperature Comparator Configuration
NOTE: FOR ABSOLUTE TEMPERATURE CHARGE CUTOFF, T2 AND T3 CAN BE
REPLACED BY STANDARD RESISTORS.
NOTE: FOR ABSOLUTE TEMPERATURE CHARGE CUTOFF, T2 AND T3 CAN BE
REPLACED BY STANDARD RESISTORS.
+2.0V
+2.0V
COLD
COLD
HOT
HOT
MAX712
MAX713
MAX712
MAX713
______________________________________________________________________________________
BATT-
TEMP
TLO
REF
THI
BATT-
TEMP
TLO
REF
THI
R3
R4
CONTACT WITH
0.022µF
IN THERMAL
TEMPERATURE
BATTERY
AMBIENT
0.022µF
TEMPERATURE
T2
0.022µF
T1
R5
AMBIENT
TEMPERATURE
TEMPERATURE
T3
CONTACT WITH
AMBIENT
IN THERMAL
AMBIENT
R5
BATTERY
0.022µF
1µF
T3
R3
R4
T1
T2
1µF
Fast-Charge Controllers
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 to 500k range.
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
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.
Figure 10. Sony Radio AC Adapter AC-190 Load Characteristic,
9VDC 800mA
__________Applications Information
NiCd/NiMH Battery
11
10
9
8
7
6
0
200
LOAD CURRENT (mA)
Switch-Mode Operation
400
LOW PEAK
HIGH PEAK
600
120Hz RIPPLE
800
SENSE
1000
and
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