NiCd /NiMH Ba t t e ry
Fa s t -Ch a rg e Co n t ro lle rs
2/MAX713
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.
IN THERMAL
CONTACT WITH
BATTERY
REF
THI
R3
R4
__________Ap p lic a t io n s In fo rm a t io n
T1
HOT
AMBIENT
TEMPERATURE
S w it c h -Mo d e Op e ra t io n
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.
0.022µF
R5
TEMP
TLO
+2.0V
COLD
T2
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
MAX712
MAX713
T3
1µF
0.022µF
BATT-
AMBIENT
TEMPERATURE
a c c ommod a te d s imp ly b y c ha ng ing R
a nd
SENSE
PGM0–PGM3 connections (Tables 2 and 3).
NOTE: FOR ABSOLUTE TEMPERATURE CHARGE CUTOFF, T2 AND T3 CAN BE
REPLACED BY STANDARD RESISTORS.
The input power-supply voltage range is 8V to 15V and
mus t b e a t le a s t 2V g re a te r tha n the p e a k b a tte ry
voltage, under fast charge. As shown in Figure 19, the
s ourc e s hould b e c a p a b le of g re a te r tha n 1.3A of
output current. The source requirements are critical
because if violated, proper termination of the fast-
c ha rg e c yc le mig ht not oc c ur. For inp ut volta g e s
greater than 15V, see the MAX713SWEVKIT data sheet.
Figure 9a. Temperature Comparators
AMBIENT
TEMPERATURE
REF
T2
THI
11
HOT
R5
R3
R4
+2.0V
TEMP
10
HIGH PEAK
1µF
COLD
9
TLO
0.022µF 0.022µF
120Hz RIPPLE
8
7
6
MAX712
MAX713
T1
T3
LOW PEAK
BATT-
IN THERMAL
CONTACT WITH
BATTERY
AMBIENT
TEMPERATURE
0
200
400
600
800
1000
NOTE: FOR ABSOLUTE TEMPERATURE CHARGE CUTOFF, T2 AND T3 CAN BE
REPLACED BY STANDARD RESISTORS.
LOAD CURRENT (mA)
Figure 9b. Alternative Temperature Comparator Configuration
Figure 10. Sony Radio AC Adapter AC-190 Load Characteristic,
9VDC 800mA
______________________________________________________________________________________ 13
MAXIM [ MAXIM INTEGRATED PRODUCTS ]
