Data Sheet
ICL7660S, ICL7660A
FN3179 Rev 7.00 Page 11 of 13
January 23, 2013
Voltage Splitting
The bidirectional characteristics can also be used to split a
high supply in half, as shown in Figure 20. The combined load
will be evenly shared between the two sides, and a high value
resistor to the LV pin ensures start-up. Because the switches
share the load in parallel, the output impedance is much lower
than in the standard circuits, and higher currents can be drawn
from the device. By using this circuit, and then the circuit of
Figure 15, +15V can be converted, via +7.5 and -7.5, to a
nominal -15V, although with rather high series output
resistance (
250).
Regulated Negative Voltage Supply
In some cases, the output impedance of the ICL7660S and
ICL7660A can be a problem, particularly if the load current
varies substantially. The circuit of Figure 21 can be used to
overcome this by controlling the input voltage, via an ICL7611
low-power CMOS op amp, in such a way as to maintain a
nearly constant output voltage. Direct feedback is inadvisable,
since the ICL7660S’s and ICL7660A’s output does not respond
instantaneously to change in input, but only after the switching
delay. The circuit shown supplies enough delay to
accommodate the ICL7660S and ICL7660A, while maintaining
adequate feedback. An increase in pump and storage
capacitors is desirable, and the values shown provide an
output impedance of less than 5 to a load of 10mA.
Other Applications
Further information on the operation and use of the ICL7660S
and ICL7660A may be found in application note AN051,
“Principles and Applications of the ICL7660 CMOS Voltage
Converter”.
1
2
3
4
8
7
6
5
ICL7660S
V+
D
1
D
2
C
4
V
OUT
= (2V+) -
(V
FD1
) - (V
FD2
)
+
-
C
2
+
-
C
3
+
-
V
OUT
= -V
IN
C
1
+
-
FIGURE 19. COMBINED NEGATIVE VOLTAGE CONVERTER
AND POSITIVE DOUBLER
D
3
ICL7660A
1
2
3
4
8
7
6
5
+
-
+
-
50µF
50µF
+
-
50µF
R
L1
V
OUT
=
V+ - V-
2
ICL7660S
V+
V-
R
L2
FIGURE 20. SPLITTING A SUPPLY IN HALF
ICL7660A
1
2
3
4
8
7
6
5
+
-
100µF
ICL7660S
100µF
V
OUT
+
-
10µF
ICL7611
+
-
100
50k
+8V
100k
50k
ICL8069
56k
+8V
800k
250k
VOLTAGE
ADJUST
+
-
FIGURE 21. REGULATING THE OUTPUT VOLTAGE
ICL7660A