MAX1044/ICL7660
Switched-Capacitor Voltage Converters
Positive Voltage Doubler
Figure 9 illustrates the recommended voltage doubler
circuit for the MAX1044/ICL7660. To reduce the volt-
age drops contributed by the diodes (VD), use Schottky
diodes. For true voltage doubling or higher output cur-
rents, use the MAX660.
Voltage Divider
The voltage divider shown in Figure 10 splits the power
supply in half. A third capacitor can be added between V+
and VOUT.
Combined Positive Multiplication and
Negative Voltage Conversion
Figure 11 illustrates this dual-function circuit. Capacitors
C1 and C3 perform the bucket and reservoir functions for
generating the negative voltage. Capacitors C2 and C4
are the bucket and reservoir capacitors for the doubled
positive voltage. This circuit has higher output imped-
ances resulting from the use of a common charge-pump
driver.
Cascading Devices
Larger negative multiples of the supply voltage can
be obtained by cascading MAX1044/ICL7660 devices
(Figure 12). The output voltage is nominally VOUT =
-n(V+) where n is the number of devices cascaded. The
output voltage is reduced slightly by the output resistance
of the first device, multiplied by the quiescent current
of the second, etc. Three or more devices can be cas-
caded in this way, but output impedance rises dramati-
cally. For example, the output resistance of two cascaded
MAX1044s is approximately five times the output resis-
tance of a single voltage converter. A better solution may
be an inductive switching regulator, such as the MAX755,
MAX759, MAX764, or MAX774.
C1
10µF
VOUT =
1 V+
2
+
1
2
MAX1044
ICL7660
3
V+
8
7
6
4
LV 5
C2
10µF
Figure 10. Voltage Divider
+
V+
1
8
2
MAX1044
7
ICL7660
C1
3
LV 6
VOUT = -(V+)
C3
4
5
VOUT = 2(V+) - 2VD
C2
C4
Figure 11. Combined Positive and Negative Converter
+
+
+
1
8 V+
1
8
1
8
MAX1044
2
ICL7660
7
MAX1044
2
ICL7660
7
MAX1044
2
ICL7660
7
10µF
3
4
1
6 10µF
3
5
4
6 10µF
3
5
4
2
6
5 VOUT = -n(V+)
3
10µF
10µF
10µF
Figure 12. Cascading MAX1044/ICL7660 for Increased Output Voltage
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