Switched-Capacitor Voltage Converters
MAX1044/ICL7660
V+
1
2
C1
10µF
3
4
8
1
2
C1
3
4
8
V+
V
OUT
= -(V+)
C3
LV
6
5
V
OUT
= 2(V+) - 2V
D
MAX1044
ICL7660
LV
7
6
5
MAX1044
ICL7660
7
V
OUT
= 1 V+
2
C2
10µF
C2
C4
Figure 10. Voltage Divider
Figure 11. Combined Positive and Negative Converter
Positive Voltage Doubler
Figure 9 illustrates the recommended voltage doubler
circuit for the MAX1044/ICL7660. To reduce the voltage
drops contributed by the diodes (V
D
), use Schottky
diodes. For true voltage doubling or higher output cur-
rents, use the MAX660.
capacitors for the doubled positive voltage. This circuit
has higher output impedances 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 V
OUT
= -n(V+)
where n is the number of devices cascaded. The out-
put 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 cascaded
in this way, but output impedance rises dramatically.
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.
Voltage Divider
The voltage divider shown in Figure 10 splits the power
supply in half. A third capacitor can be added between
V+ and V
OUT
.
Combined Positive Multiplication and
Negative Voltage Conversion
Figure 11 illustrates this dual-function circuit.
Capacitors C1 and C3 perform the bucket and reser-
voir functions for generating the negative voltage.
Capacitors C2 and C4 are the bucket and reservoir
1
2
10µF
3
4
8
V+
1
2
8
1
2
10µF
3
4
8
MAX1044
ICL7660
7
6
5
10µF
MAX1044
ICL7660
7
6
5
MAX1044
ICL7660
7
6
5
V
OUT
= -n(V+)
3
4
1
2
3
10µF
10µF
10µF
Figure 12. Cascading MAX1044/ICL7660 for Increased Output Voltage
10
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