Positive Voltage Doubler

Figure 9 illustrates the recommended voltage doubler

circuit for the MAX1044/ICL7660. To reduce the voltage

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

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

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

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.

Switched-Capacitor Voltage Converters

10

______________________________________________________________________________________

MAX1044

ICL7660

4

3

2

1

5

6

7

8

C2

10µF

C1

10µF

V+

V+

1

2

LV

Figure 10. Voltage Divider

MAX1044

ICL7660

4

3

2

1

5

6

7

8

C4

C1

C2

V+

C3

LV

Figure 11. Combined Positive and Negative Converter

MAX1044

ICL7660

4

3

2

1

5

6

7

8

MAX1044

ICL7660

4

3

2

1

5

6

7

8

10µF

10µF

V+

10µF

10µF

10µF

10µF

MAX1044

ICL7660

4

3

2

1

5

6

7

8

12

3

Figure 12. Cascading MAX1044/ICL7660 for Increased Output Voltage