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.

Figure 10. Voltage Divider

Figure 12. Cascading MAX1044/ICL7660 for Increased Output Voltage

Figure 11. Combined Positive and Negative Converter

MAX1044

ICL7660

+

4

3

2

1

5

6

7

8

C2

10µF

C1

10µF

V+

VOUT = V+

1

2

LV

MAX1044

ICL7660

+

4

3

2

1

5

6

7

8

MAX1044

ICL7660

4

3

2

1

5

6

7

8

10µF

10µF

10µF

10µF

V+

10µF

10µF

VOUT = -n(V+)

MAX1044

ICL7660

4

3

2

1

5

6

7

8

1

2

3

+

+

MAX1044

ICL7660

+

4

3

VOUT = 2(V+) - 2VD

2

1

5

6

7

8

C4

C1

C2

V+

VOUT = -(V+)

C3

LV

MAX1044/ICL7660

Switched-Capacitor Voltage Converters

www.maximintegrated.com

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