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Combined Negative Voltage Conversion and Positive Supply Doubling

1

2

3

4

8

7

6

5

TL7660

V+

C

2

D

1

D

2

C

1

+

-

+

-

C

3

+

-

C

4

+

-

V

= –(nV – V

)

OUT

IN

FDX

V

= (2V+) – (V

) – (V

)

OUT

FD1

FD2

Voltage Splitting

1

2

3

4

8

7

6

5

TL7660

+

-

+

-

V+

V–

+

-

50 µF

R

L1

R

L2

50 µF

50 µF

V

=

OUT

2

V+

V

TL7660

CMOS VOLTAGE CONVERTER

SCAS794 – JUNE 2006

APPLICATION INFORMATION (continued)

Figure 10 combines the functions shown in Figure 3 and Figure 9 to provide negative voltage conversion and

positive voltage doubling simultaneously. This approach would be, for example, suitable for generating +9 V and

reservoir, respectively, for the doubled positive voltage. There is a penalty in this configuration that combines

both functions, however, in that the source impedances of the generated supplies are somewhat higher, due to

the finite impedance of the common charge pump driver at terminal 2 of the device.

Figure 10. Combined Negative-Voltage Converter and Positive-Voltage Doubler

The bidirectional characteristics can also be used to split a higher supply in half (see Figure 11. The combined

load is evenly shared between the two sides. 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 6, 15 V can be converted (via 7.5 V, and –7.5 V) to a nominal

–15 V, although with rather high series output resistance (~250

Ω).

Figure 11. Splitting a Supply in Half

13

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