Increasing Output Voltage

Stacking the LMC7660s is an easy way to produce a greater

negative voltage. It should be noted that the input current re-

quired for each stage is twice the load current on that stage

as shown in

Figure 6. The effective output resistance is ap-

proximately the sum of the individual R

only a few levels of multiplication can be used.

It is possible to generate −15V from +5V by connecting the

second 7660’s pin 8 to +5V instead of ground as shown in

Figure 7. Note that the second 7660 sees a full 20V and the

input supply should not be increased beyond +5V.

Split V

Figure 8 is one of the more interesting applications for the

LMC7660. The circuit can be used as a precision voltage di-

vider (for very light loads), alternately it is used to generate a

1

S1 and S3 are closed, the supply voltage divides across the

capacitors in a conventional way proportional to their value.

switch from a series connection to a parallel connection. This

forces the capacitors to have the same voltage; the charge

redistributes to maintain precisely V

this application all devices are only V

age can be raised to 20V giving exactly 10V at V

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FIGURE 5. Lowering Output Resistance by Paralleling Devices

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FIGURE 6. Higher Voltage by Cascade

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FIGURE 7. Getting −15V from +5V

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