Getting Up … and Down

The LMC7660 can also be used as a positive voltage multi-

plier. This application, shown in

Figure 9, requires 2 addi-

open and S1 is closed. Since C

is referenced to V

at V

application uses only two of the four switches in the 7660.

The other two switches can be put to use in performing a

negative conversion at the same time as shown in

Figure 10.

from ground to −V

charge. In the interval that S1 and S3 are closed, C

the junction of D1 and D2 above V

from V

Thermometer Spans 180˚C

Using the combined negative and positive multiplier of

Fig-

ure 11 with an LM35 it is possible to make a µPower ther-

mometer that spans a 180˚C temperature range. The LM35

temperature sensor has an output sensitivity of 10 mV/˚C,

while drawing only 50 µA of quiescent current. In order for

the LM35 to measure negative temperatures, a pull down to

a negative voltage is required.

Figure 11 shows a thermom-

eter circuit for measuring temperatures from −55˚C to

+125˚C and requiring only two 1.5V cells. End of battery life

can be extended by replacing the up converter diodes with

Schottky’s.

Regulating −V

out

It is possible to regulate the output of the LMC7660 and still

maintain µPower performance. This is done by enclosing the

LMC7660 in a loop with a LP2951. The circuit of

Figure 12

will regulate V

ror flag on pin 5 of the LP2951 sets low when the regulated

output at pin 4 drops by about 5%. The LP2951 can be shut-

down by taking pin 3 high; the LMC7660 can be shutdown by

shorting pin 7 and pin 8.

DS009136-12

FIGURE 8. Split V

DS009136-13

FIGURE 9. Positive Voltage Multiplier

DS009136-14

FIGURE 10. Combined Negative Converter and Positive Multiplier

7

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