LMC7660

SNOSBZ9C – APRIL 1997 – REVISED APRIL 2013

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THERMOMETER SPANS 180°C

Using the combined negative and positive multiplier of Figure 20 with an LM35 it is possible to make a

μPower

thermometer 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 20 shows a thermometer 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

−VOUT

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 21 will regulate Vout to −5V for IL = 10 mA,

and Vin = 6V. For Vin > 7V, the output stays in regulation up to IL = 25 mA. The error flag on pin 5 of the LP2951

sets low when the regulated output at pin 4 drops by about 5%. The LP2951 can be shutdown by taking pin 3

high; the LMC7660 can be shutdown by shorting pin 7 and pin 8.

The LP2951 can be reconfigured to an adjustable type regulator, which means the LMC7660 can give a

regulated output from

−2.0V to −10V dependent on the resistor ratios R1 and R2, as shown in Figure 22, Vref =

1.235V:

(4)

*For lower voltage operation, use Schottky rectifiers

Figure 20.

μPower Thermometer Spans 180°C, and Pulls Only 150 μA

Figure 21. Regulated

−5V with 200 μA Standby Current

10

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