Datasheet

LMC7660
SNOSBZ9C –APRIL 1997–REVISED APRIL 2013 www.ti.com
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 −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 21 will regulate V
out
to −5V for I
L
= 10 mA,
and V
in
= 6V. For V
in
> 7V, the output stays in regulation up to I
L
= 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, V
ref
=
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
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