AN834 Datasheet, PDF (2/3 Pages) Silicon Laboratories – ALKALINE BATTERY LOW-VOLTAGE INDICATOR

AN834

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Figure 2. Voltage Monitoring Circuit
This circuit takes advantage of some new voltage comparators from Silicon Labs. The TSM9118 has an internal
1.25 V reference and an open drain output while drawing an astoundingly low 0.7 µA. That circuit is configured as
a classic voltage monitoring circuit, which changes state at a 2.5 V battery voltage. A second TSM9119 part is
wired as a 0.5 Hz oscillator which is configured to produce short 20 ms output pulses every 2 seconds. The
TSM9119 is a conventional comparator with a push-pull output, which also draws a very low current. Using the two
low power parts, the total standby current of the circuit is kept at a low 3 µA. When the LED starts flashing, the
average current will increase to about 50 µA. This is still low enough that the circuit should continue flashing for
some time, giving the user time to notice the warning and replace the batteries. For additional information, contact
Silicon Labs.
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Rev. 1.0