User manual

You can see how it works in the accompanying functional diagram. There is a precision resistor diver,
voltage reference, and an output circuit with timer.
If the input voltage on the VDD pin drops below 2.64V then the RESET output will go LOW.
In our application, /RESET will be HIGH and thus the BATT LED will be ON if the battery voltage is
above 2.64V. Conveniently, this is about the “dead” point for a 3V coin cell lithium battery which
spend most of their operational life around 2.7 to 3.0V.
Making use of the same DP3T switch used for the current range selection we are able to get a very
handy “battery check” mode between the ON and OFF modes that switches in U3 to light the LED.