Supervisory Circuits

A supervisory circuit is an electronic circuit used to monitor one or more system parameters (such as power supplies and microprocessors). These parameters must be kept within a specific range, and appropriate measures will be taken when the parameters exceed the range, resulting in an unacceptable or dangerous situation.

Supervisory circuits are known by various names, including battery monitors, power supply monitors, supply supervisory circuits, and reset circuits.

The supervisory circuit can be used in many different applications, but there are two primary functions that a supervisor provides:

1. During the power up sequence, the device holds a microcontroller in reset until the system power has come up to the correct level and stabilized (the POR function)。

2. reset the controller immediately if the power drops below a nominal value either at power down or during a 'brown-out' condition. 

Some supervisor devices also provide things like low battery warning, watchdog timer, and other more elaborate functions beyond this application note's scope.