Supervisory products are used for monitoring power supplies to a microcontroller and ensuring software is running correctly. The less integrated devices, such as the ADM809 are also used as battery monitors. Both the cost and risk of system design is reduced significantly. When a supervisory device determines the correct supplies are no longer available to the microcontroller a gate can be opened preventing the CE input to memory being asserted. This prevents a potentially out of tolerance microcontroller addressing memory.
Many applications use a back-up battery to replace the main power source in the event of failure.
The transistor necessary to make this switch-over is offered on several of the Analog Devices supervisory parts. These are the common packages used by Analog Devices for supervisory functions. The comparators used in a supervisory circuit need to be immune to the glitches normally seen on a supply rail. Resets should not be inadvertently caused by noise sources such as neon lights, electric motors, digital circuitry, etc. Through several years of shipping supervisory circuits Analog Devices have built up a body of knowledge on optimal comparator design to eliminate unwanted reset triggering.