MAX708 Application Circuit

Photocoupler

The MAX708 can also monitor the second power supply signal to provide a voltage drop warning function for the processor. This function can be used to perform some safety operations before the power supply drops to the reset state. Save the parameter to send the alarm signal or switch the backup battery. The example uses the MAX708 meter to save the current power to the E2PROM before power supply glitch or power failure, and saves multiple power backup algorithms to effectively solve the problem of power loss in the E2PROM. The circuit must select the appropriate warning. The voltage point is to ensure that the VCC voltage drops from the warning voltage to the reset voltage for the power supply. The sustain time tB of the reset voltage must be long enough. The write period of the E2PROM is about 10 20ms. Generally, the data is stable and the warning voltage is written by tB>200ms. Adjustment method When VDC is equal to the warning voltage, adjust R1 and R2 so that the voltage of PFI is 1.25V. At this time, it can detect /PFO to confirm whether the internal voltage comparator is operating. It must be noted that this comparator is a window comparator. Figure 10 is the application. Program flow chart