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CBM705/CBM706/CBM707/CBM708

OPERATION INSTRUCTION

Adding Hysteresis to the Power Fail Comparator

For increased noise immunity, hysteresis can be added to the power fail comparator.

Because the comparator circuit is noninverting, hysteresis can be added by connecting a resistor

between the PFO output and the PFI input as shown in Figure 16.

Figure 16. Adding Hysteresis to the Power Fail Comparator

When PFO is low, Resistor R3 sinks current from the summing junction at the PFI pin. When

PFO is high, Resistor R3 sources current into the PFI summing junction. This results in differing

trip levels for the comparator. Further noise immunity can be achieved by connecting a capacitor

between PFI and GND. The equations calculate the hysteresis are as follows:

×

R3

R1]