CAT823, CAT824, CAT825

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8

Application Notes

mP’s with Bidirectional Reset Pins

The RESET output can be pulled low by processors like

the 68HC11 allowing for a system reset issued by the

processor. The maximum pullup current that can be sourced

by the CAT82_L/M is 1.5 mA (and by the CAT82_T/R/S/Z/Y

is 800

mA) allowing the processor to pull the output low even

when the CAT82x is pulling it high.

Power Transients

Generally short duration negative−going transients of less

than 2

cause a reset condition. However the lower the voltage of the

transient the shorter the required time to cause a reset output.

These issues can usually be remedied by the proper location

of bypass capacitance on the circuit board.

Output Valid Conditions

The RESET output uses a push−pull output which can

current below 0.8 V a resistor can be connected from RESET

to Ground (see Figure 11.) This arrangement will maintain

a valid value on the RESET output during both power up and

down but will draw current when the RESET output is in the

high state. A resistor value of about 100 k

W should be

adequate in most situations to maintain a low condition valid

100 kW

CAT823

GND

WDI

mC

MR

RESET

RESET