CAT823LSDI-G datasheet(10/14 Pages) CATALYST

10 / 14 page

CAT823, CAT824, CAT825

Doc. No. MD-3027 Rev. B

Characteristics subject to change without notice

APPLICATION NOTES

µP’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 1.5mA (and by the

CAT82_T/R/S/Z/Y is 800µA) 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 2µs on the power supply at VRST minimum

will not 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

maintain a valid output down to a VCC of 1.0 volts. To

sink current below 0.8V a resistor can be connected

from RESET

¯¯¯¯¯¯ to Ground (see Figure 8.)

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 100kΩ should be adequate in

most situations to maintain a low condition valid

output down to VCC equal to 0V.

Figure 8. RESET

¯¯¯¯¯¯ Valid to 0 Volts VCC

100kΩ

CAT823

VCC

GND

WDI

µC

RESET

CAT823LSDI-G Datasheet(PDF) 10 Page - Catalyst Semiconductor

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