Technical Data

3-Pin Microprocessor Reset Circuits

Data Sheet N1589 Rev. -

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SSR809N

SSR809P/SSR810P

Application Information

NEGATIVE-GOING VCC TRANSIENTS

In addition to issuing a reset to the μP during power-up, power-down, and brownout conditions, SSR809P

series are relatively resistant to short-duration negative-going VCC transient.

ENSURING A VALID RESET OUTPUT DOWN TO VCC=0

When VCC falls below 0.9V, SSR809P RESET

———————

output no longer sinks current; it becomes an open circuit. In

this case, high-impedance CMOS logic inputs connecting to RESET

———————

can drift to undetermined voltages.

Therefore, SSR809P/SSR810P with CMOS is perfect for most applications of VCC below 0.9V. However in

applications where RESET

———————

must be valid down to 0V, adding pull-down resistor to RESET

———————

causes any

leakage currents to flow to ground, holding RESET

———————

low.

INTERFACING TO μP WITH BIDIRECTIONAL RESET PINS

The RESET output on the SSR809N is open drain, this device interfaces easily with μPs that have

bidirectional reset pins. Connecting the μP supervisor’s RESET

———————

output directly to the microcontroller’s RESET

———————

pin with a single pull-resistor allows either device to assert reset.

Application Circuit