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SS809/810G

9/20/2006 Rev.3.01

DETAILED DESCRIPTIONS OF TECHNICAL TERMS

RESET OUTPUT

The µP will be activated at a valid reset state. These

µP supervisory circuits assert reset to prevent code

execution errors during power-up, power-down, or

brownout conditions.

RESET is guaranteed to be a logic low for

threshold, an internal timer keeps RESET low for

the reset timeout period; after this interval, RESET

goes high.

goes below the reset threshold, the internal timer

resets to zero, and RESET goes low. The internal

threshold, and RESET remains low for the reset

timeout period.

BENEFITS

OF

HIGHLY

ACCURATE

RESET

THRESHOLD

The SS809G and SS810G with specified voltage as 5V

±

10% or 3V

±10% are ideal for systems using a 5V±5%

or 3V

±5% power supply. The reset is guaranteed to

assert after the power supply falls out of regulation,

but before the power drops below the minimum

specified operating voltage range of the system ICs.

The pre-trimmed thresholds reduce the range over

which an undesirable reset may occur.

APPLICATION INFORMATION

NEGATIVE-GOING VCC TRANSIENTS

In addition to issuing a reset to the

µP during

power-up, power-down, and brownout conditions, the

SS809G series are relatively resistant to short-duration

negative-going VCC transients.

ENSURING A VALID RESET OUTPUT DOWN TO

VCC=0

When VCC falls below 0.9V, the SS809G RESET

output no longer sinks current; it becomes an open

circuit. In this case, high-impedance CMOS logic

inputs

connected

to

RESET

can

drift

to

undetermined voltages. Therefore, the SS809G/810G

are perfect for most CMOS applications down to VCC

of 0.9V. However in applications where RESET

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

to RESET causes any leakage currents to flow to

ground, holding RESET low.

INTERFACING TO A MICROPROCESSOR WITH

BIDIRECTIONAL RESET PINS

The RESET output on the SS809N is open drain,

and 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-up

resistor allows either device to assert reset.