5

Date: 5/02/06 Rev B

SP809/810, 3 Pin Microprocessor Supervisor Circuit

© Copyright 2006 Sipex Corporation

PIN DESCRIPTION

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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

V

threshold, an internal timer keeps RESET low

for the reset timeout period; after this interval,

RESET goes high.

If a brownout condition occurs (V

below the reset threshold), RESET goes low.

Any time V

the internal timer resets to zero, and RESET

goes low. The internal timer is activated after

V

RESET remains low for the reset timeout

period.

DETAILED DESCRIPTION

Benefits of Highly Accurate Reset

Threshold

SP809/810 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 below the minimum specified operating

voltage range of the system ICs. The

pretrimmed thresholds are reducing the range

over which an undesirable reset may occur.

APPLICATION INFORMATION

Negative-Going V

In addition to issuing a reset to the µP during

power-up, power-down, and brownout condi-

tions, SP809 series are relatively resistant to

short-duration negative-going V

Ensuring a Valid Reset Output Down to

VCC= 0

When V

output no longer sinks current; it becomes

an open circuit. In this case, high-imped-

ance CMOS logic inputs connecting to

RESET can drift to undetermined voltages.

Therefore, SP809/810 with CMOS is

perfect for most applications of V

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

Reset Pins

The RESET output on the SP809N is open

drain, this device interfaces easily with µPs

that have bidirectional reset pins. Connect-

ing 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.