PIN DESCRIPTION
Pin Name
Description
GND
Ground.
Active low output pin. RESET Output remains low while VCC is below the reset
threshold.
RESET (SP809)
Active high output pin. RESET Output remains high while VCC is below the reset
threshold.
RESET (SP810)
VCC
Supply Voltage
DETAILED DESCRIPTION
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.
Benefits of Highly Accurate Reset
Threshold
SP809/810withspecifiedvoltageas5V±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
pretrimmedthresholdsarereducingtherange
over which an undesirable reset may occur.
Reset is guaranteed to be a logic low for
VTH>V >0.9V. Once VCC exceeded the reset
threshCoCld,aninternaltimerkeepsRESETlow
for the reset timeout period; after this interval,
RESET goes high.
If a brownout condition occurs (V drops
below the reset threshold), RESET gCoCes low.
Any time VCC goes below the reset threshold,
the internal timer resets to zero, and RESET
goes low. The internal timer is activated after
V
returns above the reset threshold, and
RCECSET remains low for the reset timeout
period.
APPLICATION INFORMATION
Negative-Going VCC Transients
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.
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 VCC transient.
Interfacing to µP with Bidirectional
Reset Pins
Ensuring a Valid Reset Output Down to
VCC= 0
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.
When V falls below 0.9V, SP809 RESET
output nCoClonger 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 VCC down to
0.9V.
Date: 11/9/04
SP809/810, 3 Pin Microprocessor Supervisor Circuit
© Copyright 2004 Sipex Corporation
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