January 2007
rev 0.2
PCS809/PCS810
Detailed Description
RESET OUTPUT
returns above the reset threshold, and RESET remains
low for the reset timeout period.
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
RESET is guaranteed to be
a
logic low for
PCS809/810 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 out of regulation, but before power
drops below the minimum specified operating voltage
range of the system ICs. The pre-trimmed thresholds are
reducing the range over which an undesirable reset may
occur.
VTH>VCC>0.9V. Once VCC exceeds the reset threshold,
an internal timer keeps RESET low for the reset timeout
period; after this interval, RESET goes high.
If a brownout condition occurs (VCC drops below the reset
threshold), RESET goes 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 VCC
Application Information
NEGATIVE-GOING VCC TRANSIENTS
VCC below 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.
In addition to issuing a reset to the µP during power-up,
power-down, and brownout conditions, PCS809 series are
relatively resistant to short-duration negative-going VCC
transient.
ENSURING
VCC=0
A
VALID RESET OUTPUT DOWN TO
INTERFACING TO µP WITH BIDIRECTIONAL RESET
PINS
When VCC falls below 0.9V, PCS809 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,
PCS809/810 with CMOS is perfect for most applications of
The RESET output on the PCS809 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-up resistor allows either device to assert reset.
3-Pin µP Voltage Supervisor
3 of 8
Notice: The information in this document is subject to change without notice.