CAT823, CAT824, CAT825
http://onsemi.com
8
Application Notes
mP’s with Bidirectional Reset Pins
The RESET output can be pulled low by processors like
the 68HC11 allowing for a system reset issued by the
processor. The maximum pullup current that can be sourced
by the CAT82_L/M is 1.5 mA (and by the CAT82_T/R/S/Z/Y
is 800 mA) allowing the processor to pull the output low even
when the CAT82x is pulling it high.
Power Transients
Generally short duration negative−going transients of less
than 2 ms on the power supply at V
RST
minimum will not
cause a reset condition. However the lower the voltage of the
transient the shorter the required time to cause a reset output.
These issues can usually be remedied by the proper location
of bypass capacitance on the circuit board.
Output Valid Conditions
The RESET
output uses a push−pull output which can
maintain a valid output down to a V
CC
of 1.0 volts. To sink
current below 0.8 V a resistor can be connected from RESET
to Ground (see Figure 11.) This arrangement will maintain
a valid value on the RESET
output during both power up and
down but will draw current when the RESET
output is in the
high state. A resistor value of about 100 kW should be
adequate in most situations to maintain a low condition valid
output down to V
CC
equal to 0 V.
100 kW
CAT823
GND
WDI
mC
Figure 11. RESET Valid to 0 Volts V
CC
V
CC
MR
RESET
RESET
