CAT823 Datasheet, PDF (10/14 Pages) Catalyst Semiconductor – System Supervisory Voltage Reset with Watchdog and Manual Reset

CAT823, CAT824, CAT825
APPLICATION NOTES
µP’s with Bidirectional Reset Pins
The R¯¯E¯S¯E¯T¯ 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 1.5mA (and by the
CAT82_T/R/S/Z/Y is 800µA) 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 2µs 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 R¯¯E¯S¯E¯T¯ 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 0.8V a resistor can be connected
from R¯¯E¯S¯E¯T¯ to Ground (see Figure 8.) This
arrangement will maintain a valid value on the R¯¯E¯S¯E¯T¯
output during both power up and down but will draw
current when the R¯¯E¯S¯E¯T¯ output is in the high state. A
resistor value of about 100kΩ should be adequate in
most situations to maintain a low condition valid
output down to V_CC equal to 0V.
Figure 8. R¯¯E¯S¯E¯T¯ Valid to 0 Volts V_CC
WDI
CAT823
V_CC
MR
GND
RESET
100kΩ
µC
RESET
Doc. No. MD-3027 Rev. A
10
© Catalyst Semiconductor, Inc.
Characteristics subject to change without notice