CAT705 Datasheet, PDF (10/14 Pages) Catalyst Semiconductor – μP Supervisory Circuits

CAT705, CAT706, CAT813
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 CAT705 & CAT706 1.5mA (and by
the CAT706 T/R/S is 800µA) allowing the processor to
pull the output low even when the CAT70x 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 1.0V.
MR
WDO
V_CC
GND
CAT705
CAT706
CAT813
RESET/RESET
WDI
PFI
PFO
µC
RESET/RESET
100kΩ
Figure 8. R¯¯E¯S¯E¯T¯ Valid for V_CC < 1.0V
Push Switch
UNREGULATED DC
5V
MR
WDO
V_CC
GND
CAT705
CAT706
CAT813
RESET/RESET
WDI
PFI
PFO
VCC
µC
NMI
RESET/RESET
I/O LINE
INTERRUPT
Figure 9. Typical Operating Circuit
Doc. No. MD-3030 Rev. A
10
© Catalyst Semiconductor, Inc.
Characteristics subject to change without notice