CAT823 Datasheet, PDF (7/15 Pages) Catalyst Semiconductor – System Supervisory Voltage Reset with Watchdog and Manual Reset

CAT823, CAT824, CAT825
FUNCTIONAL DESCRIPTION
PROCESSOR RESET
The CAT823-825 detect supply voltage (V_CC)
conditions that are below the specified voltage trip
value (V_RST) and provide a reset output to maintain
correct system operation. On power-up, R¯¯E¯S¯E¯T¯ (and
RESET if available) are kept active for a minimum
delay t_RP of 140ms after the supply voltage (V_CC) rises
above V_RST to allow the power supply and processor
to stabilize. When V_CC drops below the voltage trip
value (V_RST), the reset output signals R¯¯E¯S¯E¯T¯ (and
RESET) are pulled active. R¯¯E¯S¯E¯T¯ (and RESET if
available) is specifically designed to provide the reset
input signals for processors. This provides reliable
and consistent operation as power is turned on, off or
during brownout conditions by maintaining the
processor operation in known conditions.
MANUAL RESET
The CAT823 and CAT825 each have a Manual Reset
(¯M¯R¯) input to allow for alternative control of the reset
outputs. The ¯M¯R¯ input is designed for direct con-
nection to a pushbutton (see Figure 1). The ¯M¯R¯ input
is internally pulled up by 52kΩ resistor and must be
pulled low to cause the reset outputs to go active.
Internally, this input is debounced and timed such that
R¯¯E¯S¯E¯T¯ (and RESET) signals of at least 140ms
minimum will be generated. The min 140ms t_RP delay
commences as the Manual Reset input is released
from the low level. (see Figure 2)
Figure 1. Pushbutton RESET
MR
Supply
Voltage
V_CC
CAT825
RESET
GND
RESET
Figure 2. Timing Diagram – Pushbutton RESET
MR
t_PB
t_PDLY
V_IL
RESET
RESET
V_IH
t_RP
V_OH
V_OL
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7
Characteristics subject to change without notice
Doc. No. MD-3027, Rev. D