FMFFM1233AC Datasheet, PDF (5/7 Pages) Fairchild Semiconductor – 3-Pin uC Supervisor Circuit

General Description
The FM1233A features a highly accurate voltage reference to
which V_CC is compared. Once V_CC is below the specified thresh-
old, it will drive the RESET line and continue to hold it low until
V_CC returns above the threshold and the time for the RESET
pulse duration has expired. The FM1233A is immune to short
negative going transients on the V_CC line. The placement of a
0.1µF bypass capacitor as close as possible to the V_CC pin pro-
vides additional transient immunity.
For a V_CC value below 1.0V, the FM1233A does not sink very
much current on the RESET pin. This is not a problem in most
systems since common devices are not functional in this range.
If it is desired for the FM1233A reset to be functional below this
range, use a 100KΩ pull-down resistor between RESET and
V_SS.
Bi-Directional Reset
The FM1233A permits a pushbutton (or a signal) to initiate a
reset externally. Once this external reset is detected on the
reset pin, FM1233 also actively asserts the reset signal to main-
tain the Reset Timeout period when the external reset is not
present .
FM1233 internally debounces glitches seen during a typical
push button closure. For proper operation, the external switch
should be paralleled by an external capacitor of 100pF to
0.01µF.
Connecting an External Reset to the FM1233A
VCC
3
FM1233
Controller
GND
1
2
RESET
PUSH
BUTTON
100pF
FM1233A Rev. E
5
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