MIC2775 Datasheet, PDF (5/7 Pages) Micrel Semiconductor – Micro-Power Voltage Supervisor Advance Information

MIC2775
Functional Diagram
V_DD
/MR
V_DD
V_REF
I_PU
GND
Micrel
RQ
/RST
Delay
Line
One Shot
S /Q
MIC2775
RST
Functional Description
V_DD Input
The V_DD pin is both the power supply terminal and a moni-
tored input voltage. The voltage at this pin is continually
compared against the internal reference. The trip-point at
which a reset occurs is factory programmed. A reset is
triggered if and when V_DD falls below the trip-point. Hyster-
esis is employed to prevent chattering due to noise. The
comparator on the V_DD input is relatively immune to very brief
negative-going transients.
RST, /RST Reset Outputs
Typically, the MIC2775 is used to monitor the power supply
of intelligent circuits such as microcontrollers and micropro-
cessors. By connecting the appropriate reset output of a
MIC2775 to the reset input of a µC or µP, the processor will
be properly reset at power-on and during power-down and
brown-out conditions. In addition, asserting /MR, the manual
reset input, will activate the reset function.
The reset outputs are asserted any time /MR is asserted or if
V_DD drops below the threshold voltage. The reset outputs
remain asserted for t_RST(min) after V_DD subsequently returns
above the threshold boundary and/or /MR is released. A reset
pulse is also generated at power-on. Hysteresis is included in
the comparator to prevent chattering of the outputs due to
noise.
/MR, Manual Reset Input
The ability to initiate a reset via external logic or a manual
switch is provided in addition to the MIC2775’s automatic
supervisory functions. Driving the /MR input to a logic low
causes an immediate and unconditional reset to occur.
Assuming V_DD is within tolerance when /MR is released
(returns high), the reset outputs will be de-asserted no less
than t_RST later. /MR may be driven by a logic signal or
mechanical switch. Typically, a momentary push-button switch
is connected such that /MR is shorted to ground when the
switch contacts close. The switch may be connected directly
between /MR and GND. /MR has an internal 100nA pull-up
current to V_DD and may be left open if unused.
September 29, 2000
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MIC2775