MIC2776 Datasheet, PDF (5/8 Pages) Micrel Semiconductor – Micro-Power Low Voltage Supervisor

MIC2776
Functional Diagram
V_DD
I_PU
/MR
IN
GND
V_REF
RQ
One Shot
Delay
S /Q
/RST*
RST*
MIC2776
* Pinout and polarity vary by device type.
See ordering information table.
Micrel
Functional Description
IN, Under-Voltage Detector Input
The voltage present at the IN pin is compared to the internal
300mV reference voltage. A reset is triggered if and when V_IN
falls below V_REF. Typically, a resistor divider is used to scale
the input voltage to be monitored such that V_IN will fall below
V_REF as the voltage being monitored falls below the desired
trip-point. Hysteresis is employed to prevent chattering due to
noise.
RST, /RST Reset Output
Typically, the MIC2776 is used to monitor the power supply
of intelligent circuits such as microcontrollers and micropro-
cessors. By connecting the reset output of a MIC2776 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 condi-
tions. 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_IN drops below the threshold voltage. The reset outputs
remain asserted for t_RST(min) after V_IN subsequently returns
above the threshold boundary and /MR is released. A reset
pulse is also generated at power-on.
/MR, Manual Reset Input
The ability to initiate a reset via external logic or a manual
switch is provided in addition to the MIC2776’s automatic
supervisory functions. Driving the /MR input to a logic low
causes an immediate and unconditional reset to occur.
Assuming V_IN is within tolerance when /MR is released
(returns high), the reset output 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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MIC2776