MIC2776_05 Datasheet, PDF (5/8 Pages) Micrel Semiconductor – Micro-Power Low Voltage Supervisor

MIC2776
Functional Diagram
V_DD
I_PU
/MR
IN
GND
V_REF
Micrel, Inc.
RQ
Delay ^{One Shot}
S
/Q
/RST*
RST*
MIC2776
* Pinout and polarity vary by device type.
See ordering information table.
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 chat-
tering 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. As-
suming 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 con-
nected 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.
November 2005
5
MIC2776