MIC2774 Datasheet, PDF (5/8 Pages) Micrel Semiconductor – Dual Micro-Power Low Voltage Supervisor Advance Information

MIC2774
Functional Diagram
V_DD
IN
V_DD
I_PU
V_REF
V_REF
/MR
GND
* Pinout and polarity vary by device type.
See ordering information table.
RQ
Delay
Line
One Shot
S /Q
/RST*
RST*
MIC2774
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. The comparator on the IN pin is relatively immune to
very brief negative-going transients.
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 Output
Typically, the MIC2774 is used to monitor the power supplies
of intelligent circuits such as microcontrollers and micropro-
cessors. By connecting the appropriate reset output of a
MIC2774 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 output is asserted any time /MR is asserted or if V_IN
or V_DD drops below the corresponding threshold voltage. The
reset output remains asserted for t_RST(min) after V_IN and/or
V_DD subsequently return above the threshold boundaries
and/or /MR is released. A reset pulse is also generated at
power-on. Hysteresis is included in the comparators to pre-
vent chattering of the output 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 MIC2774’s automatic
supervisory functions. Driving the /MR input to a logic low
causes an immediate and unconditional reset to occur.
Assuming V_IN and V_DD are 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. Switch de-bouncing is performed
internally; the switch may be connected directly between /MR
and GND. /MR is internally pulled-up to V_DD and may be left
open if unused.
September 29, 2000
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MIC2774