MIC2774_15 Datasheet, PDF (6/11 Pages) Micrel Semiconductor – Dual Micro-Power Low Voltage Supervisor

Micrel, Inc.
Functional Diagram
MIC2774
Note: *Pinout and polarity vary by device type. See the Ordering Information table.
Functional Description
IN, Undervoltage 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 immunue to very
brief negative-going transients.
VDD Input
The VDD pin is both the power supply terminal and a
monitored 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. Hysteresis is employed to prevent chattering due to
noise. The comparator on the VDD 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 microprocessors. By connecting the appropriate
reset output of an MIC2774 to the reset input of a µC or
µP, the processor will be properly reset at power-on,
power-down, and during 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 of
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
isincluded in the comparators to prevent 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.
March 16, 2015
6
Revision 2.0