MIC2775_15 Datasheet, PDF (6/9 Pages) Micrel Semiconductor – Micro-Power Voltage Supervisor

Micrel, Inc.
Functional Diagram
MIC2775
Functional Description
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 Outputs
Typically, the MIC2775 is used to monitor the power
supply of intelligent circuits such as microcontrollers and
microprocessors. By connecting the appropriate reset
output of an MIC2775 to the reset input of a µC or µP, the
processor will be properly reset at power-on, 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 contact close. The switch may be
connected directly between /MR and GND. /MR has an
internal 100nA pull-up current to VDD and may be left
open if unused.
March 23, 2015
6
Revision 4.0