Micrel, Inc.

MIC2775

March 23, 2015

6

Revision 4.0

Functional Diagram

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.

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

outputs

remain

asserted

for

after

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.

(returns high), the reset outputs will be de-asserted no

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.