Micrel, Inc.

MIC2774

March 16, 2015

6

Revision 2.0

Functional Diagram

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

is used to scale the input voltage to be monitored such

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.

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

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.

released (returns high), the reset output will be de-

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

unused.