MIC2774 datasheet(6/18 Pages) MICROCHIP

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MIC2774

DS20006527A-page 6



2022 Microchip Technology Inc.

3.0

FUNCTIONAL DESCRIPTION

3.1

IN, Undervoltage Detector Input

The voltage present at the IN pin is compared to the

internal 300 mV reference voltage. A reset is triggered

if and when VIN falls below VREF. Typically, a resistor

divider is used to scale the input voltage to be

monitored such that VIN will fall below VREF 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.

3.2

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

VDD 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.

3.3

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,

or if VIN or VDD drops below the corresponding

threshold voltage. The reset output remains asserted

for tRST(min) after VIN and/or VDD 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 prevent

chattering of the output due to noise.

3.4

/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 VIN and VDD are within

tolerance when /MR is released (returns high), the

reset output will be de-asserted no less than tRST 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 VDD and may be left open if unused.

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