November 2005

5

MIC2776

MIC2776

Micrel, Inc.

Functional Description

IN, Under-Voltage Detector Input

The voltage present at the IN pin is compared to the internal

300mV reference voltage. A reset is triggered if and when

desired trip-point. Hysteresis is employed to prevent chat-

tering due to noise.

RST, /RST Reset Output

Typically, the MIC2776 is used to monitor the power supply

of intelligent circuits such as microcontrollers and micropro-

cessors. By connecting the reset output of a MIC2776 to the

reset input of a µC or µP, the processor will be properly reset

at power-on and during power-down and brown-out condi-

tions. In addition, asserting /MR, the manual reset input, will

activate the reset function.

Functional Diagram

R

S

Q

/Q

/MR

IN

MIC2776

* Pinout and polarity vary by device type.

See ordering information table.

/RST*

RST*

GND

Delay

One Shot

The reset outputs are asserted any time /MR is asserted or

above the threshold boundary and /MR is released. A reset

pulse is also generated at power-on.

/MR, Manual Reset Input

The ability to initiate a reset via external logic or a manual

switch is provided in addition to the MIC2776’s automatic

supervisory functions. Driving the /MR input to a logic low

causes an immediate and unconditional reset to occur. As-

later. /MR may be driven by a logic signal, or mechanical

switch. Typically, a momentary push-button switch is con-

nected such that /MR is shorted to ground when the switch

contactsclose.Theswitchmaybeconnecteddirectlybetween

/MR and GND. /MR has an internal 100nA pull-up current to