MIC2779

Micrel

MIC2779

4

June 2000

Functional Description

The MIC2779 monitors the voltage of a battery and detects

when it is discharged below a programmed level. Upon being

replaced, or being recharged above a second higher pro-

grammed trip point, the output remains low (MIC2779L) or

high (MIC2779H) for a minimum of 140ms and then sends a

reset signal to a microprocessor or other downstream com-

ponent. See “Timing Diagram.”

/RST, RST Low Output

The output is a push-pull logic signal which is asserted when

the MIC2779 detects a low input voltage. The MIC2779L’s

/RST output is active-low; the MIC2779H’s RST output is

active-high.

Functional Diagram

GND

RST*

1.24V

Bandgap

Reference

Low-Voltage

Detect

High-Voltage

Detect

R

S

Q

Q

Delay

Line

LTH

HTH

MIC2779

* Pinout and polarity vary by device type.

See ordering information table.

/RST*

One Shot

Trip Points

Battery voltage is monitored by a comparator via a voltage

divider network. The divided voltage is compared to an

internal reference voltage. When the voltage at the LTH input

pin drops below the internal reference voltage, the output is

asserted. At this point, the voltage at HTH is assumed to be

below the reference voltage.

Delay

At power-on or when the battery is replaced or recharged,

and the voltage at HTH exceeds the reference voltage, the

output is deasserted after a minimum delay of 140ms.