MIC2779_06 Datasheet, PDF (4/6 Pages) Micrel Semiconductor – Voltage Monitor with Adjustable Hysteresis

MIC2779
Micrel, Inc.
Functional Diagram
V_{B A T T}
V_DD
Low-Voltage
Detect
LTH
V_LO
HTH
V_HI
High-Voltage
Detect
Delay
Line
One Shot
RQ
SQ
/RST*
RST*
1.24V
Bandgap
Reference
GND
MIC2779
* Pinout and polarity vary by device type.
See ordering information table.
Functional Description
The MIC2779 monitors the voltage of a battery and detects
when it is discharged below a programmed level. Upon be-
ing replaced, or being recharged above a second higher
programmed 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
component. 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.
Trip Points
Battery voltage is monitored by a comparator via a voltage
divider network. The divided voltage is compared to an in-
ternal 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.
MIC2779
4
January 2006