MIC2778
Micrel
Functional Diagram
V
BATT
Low-Voltage
Detect
LTH
R Q
HTH
V
HI
High-Voltage
Detect
Delay
Line
S Q
RST
V
LO
1.24V
Bandgap
Reference
MIC2778
GND
Functional Description
The MIC2778 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 for a minimum of
140ms and then sends a reset signal to a microprocessor or
other downstream component.
Voltage Low Output
The voltage-low output (RST) is an active-low, open-drain
output which sinks current when the MIC2778 detects a low
input voltage.
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
pulls low. 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 goes high after a minimum delay of 140ms.
MIC2778
4
October 1999
MICREL [ MICREL SEMICONDUCTOR ]
