MIC2779
Micrel
MIC2779
Voltage Monitor with Adjustable Hysteresis
Preliminary Information
General Description
The MIC2779 is a voltage monitor—uniquely designed to
detect two separate voltage thresholds—combined with a
delay generator and logic. It is designed for monitoring the
battery supply of portable digital systems, particularly PDAs,
pagers, and cellular telephones.
High- and low-voltage thresholds can be adjusted indepen-
dently, allowing for wide hysteresis. Voltage detection thresh-
olds are accurate to 2%.
If the battery voltage falls below the low-voltage threshold, the
output /RST or RST is asserted and latched, preventing
system operation until the battery is replaced or recharged.
Internal logic prevents the output from chattering due to
battery recovery or load removal. The output is asserted for
140ms (minimum) when a fresh battery is inserted. For
applications requiring open-drain output, see MIC2778/
MIC833.
The IC’s power supply input is separate from the detector
inputs, allowing the MIC2779 to be powered from a down-
stream supply, such a boost converter. Supply current is
extremely low (1µA, typical), making it ideal for portable
applications.
A high-precision 1% grade is available. The MIC2779 is
supplied in Micrel’s IttyBitty™ 5-lead SOT-23-5 package.
Features
• Optimized for PDAs, cellular telephones, pagers,
and other battery-powered devices
• Independently adjustable high- and
low-voltage thresholds
• Internal logic prevents battery-voltage-fluctuation chatter
• High
±2%
voltage threshold accuracy; 1% available
• Built in 140ms (minimum) delay deglitches output
• Extremely low 1µA typical supply current
• For applications requiring open-drain output, see
MIC2778/MIC833
• Immune to brief power supply transients
• 5-lead SOT-23 package
Applications
•
•
•
•
•
•
PDAs
Pagers
Cordless phones
Consumer electronics
Embedded controllers
Personal electronics
Typical Application
MIC5207-3.0BM5
IN
Li-Ion
Cell
604k
1%
56k
1%
340k
1%
MIC2779L
VDD
LTH
HTH
GND
/RST
EN
OUT
BYP
GND
470pF
V
OUT
3.0V
4.7µF
V
BAT(hi)
= 3.6V
V
BAT(lo)
= 3.1V
Cellular Telephone Battery Monitor
IttyBitty™ is a trademark of Micrel, Inc.
Micrel, Inc. • 1849 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 944-0970 • http://www.micrel.com
June 2000
1
MIC2779
MICREL [ MICREL SEMICONDUCTOR ]
