MIC2778
Micrel
MIC2778
Voltage Monitor with Adjustable Hysteresis
Preliminary Information
General Description
The MIC2778 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) 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
not requiring built-in delay, see MIC833.
The IC’s power supply input is separate from the detector
inputs, allowing the MIC2778 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 MIC2778 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 not requiring built-in delay, see MIC833
• Immune to brief power supply transients
• 5-lead SOT-23 package
Applications
•
•
•
•
•
•
PDAs
Pagers
Cordless phones
Consumer electronics
Embedded controllers
Personal electronics
Ordering Information
Part Number
MIC2778-2BM5
MIC2778-1BM5
Marking
UFB
UFA
Accuracy
2%
1%
Temperature Range
–40°C to +85°C
–40°C to +85°C
Package
SOT-23-5
SOT-23-5
Typical Application
MIC5207-3.0BM5
Li-Ion
Cell
MIC2778
VDD
LTH
56k
1%
340k
1%
HTH
GND
RST
IN
100k
EN
OUT
BYP
GND
470pF
V
OUT
3.0V
4.7µF
604k
1%
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
October 1999
1
MIC2778
MICREL [ MICREL SEMICONDUCTOR ]
