MIC2755
Micrel
MIC2755
Battery System Supervisor
Preliminary Information
General Description
The MIC2755 is composed of multiple comparators, a reset
pulse generator, and logic. It is designed for monitoring the
battery supply of portable digital systems, including PDAs
and pagers.
The MIC2755 detects three different battery states: battery
OK, low battery, and dead battery. The reset (/RST) output is
asserted for at least 700ms when a fresh battery is inserted.
The nonmaskable interrupt output (/NMI) is asserted when
the battery voltage is below the NTH threshold, indicating that
high-power system operations should not occur. If and when
battery voltage falls below the power-off threshold (PTH), the
reset output is asserted and latched, inhibiting system opera-
tion until the battery is replaced or recharged.
All three voltage thresholds are set using external resistors.
A manual reset function can be implemented by connecting
a switch directly to the power on reset/manual reset [RTH(/MR)]
input. Internal circuitry detects switch activation and gener-
ates a minimum 175ms debounced reset signal. The
MIC2755鈥檚 power supply input is separate from the detector
inputs to allow it to be powered from a down-stream voltage,
such as the output of a boost converter.
Inputs and outputs can be pulled above V
DD
(up to 7V
absolute maximum) without adverse effects or excessive
current draw.
Supply current is typically a low 2碌A. Hysteresis is included
on all voltage detectors to prevent chattering due to noise.
The MIC2755 is available in the tiny 8-lead micro-small-
outline package.
Features
鈥?Optimized for PDAs, pagers and
other hand-held devices.
鈥?Detects multiple battery states:
- battery OK
- low battery
- dead battery
鈥?Adjustable voltage thresholds
鈥?High accuracy
鹵2%
voltage thresholds
鈥?Reset generation at power-on (700ms min.)
鈥?Debounced manual reset function
鈥?Internal logic prevents chatter if battery voltage
fluctuates
鈥?Extremely low 2碌A typical supply current
鈥?I/Os can be pulled above V
DD
(7V absolute maximum)
鈥?Immune to brief power supply transients
鈥?Low cost
鈥?8-lead MSOP
Applications
鈥?/div>
鈥?/div>
鈥?/div>
鈥?/div>
鈥?/div>
鈥?/div>
PDAs
Pagers
Consumer electronics
Embedded controllers
Portable instruments
Data loggers
Ordering Information
Part Number
MIC2755BMM
Junction Temp. Range
鈥?0擄C to +85擄C
Package
8-pin MSOP
Typical Application
V
BAT
V
BAT(OK)
= 3.6V
V
BAT(low)
= 3.1V
V
BAT(dead)
= 2.9V 656k
344k
100k
576k
MIC2755
26.7k
VDD
PTH
NTH
RTH(/MR)
/POF
/NMI
/RST
GND
/NMI
/RST
Boost or Buck
Converter
IN
EN
OUT
100k 100k
碌Controller
or
碌Processor
SUPPLY
SW
RESET
400k
GND
Supervised Boost Converter and Microcontroller or Microprocessor
Micrel, Inc. 鈥?1849 Fortune Drive 鈥?San Jose, CA 95131 鈥?USA 鈥?tel + 1 (408) 944-0800 鈥?fax + 1 (408) 944-0970 鈥?http://www.micrel.com
February 2000
1
MIC2755
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