MIC2755_06 Datasheet, PDF (1/10 Pages) Micrel Semiconductor – Battery System Supervisor

MIC2755
MIC2755
Micrel, Inc.
Battery System Supervisor
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
operation 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
generates a minimum 175ms debounced reset signal. The
MIC2755’s 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 2µA. Hysteresis is included
on all voltage detectors to prevent chattering due to noise.
The MIC2755 is available in the tiny 8-pin micro-small-outline
package.
Features
• Optimized for PDAs, pagers and
other hand-held devices.
• Detects multiple battery states:
- battery OK
- low battery
- dead battery
• Adjustable voltage thresholds
• High accuracy ±2% voltage thresholds
• Reset generation at power-on (700ms min.)
• Debounced manual reset function
• Internal logic prevents chatter if battery voltage
fluctuates
• Extremely low 2µA typical supply current
• I/Os can be pulled above V_DD (7V absolute maximum)
• Immune to brief power supply transients
• Low cost
• 8-pin MSOP
Typical Application
V_BAT
V_BAT(OK) = 3.6V
V_BAT(low) = 3.1V
V_BAT(dead) = 2.9V
656k
576k
344k 26.7k
SW
RESET
400k
100k
MIC2755
VDD
/POF
PTH
/NMI
NTH
/RST
RTH(/MR) GND
Boost or Buck
Converter
IN OUT
EN
100k 100k
µController or
µProcessor
SUPPLY
/NMI
/RST
GND
Supervised Boost Converter and Microcontroller or Microprocessor
Micrel, Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 [phone] • fax + 1 [phone] • http://www.micrel.com
January 2006
1
MIC2755