LM3641 Datasheet, PDF (1/16 Pages) National Semiconductor (TI) – Lithium-Ion Battery Pack Protection Circuit

January 1999
LM3641
Lithium-Ion Battery Pack Protection Circuit
General Description
The LM3641 Lithium Protection Integrated Circuit resides in-
side a 3.6V Lithium-Ion battery pack consisting of a single
cell or multiple parallel cells. The IC controls the ON/OFF
state of a pair of low threshold N-channel power MOSFETs
placed in series with the battery cell(s). The purpose of this
MOSFET pair is to protect the cell(s) from inadvertent elec-
trical over-stress. The IC compares the cell voltage against
internally programmed minimum and maximum limits. Tran-
sient voltage faults of approximately 1.25 seconds are toler-
ated.
The IC also monitors the bi-directional current flow in the bat-
tery pack by measuring the voltage across a robust 4 mΩ
current sensing resistor internal to the protection IC pack-
age. The IC turns OFF the MOSFET pair whenever any fault
limit is exceeded. Momentary current surges <4 ms are tol-
erated.
The Enable pin allows external ON/OFF control of the MOS-
FET pair and resets the IC after the MOSFET pair is turned
OFF and the pack is safe to operate again.
The limits for overcharge and overdischarge voltage, as well
as independent limits for each direction of overcurrent are
factory adjusted employing EEPROM.
Features
n Automatic battery disconnect when the cell is
over-charged or over-discharged.
n Maximum cell voltage for MOSFET conduction is factory
programmable between 4.0V and 4.4V with a ±25 mV
tolerance (0˚C to +60˚C).
n Minimum cell voltage for MOSFET conduction =
0.57•V_MAX ±3.5% (0˚C to +60˚C).
n Internal 4 mΩ current sense resistor provides ±0.5A
maximum accuracy for detection of overcurrent faults.
The maximum charge and discharge current is factory
programmable between 1A and 5A. A single overcurrent
fault event opens and protects the MOSFET pair.
n Automatic detection of safe pack conditions for recovery
(MOSFET pair ON) from a fault condition (over/under
discharged or overcurrent).
n Average current drain = 1.2 µA typical.
n Optional Enable pack terminal can be used to prevent
accidental short circuit of pack and for maximizing the
shelf life of the pack (IC powers down when the pack is
not in use).
n Over-current events cause connection of an internal
50 kΩ “FET-Bypass” resistance across OFF MOSFET
pair. Loads >3–7 MΩ are required for return to
conduction mode.
n Over-charged states cause connection of a 5 kΩ
“Cell-Bypass” resistor to ensure that the cell is not
allowed to be overcharged by leakage paths.
Typical Application
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