LM3641| Datasheet

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LM3641 Lithium-Ion Battery Pack Protection Circuit

January 1999

LM3641 Lithium-Ion Battery Pack Protection Circuit
General Description
The LM3641 Lithium Protection Integrated Circuit resides inside 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 electrical over-stress. The IC compares the cell voltage against internally programmed minimum and maximum limits. Transient voltage faults of approximately 1.25 seconds are tolerated. The IC also monitors the bi-directional current flow in the battery pack by measuring the voltage across a robust 4 m current sensing resistor internal to the protection IC package. The IC turns OFF the MOSFET pair whenever any fault limit is exceeded. Momentary current surges < 4 ms are tolerated. The Enable pin allows external ON/OFF control of the MOSFET 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 VMAX 3.5% (0 C to +60 C). n Internal 4 m 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 uA 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 k "FET-Bypass" resistance across OFF MOSFET pair.
Loads > 3 7 M are required for return to conduction mode. n Over-charged states cause connection of a 5 k "Cell-Bypass" resistor to ensure that the cell is not allowed to be overcharged by leakage paths.

Typical Application

DS012931-1

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1999 National Semiconductor Corporation

DS012931

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