Product Description

Normal charging of Li-Ion packs requires Constant Voltage

Constant Current (CVCC) chargers that terminate charging

at a voltage value just below the maximum protection volt-

age (V

of compliance charger operation should the protection IC ter-

minate charging.

OVERCHARGE PROTECTION

The IC protects the cell(s) against overcharge. Normally, the

cell voltage is sampled once a second. Four consecutive

samples of V

OFF. The transient response for overvoltage requires one

sample at the t

OVERVOLTAGE

periods (0.25s typical). The first overcharge

event is asynchronous to the 1 second sampling so the delay

between the actual instance of overcharge and the first

sample can result anywhere in the range of zero to t

The requirement for 4 consecutive samples of V

filters noise from the cell due to transient currents. Should

the cell voltage exceed V

the MOSFETs will turn off on the first sample reading. This

provides an extra measure of safety. The return to conduc-

tion mode requires that a load be applied to the pack or

V

will reset the GATE high, but if V

go low again after 1.75 seconds. Whenever an overcharge

disconnect has occurred, a cell bypass resistor (

≈5kΩ)is

switched across the V

to near V

discharged even though some component of R1’s current

will still flow in the cell, if a charger is applied. The cell by-

pass resistor is removed when V

ACTIVE RECTIFICATION

Overcharged cells can be discharged by the application of a

load to the pack. Active Rectification is the biasing of the

power MOSFETs GATE so that the V

charge currents. The MOSFETs turn OFF for charge cur-

rents. The Active Rectification amplifier assures uninter-

rupted conduction for discharge currents only. The Full pin’s

output impedance is

≈80 kΩ when active high (V

V

Full pin can optionally supply a small FET current necessary

to stabilize the Active Rectification loop by maintaining at

least (V

overcharge signal could be used in applications where the

charger is logically disabled by the protection circuit, a

change time-out circuit is initiated or whenever an over-

charge signal is otherwise desired. The Full signal will go low

(TRI-STATE with an external resistor pulldown) and cell by-

pass turns off if a cell decays to V

OVERDISCHARGE PROTECTION

The cell(s) are also protected against overdischarge. Four

consecutive 1 Hz samples of V

MOSFET pair turning OFF. Cells that have discharged below

V

MIN

due to long periods of self-discharge can still be

charged. Return to conduction mode for overdischarged

packs automatically occurs if a charger is applied to the

pack. Also a L→H signal on the Enable pin will reset the

GATE high, however if V

OFF again in 4 seconds.

OVERCURRENT PROTECTION

The battery current is monitored continuously by measuring

the voltage across the internal sense resistor. If the terminal

current exceeds I

mode for longer than t

connects. Similarly, if the terminal current exceeds I

MAX-DIS

(programmable) in the discharge mode for longer than

t

conduction mode requires either 1) a momentary detach-

ment of the pack so the Enable pin can be cycled low, then

high or 2) a direct low to high signal to the Enable pin con-

trolled from logic.

ENABLE PIN

The pack can be protected from accidental short circuits

should the Enable pin be made available as a third battery

pack terminal. This third pack terminal is tied to the pack’s

positive terminal through a connection on either a valid

charger or load. Shorting the high impedance Enable pin to

the pack’s positive terminal enables all functions of the pro-

tection circuit. The Enable pin disables the MOSFET pair

whenever this pin is floating, such as when the battery pack

is detached from a valid load or charger. Floating the Enable

pin also forces the protection circuit into FET’s OFF mode to

maximize the shelf life of the battery pack. When the Enable

pin is used to recover from overcharge, overdischarge or

overcurrent events, the voltage measurement system

memory is cleared of previous results. If the MOSFET by-

pass resistor is active, and the Enable goes low, the bypass

resistor turns OFF. A series resistor of 470 k

Ω to1MΩ be-

tween the Enablel terminal of the pack and the Enable pin of

the IC, protects the IC from ESD events at the pack’s termi-

nals.

SLEEPMODE

Sleepmode is a reduced current state that occurs when the

Enable pin is floating or low. The FETs are turned OFF.

Sleepmode minimizes the artificial self-discharge of the pack

when the pack is not in use.

INVALID CHARGER

Assume a charger that exceeds the V

applied to the pack. The power MOSFETs will eventually turn

OFF due to overcharge if I

due to overcurrent if the invalid charger’s current exceeds

I

larity reversed, then the MOSFETs would eventually turn

OFF due to either overdischarge or overcurrent depending

on the magnitude of the charger’s available current. In either

case, the voltage on the V− pin will be driven by the open cir-

cuit voltage of the charger. The V− pin is clamped by internal

diodes to V

(see the typical curve “Pin Current vs. Pin Voltage”) with R1

= 100k, the pin current will not exceed the maximum recom-

invalid charger voltages can be tolerated when using higher

values for R1. Proper LCCE operation is not limited, even by

values for R1 in excess of 1 M

Ω.

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