UCC39571, UCC39572, UCC39573, UCC39574

SLUS236B – JANUARY 1999 – REVISED SEPTEMBER 2002

THREE OR FOURCELL LITHIUMION

PROTECTOR CIRCUIT

1

www.ti.com

FEATURES

Overcharge Mode

Controller

DESCRIPTION

The UCC3957 is a BiCMOS three- or four-cell

lithium-ion battery pack protector designed to

operate with external P-channel MOSFETs.

Utilizing external P-channel MOSFETs provides

the benefits of no loss-of-system ground in an

overdischarge state, and protects the IC as well as

battery cells from damage during an overcharge

state. An internal state machine runs continuously

to protect each lithium-ion cell from overcharge

and overdischarge. A separate overcurrent-

protection block protects the battery pack from

excessive discharge currents.

If any cell voltage exceeds the overvoltage

threshold, the appropriate external P-channel

MOSFET is turned off, preventing further charge

current. An external N-channel MOSFET is

required to level shift to this high-side P-channel

MOSFET. Discharge current can still flow through

the second P-channel MOSFET. Likewise, if any

cell voltage falls below the undervoltage limit, the

second P-channel MOSFET is turned off and only

charge current is allowed. Such a cell-voltage

condition causes the chip to go into low-power

sleep mode. Attempting to charge the battery

pack wakes up the chip. A cell-count pin (CLCNT)

is provided to program the IC for three- or four-cell

operations.

A two-tiered overcurrent controller and external

current shunt protect the battery pack from

excessive

discharge

currents.

If

the

first

overcurrent threshold level is exceeded, an

internal

timing

circuit

charges

an

external

capacitor to provide a user programmable

blanking time. If at the end of the blanking time the

overcurrent condition still exists, the external

discharge FET is turned off for a period 17 times

longer than the first blanking period, and then the

discharge FET is turned back on. If at any time a

second higher overcurrent threshold is exceeded

for more than a user programmable time, the

discharge FET is turned off, and remains off for the

same period as the first tier off time. This two tiered

overcurrent-protection

scheme

allows

for

charging capacitive loads while retaining effective

short-circuit protection.

1

2

3

4

5

6

7

8

16

15

14

13

12

11

10

9

VDD

CLCNT

WU

AN1

AN2

AN3

AN4

BATLO

DVDD

AVDD

CDLY2

DCHG

CHG

AN4

CDLY1

CHGEN

(TOP VIEW)

M PACKAGE

PRODUCTION DATA information is current as of publication date.

Products conform to specifications per the terms of Texas Instruments

standard warranty. Production processing does not necessarily include

testing of all parameters.

Copyright

 2002, Texas Instruments Incorporated

Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of Texas Instruments

semiconductor products and disclaimers thereto appears at the end of this data sheet.

Not Recommended for New Designs