UCC3957 -1/-2/-3/-4

PRELIMINARY

SLUS236 - JANUARY 1999

FEATURES

• Three or Four Cell Operation

• Two Tier Overcurrent Limiting

• 30µA Typical Supply Current

Consumption

• 3.5µA Typical Supply Current in Sleep

Mode

• Smart Discharge Minimizes Losses in

Overcharge Mode

• 6.5V to 20V VDD Supply Range

• Highly Accurate Internal Voltage

Reference

• Externally Adjustable Delays in

Overcurrent Controller

• Detection of Loss of Cell Sense

Connections

Three - Four Cell Lithium-Ion Protector Circuit

BLOCK DIAGRAM

UDG-97060

DESCRIPTION

The UCC3957 is a BiCMOS three or four cell lithium-ion battery pack

protector designed to operate with external P-channel MOSFETs. Uti-

lizing 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 over-

charge and overdischarge. A separate overcurrent protection block pro-

tects the battery pack from excessive discharge currents.

If any cell voltage exceeds the overvoltage threshold, the appropriate ex-

ternal P-channel MOSFET is turned off, preventing further charge cur-

rent. 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 PFET. Likewise, if any cell voltage falls below the undervoltage

limit, the second P-channel MOSFET is turned off and only charge cur-

rent is allowed. Such a cell voltage condition will cause the chip to go

into low power sleep mode. Attempting to charge the battery pack will

wake 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.

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