UCC3957 1, UCC3957 2, UCC3957 3, UCC3957 4
SLUS236A 鈥?JANUARY 1999 鈥?REVISED JUNE 2001
THREE OR FOUR CELL LITHIUM ION
PROTECTOR CIRCUIT
FEATURES
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.
D
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Three- or Four-Cell Operation
Two-Tier Overcurrent Limiting
30-碌A(chǔ) Typical Supply-Current Consumption
3.5-碌A(chǔ) Typical Supply Current in Sleep Mode
Smart Discharge
Minimizes Losses in
Overcharge Mode
6.5-V to 20-V VDD Supply Range
Highly Accurate Internal Voltage Reference
Externally Adjustable Delays in Overcurrent
Controller
Detection of Loss-of-Cell Sense Connections
M PACKAGE
(TOP VIEW)
VDD
CLCNT
WU
AN1
AN2
AN3
AN4
BATLO
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3
4
5
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7
8
16
15
14
13
12
11
10
9
DVDD
AVDD
CDLY2
DCHG
CHG
AN4
CDLY1
CHGEN
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.
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
錚?/div>
2001, Texas Instruments Incorporated
www.ti.com
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