UCC3957-2

Features:

` Three or Four Cell Operation
` Two Tier Overcurrent Limiting
` 30A Typical Supply Current Consumption
` 3.5A 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


Pinout




Specifications

Supply Voltage  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20V
Supply Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25mA
Output Current (CHG, DCHG)   . . . . . . . . . . . . . . . . . . . . . 25mA
WU Input Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28V
BATLO Input Voltage . . . . . . . . . . . . . . . . . . . . . . 0.3V to 2.5V
AN1 and AN3 Input Voltage   . . . . . . . . . . . . . . . . . VAN4 VDD
CLCNT and CHGEN     . . . . . . . . . . . . . . . . . . . . . . . VAN4 VDD
Storage Temperature . . . . . . . . . . . . . . . . . . . 65°C to +150
Junction Temperature. . . . . . . . . . . . . . . . . . . 55°C to +150
Lead Temperature (Soldering, 10 sec.)   . . . . . . . . . . . . . +300

Unless otherwise indicated, voltages are referenced to AN4. Currents are positive into, negative out of the specified terminal. Consult Packaging Section of Databook for thermal limitations and considerations of packages.


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 UCC3957 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 PFET. 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 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.

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 will remain 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.