U960 is a Charger control OverVoltage IC(COVIC). It is used to control the rate of charge to Nickel Metal Hydrid(NiMH) batteries that are ins talled in the transceiver.

U960 is al so used to control any excessively hi gh voltage conditions that can damage the transceiver.

EXT_B+ is the external supply from an accessory that is being used to allow the batteries to get charged. Q962 controls the rate of charge and is the disconnecting device to

the internal c ircuit of the phone if a hig h voltage(overvoltage) condition exists. U960 controls the rate of charge through Q962.

Three charging rates existsl;(1) trickel, (2) mainten ance, and (3) full. Trickel and mainten ance charging is controlled by the STUART(U1907) via the TRICKEL_SET line.

Full rate charging is controlled by the STUART(U1907) via the CHRG_EN line. The time period of charging the batteries is determined by monitoring the battery voltage.

The battery level is monitored in three categories; (1) 1/3 charge, (2) 1/2 charge, and (3) 3/4 charge. Each catergory will determine the tim e period of charge.

Once the charging rate has been determined, the batteries will be charged through Q18 12B. Q1812B also helps in pre venting reverse battery conditions.

If an over-voltage condition exists, Q962 needs to be completely turned off to protect the circuitry of the phone. The SENSE line in the U960 is used to determine whether

there is a over-voltage condition. If an overvoltage condition exists, the TRICKLE_SET and CHRG_EN ports in the U960 will be disabled . Having these two ports disabled

will not allow Q962 to be driven on.

The SENSE line is also used to detect a charging accessory. When a charging accessory is detected the PWRON line is pulled high. This will in form the GCAP(U1500) that

an external source is attached to the phone.

Having the PWRON high will also switch Q1598 on and allow the voltage to rise across C1589. C1589 will then discharge into the base of Q1597B. Q1597B will be

switched on during the discharge cycle of C1597. Switching Q1597B on will lower the base voltage of Q1597A and switch Q1597A on. Having Q1597A on will pull the

gate of Q1812A high , switching Q1812A into an off state. Q1812A will remain off until C1589 is discharged. This circuit design is used to prolong the accessory source

connection to the B+ lin e, giving U960 enough time to react to an overvoltage condition.

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