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TDMA StarTAC
CHRGC
ISENSE
SW_EXT_B+
BATT_FDBAK
BATT_FDBK_EN
2.75V
SRAM_VCC
B+
AUX_BATT+
SW_EXT_B+
Description
The internal charger will be activated only when there is an external power source, a Motorola battery is attached, the MAN_TEST line is loaded down, and
BATT_FDBK is enabled. As SW_EXT_B+ passes thru R1566, U1500(GCAP) reads the charge current for proper control of the charger. CHRGC controls the rate of
charge to the batteries by varying the gate biasing of Q1561. The output of Q1561 is split into two different sections. The one section is the BATT_FDBAK line.
BATT_FDBK_EN switches Q642 on or off to disable or enable BATT_FDBAK. When BATT_FDBK is not available, the external supply will lower it's supply to a
normal operating voltage and the internal charger will be turned. The second section is the line to charge the batteries. The radio is capable of charging two
batteries(Main and Auxiliary). The phone is designed to always charge the main battery first. Once the main battery is fully charged, it will begin charging the auxiliary
battery. Lines CHGR_MAIN_BATT and CHGR_AUX_BATT selects which battery will be charged. The dual transistor package Q600 has its outputs controlled by
CHGR_MAIN_BATT and CHGR_AUX_BATT. Each line out put of Q600 turns on or off charge transistors Q1562 and Q1563. When Q1562 is turned on, the main bat-
tery will be charged. When Q1563 is turned on, the auxiliary battery will be charged.
U1570(ABC) is used to select the B+ supply source of the radio. SW_EXT_B+ takes priority over any other source for the B+ power source. During this condition,
Q1570, Q1571, Q1572, and Q1573 are turned off, thus, having SW_EXT_B+ supply B+ thru CR1562. AUX_BATT+ is selected for the B+ power source if no
SW_EXT_B+ is present. During this condition, Q1572 and Q1573 is turned off and Q1570 and Q1571 is turned on, allowing AUX_BATT+ supply B+. MAIN_BATT+
is selected for the B+ power source if no EXT_B+ or AUX_BATT+ is present(or AUX_BATT+ is below minimum operating voltage). During this condition, Q1572 and
Q1573 is turned on and Q1570 and Q1571 is turned off allowing BATT+ supply B+.
In order for power cuts to operate correctly a B+ discharge circuit is required. B+ must discharge below 0.4V in 1 second. When the supply 2.75V is disabled(from a
power cut state) Q1574-A is turned on, thus turning on Q1574-B. When Q1574-B is turned on, B+ will be discharged through R1573. If the phone is in an on state,
Q1574-A is turned off, thus turning off Q1574-B. During this state B+ will not discharge through R1573.
TM
P8190:
R1566
Q1561
Q642
Q1574-A
R1573
Q1574-B
Q1571
CR1562
Charger/Batt Select
Q1562
Q600
Q1563
U1500
Q1572
Q1573
BATT+
CHGR_MAIN_BATT
CHGR_AUX_BATT
AUX_BATT+
AUX_BATT+
BATT+
BATT+
B+
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