Motorola SSETM 5000 DC Power Routing-Transceiver Board, DC Power Routing-VOCON Board, V3A

Theory of Operation: Power Distribution 2-5

even when the On/Off/Volume knob has been turned to the off position, power remains on until the microcontroller unit (MCU) completes its power-down, at which time the radio is physically powered down.

2.3.1DC Power Routing—Transceiver Board

Connector J1, the B+ assembly, connects the battery to the transceiver board. Two capacitors provide protection against momentary breaks at the B+ connector due to contact bounce when the radio is dropped.

An RF bead forms a power-line filter for signal RAWB+, which supplies battery voltage to the transmitter PA.

A transistor, controlled by signal SWB+ from the VOCON board, turns on XB+, which supplies the 5-V linear regulator, TX_ALC block and SW_FL.

Fuse F901 and a filter supply fused B-plus to the VOCON board. In turn, the VOCON board supplies VSW1, regulated 3.8 Vdc, from the Global Control Audio and Power (GCAP) switching regulator to the XCVR. A switch, controlled by SWB+, turns on V38 to the XCVR 3-V linear regulators. The XCVR regulated power supplies are summarized in Table 2-3.

Table 2-3. Transceiver Voltage Regulators

IC	Output	Description
Name	Signal Name
LP2989	V5A	Regulated 5.0	Vdc
LP3985	V3D	Regulated 3.0	Vdc digital
LP3985	V3A	Regulated 3.0	Vdc analog for the RX FE

2.3.2DC Power Routing—VOCON Board

Raw B+, or unswitched B+, (UNSW_B+) is routed to connector J1 on the transceiver board, and then on to P201 on the VOCON board. Here the UNSW B+ is forwarded to the radio’s control top On/Off/Volume knob through connector J707 and a flex circuit, as well as to regulator U505 (VCC5).

The On/Off/Volume knob controls B+SENSE to a BJT switch, which in turn controls a power MOSFET. The MOSFET is a solid-state power switch that provides SW B+ to the VOCON board, the audio PA, the GCAP II IC (via GCAP_B+), and back to the transceiver board.

In the case of a secure radio model, SW B+ and UNSW B+ are also supplied to the encryption module through connector J701.

The BJT switch is also under the control of the MCU via Vref from the GCAP II IC (U501). This allows the MCU to follow an orderly power-down sequence when it senses that B+SENSE is off. This sense is provided through MECH_SW_BAR (inverted B+SENSE).

The digital circuits in the VOCON board are powered from regulators located in the GCAP II IC (U501), an external 5 Vdc regulator (VCC5, U505), and an external 1.55 Vdc regulator (VSW_1.55). The GCAP II IC provides three supplies: VSW1, VSW2, and V2. These regulators are software programmable.

6881094C12-A November 11, 2004