Motorola SSETM 5000 - Manual (Page 27)

6881094C12-A November 11, 2004
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.
2.3.1 DC 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 .
2.3.2 DC 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.
Table 2-3. Transceiver Voltage Regulators
IC
Name
Output
Signal Name
Description
LP2989 V5A Regulated 5.0 Vdc
LP3985 V3D Regulated 3.0 Vdc digital
LP3985 V3A Regulated 3.0 Vdc analog for the RX FE