B+ And +5V Routing For Controller And Vocoder Boards - Motorola ASTRO XTS 3000 Service Manual

B+ and +5V Routing
for Controller and
Vocoder Boards
3-4
Refer to Figures 3-4 and 3-5 and the appropriate schematic diagrams.
Power for the radio is derived from a 7.5 volt battery, which is applied
to the transceiver board through J3. This Raw B+, or unswitched B+
(UNSW B+), is routed to J1 on the transceiver board and then on to
P201 on the controller board. Here the UNSW B+ is forwarded to the
radio's control top on/off/volume knob through J101 and a flex
circuit. The on/off/volume knob controls B+_SENSE to Q105, which in
turn controls Q106. Transistor Q106 is a solid-state power switch that
provides SW B+ to the controller and transceiver board's analog 5V
regulators, the audio PA, and back to the transceiver board. In
addition, UNSW B+ is routed to the main digital 5V regulator (U709);
B+ SENSE provides for enabling or disabling this regulator.
In the case of a secure radio model, SW B+ and UNSW B+ are also
supplied to the encryption module through J601.
Q106 is also under the control of the microcontrol unit (MC—-U701)
through a port on the SLIC IC (U702). This allows the MCU to follow
an orderly power-down sequence when it senses the SW B+ is off. This
sense is provided through the resistor network of R170 and R172,
which provides an input to the A/D port on the MCU.
The controller board contains two 5V regulators partitioned between
the digital logic circuitry and the analog circuitry. The 5V regulator for
the digital circuitry consists of U709, D104, L119, C180, and
associated components. This circuit is a switched mode regulator.
Switched mode regulators use a switched storage device (L119) to
supply just enough energy to the output to maintain regulation. This
allows for much greater efficiency and lower power dissipation. This
+5V digital supply powers all digital ICs on both the controller and
vocoder boards, as well as the display and keypad modules.
The analog circuitry of the ADSIC (U406) and the audio PA (U718) is
powered through a separate 5V linear regulator (U710).
It should also be noted that a system reset is provided by U726. This
device brings the system out of reset on power-up. It provides a system
reset to the microcomputer on power-down or if the digital 5V
regulator falls out of regulation.