Voltage Regulation; Voltage Regulators - Motorola MCS 2000 Service Instructions Manual

Voltage
Regulation

Voltage Regulators

7-2 Controller Section Theory of Operation
The radio controller consists of 5 main functional sections. These are:

• voltage regulation

• power control
• interfacing
• microprocessor operation
• audio and signalling processing
The controller is based on the Motorola 68HC11F1 microprocessor (U0103).
In addition to the microprocessor, the controller has 3 external memory
devices, signal MUX IC (U0105), and a Support Logic IC (SLIC IV, SLIC IVa, or
SLIC V, U0104). The 3 memory devices consist of a 32 Kbyte EEPROM (U0100),
32 Kbyte SRAM (U0101), and a 256Kbyte or 1MByte FLASH EEPROM (U0102).
The digital section consists of a microprocessor, support memory, support
logic, signal MUX ICs, the On/Off circuit, and General Purpose Input/Output
circuitry.
(Refer to schematic page 10-29 or 10-30 for reference)
Voltage regulation for the controller is provided by 4 separate devices; U0500
(LM2925) +5V, U0501 (LM2941) +9.3 V, U0502 +8V, and UNSW 5V (a
combination of R0004 and VR0001). Additional regulators are located in the
RF section and the control head/handset.
Voltage regulation providing 5V for the digital circuitry is done by U500. Input
and output capacitors (C0500/0501 and C0503/0504) are used to reduce high
frequency noise and provide proper operation during battery transients. This
regulator provides a reset output (pin 5) that goes to 0 volts if the regulator
output goes out of regulation. This is used to reset the controller during power
on to prevent improper operation. C0502 sets the duration of this reset signal
to a minimum of about 12 ms.
Regulator U0501 is used to generate the 9.3 volts required by some audio
circuits, the RF circuitry and power control circuitry. Input and output
capacitors (C0505/0506 and C0508/0509) are used to reduce high frequency
noise. R0503/R0504 sets the output voltage of the regulator. If the voltage at
pin 1 is greater than 1.2 volts the regulator output decreases and if the voltage
is less than 1.2 volts the regulator output increases. This regulator output is
electronically enabled by a 0 volt signal on pin 2. Q0500 and associated
circuitry (R0500/0501/0502 and C0507) are used to disable the regulator when
the radio is turned off.
Regulated 8V is provided by U0502. It provides a separate supply to the
microphone circuitry. The microphone cannot be supported directly from A+/
SWB+ because any fluctuation on A+ would be impressed on the microphone
line and affect transmitted audio. The microphone circuitry can not be
connected to the other regulators because, there is a function which allows the
radio to be switched on by momentarily grounding the microphone line (see
Electronic On/Off).