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1-2

When the radio is turned on, SWB+ is present and is applied to:

transistor switch Q494 (pins 1 and 6) which turns on Q493

RX audio power amplifier U490

voltage divider R420/R421 and port PE0, a microprocessor A/D input which measures battery

voltage and radio on/off status

The output of FET switch Q493 is applied to the control pins of regulators U310, U320 and U330,

turning them on. The following regulators are used:

Reference No.

The 5V source is applied to:

RX back end circuitry

synthesizer super filter input and charge pump supply

RED/GRN LEDs

RX audio buffer U510

portions of ASFIC U451

The 5V source is also applied to FET switches Q311 and Q312. Q311 is turned on by Q313 when

RX_ENA (from U401 pin 49) is high, and supplies the "5R" source to the RF front end stages Q21-

Q22, and the VCO RX injection buffer Q280. Q312 is turned on by Q313 when TX_ENA (from U401

pin 50) is high, and supplies the "5T" source to the first transmitter stage Q100.

The digital 3.3 volt source from U320 (D_3.3V) is applied to:

microprocessor U401

EEPROM U402

S-RAM U403 (not used)

flash ROM U404

The 3V regulated source from U330 is applied to:

synthesizer IC U201

VCO/buffer IC U251

portions of ASFIC U451

microphone bias circuitry

While the radio is turned on, port PH3 (U401 pin 44) is held high. When the radio is turned off,

SWB+ is removed and port PE0 (U401 pin 67) goes low, initiating a power-down routine. Port PH3

(pin 44) remains high, keeping the voltage regulators on via Q493 and Q494, until the operating

state of the radio has been stored in EEPROM and other turn-off data functions have been

completed. PH3 then goes low, turning off Q494 and Q493, and all regulated voltages are removed.

Table 1-1 Voltage Regulators

Description

U310

5V Regulator

U320

Digital 3.3V Regulator

U330

3V Regulator

THEORY OF OPERATION

Type

TK71750S

LP2986

TK71730S