Motorola PM400 Service Manual download pdf (Page 169)

2-10 THEORY OF OPERATION

Voltage regulator U503 provides 5 V for the RF circuits. Input and output capacitors are used to

reduce the high frequency noise and provide proper operation during battery transients.

5.2 Protection Devices

Diode VR500 acts as protection against ESD, wrong polarity of the supply voltage, and load dump.

VR692 - VR699 are for ESD protection.

5.3 Automatic On/Off

The radio can be switched ON in any one of the following three ways:

• On/Off switch. (No Ignition Mode)

• Ignition and On/Off switch (Ignition Mode)

• Emergency

5.3.1 No Ignition Mode

When the radio is connected to the car battery for the first time, Q500 will be in saturation, Q503 will

cut-off, Filt_B+ will pass through R5073, D500, and S5010-pin 6 (On/Off switch). When S5010 is

ON, Filt_B+ will pass through S5010-pin5, D511, R5069, R5037 and base of Q505 and move Q505

into saturation. This pulls U501-pin2 through R5038, D502 to 0.2 V and turns On U514 and U501

9.3 V regulator which supplies voltage to all other regulators and consequently turns the radio on,

When U504 (ASFIC_CMP) gets 3.3 V, GCB2 goes to 3.3 V and holds Q505 in saturation, for soft

turn off.

5.3.2 Ignition Mode

When ignition is connected for the first time, it will force high current through Q500 collector, This

will move Q500 out of saturation and consequently Q503 will cut-off. S5010 pin 6 will get ignition

voltage through R601 (for load dump), R610, (R610 & C678 are for ESD protection), VR501,

R5074, and D500. When S5010 is ON, Filt_B+ passes through S5010-pin 5, D511, R5069, R5037

and base of Q505 and inserts Q505 into saturation. This pulls U501-pin 2 through R5038, D502 to

0.2 V and turns on U514 and U501 9.3 V regulator which supply voltage to all other regulators and

turns the radio on, When U504 (ASFIC_CMP) get 3.3 V supply, GCB2 goes to 3.3 V and holds

Q505 in saturation state to allow soft turn off.

When ignition is off Q500, Q503 will stay at the same state so S5010 pin 6 will get 0 V from Ignition,

Q504 goes from Sat to Cut, ONOFF_SENSE goes to 3.3 V and it indicates to the radio to soft turn

itself by changing GCB2 to ‘0’ after de registration if necessary.

5.3.3 Emergency Mode

The emergency switch (P1 pin 9), when engaged, grounds the base of Q506 via EMERGENCY

_ACCES_CONN. This switches Q506 to off and consequently resistor R5020 pulls the collector of

Q506 and the base of Q506 to levels above 2 volts. Transistor Q502 switches on and pulls U501

pin2 to ground level, thus turning ON the radio. When the emergency switch is released R5030 pulls

the base of Q506 up to 0.6 volts. This causes the collector of transistor Q506 to go low (0.2 V),

thereby switching Q502 to off.

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Motorola PM400 Service Manual Page 169