Protection Devices; Automatic On/Off - Motorola CM160 Service Information

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Voltage regulator U503 provides 5V for the RF circuits. Input and output capacitors are used to
reduce the high frequency noise and provide proper operation during battery transients.
VSTBY is used only for CM360 5-tone radios.
The voltage VSTBY, which is derived directly from the supply voltage by components R5103 and
VR502, is used to buffer the internal RAM. Capacitor C5120 allows the battery voltage to be
disconnected for a couple of seconds without losing RAM parameters. Dual diode D501 prevents
radio circuitry from discharging this capacitor. When the supply voltage is applied to the radio,
C5120 is charged via R5103 and D501.
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 0.2V and turns On U514 and U501
9.3V regulator which supplies voltage to all other regulators and consequently turns the radio on,
When U504 (ASFIC_CMP) gets 3.3V, GCB2 goes to 3.3V 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
0.2V and turns on U514 and U501 9.3V regulator which supply voltage to all other regulators and
turns the radio on, When U504 (ASFIC_CMP) get 3.3V supply, GCB2 goes to 3.3V 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 0V from Ignition,
Q504 goes from Sat to Cut, ONOFF_SENSE goes to 3.3V and it indicates to the radio to soft turn
itself by changing GCB2 to '0' after de registration if necessary.
THEORY OF OPERATION