Operator's Manual

CIRCUIT DESCRIPTION
4-4
September 2001
Part No. 001-5100-001
4.2 POWER SUPPLY
4.2.1 GENERAL
The radio is typically powered by a battery which
is fastened at the back of the radio. The electrical
contact between the battery and the radio occurs on
probes located on the Digital board (see Figure 4-1).
However the positive battery voltage (UNSWB+) is
directly routed through a small flex circuit (Power
Flex) to contacts located on the bottom of the RF
Board.
The UNSWB+ signal is then routed to the RF
power amplifier module and ALC IC on the RF Board.
It also passes through a fuse and is then routed to the
Digital Board.
The UNSWB+ signal passes through the Digital
Board without being used and is transferred to the
Keypad Board. On the keypad board, the UNSWB+
signal is routed as follows:
• Input of the 5V digital regulator
• Electronic switch which controls the input of the 5V
analog regulator and the “switched RF B+”
• “On/off switch” located on the top of the radio
• Low voltage detector
• Audio amplifier power FET
4.2.2 POWER ON OPERATION
When the user turns the radio on using the top
panel “on/off switch”, the following sequence of
events occur:
1. Power is applied to the shutdown pin of the 5V
digital regulator.
2. The 5-volt digital supply is created.
3. The appearance of the 5V digital supply turns on the
electronic switch which applies the battery voltage
to the “Switched RF B+” line and to the input of the
5V analog regulator.
4. The 5-volt analog supply is created.
5. If the battery voltage is high enough, the low voltage
detector output goes high.
6. The controller sets the control line to the shutdown
pin of the DC/DC converter to a high level.
7. The controller sets the radio in an operational mode.
4.2.3 POWER OFF OPERATION
When the user turns the radio off using the top
panel “on/off switch”, the following sequence of
events occur:
1. The “on/off switch” opens.
2. Power is removed from the shutdown pin of the 5V
DC/DC converter.
3. The controller detects that the power is off through
the pin connected to Switched B+.
4. The controller performs all required save
operations.
5. The controller resets the control line to the shut-
down pin of the DC/DC converter.
6. The 5-volt Digital source disappears.
7. The electronic switch opens.
8. The switched RF B+ and 5V analog sources
disappear.
4.2.4 LOW VOLTAGE DETECT
Low battery voltage is detected by a comparator
chip. When a low voltage condition is detected (less
than 6.3V), the following actions occur:
1. The low voltage detector output goes low which
alerts the controller.
2. The controller prevents any action which could have
a damaging effect (like writing in flash memory).
3. The controller releases its control of the shutdown
pin of the DC/DC converter.
4. The transmitter switches to the low power mode.