TP9100 Service Manual Circuit Descriptions 65
© Tait Electronics Limited May 2005
3.6 Power Supply Circuitry
Introduction For a block diagram of the power supply circuitry, refer to Figure 3.6.
Internal Power
Supplies
The radio has the following internal power supplies:
■ Two 5V regulators are connected to the +7V5 LINK supply and generate
the voltages +5
V0 TX and +5V0 AN.
■ A 3V3 SMPS regulates the +7V5 BATT supply to +3V3.
■ A 1V5 SMPS regulates the +3V3 of the 3V3 SMPS to +1V5.
■ Three linear regulators (3V, 2V5, 1V8) regulate the +3V3 of the
3V3 SMPS to +3
V0 AN, +2V5 , +1V8). These linear regulators take
advantage of the efficiency gain of the 3V3 SMPS.
■ The 3V RX switch switches the +3V0 AN of the 3V linear regulator to
+3
V0 RX. The 3V RX switch uses a P-channel MOSFET.
Power-Up Circuitry When the ON/OFF switch (RV1) is turned on, a short pulse of approximately
35ms is generated via C634 on the base of the NPN transistor Q606,
turning it on. This turns on the PNP transistor and charges C620. After the
short pulse, C610 can hold the 3V3 SMPS (IC610) for a further
approximately 2.5s (a voltage higher than approximately 1V on pin 1 turns
this regulator on). This regulator supplies the digital circuitry, and the
software asserts the
DIG PSU LATCH signal. This signal holds the transistors and
keeps C610 charged. The benefit of keeping the transistor charged is that in
case of a reset (due to a watchdog timeout or power supply spike) the radio
has 2.4s to recover (including rebooting and reasserting
DIG PSU LATCH) and
does not turn off.
It is also possible to power up the radio by the method described above
(except via C634) when the battery is attached.
PSU Supervisor The PSU supervisor monitors the +3V3 of the SMPS. It comprises a reset
and watchdog timer, and provides the reset signal
PSU SYS RST to the digital
section, which in turn provides the watchdog signal
DIG WD KICK required by
the PSU supervisor.
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