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Theory of Operation
DC Power Distribution
2 - 20
(See Figure 10).
V1 Linear Regulator
V1 is a programmable linear regulator. It is programmed using the Redcap SPI bus
from 0.975V to 3.0V in 8 steps. This regulator is active during Power Reset (POR)
and its initial value is 0.95V. For this radio, V1 (programmed to 1.875V) is the
supply for the vibrator motor. This regulator is active whenever the radio is turned
ON.
V2 Linear Regulator
V2 is a selectable linear regulator. It is selectable using the GCAP UV_SEL pin
between either 2.5V and 2.775V. This regulator is active during POR and its initial
output value is set by GCAP3 UV_SEL pin. Connecting UV_SEL pin to B+ sets
V2 output value to 2.775V, connecting UV_SEL pin to Ground sets V2 output val-
ue to 2.5V. For this radio, V2 is selected to 2.775V. This regulator is supplied by
B+ and it is active whenever the radio is turned ON. V2 is the supply for internal
and external audio circuits, CLK_IN input driver and TS interface.
V3 Linear Regulator
V3 is a selectable linear regulator. It is selectable using the Redcap SPI bus from
1.875V to 2.775V in 4 steps. This regulator is active during POR and its initial out-
put value is 2.775V. For this radio, V3 is selected to 2.775V. The regulator is sup-
plied by B+ and it is active whenever the radio is turned ON. V3 is V3_2.775V,
which is the supply for the SRAM, FLASH, Redcap, CE bus and Display.
V4 Linear Regulator
V4 is a selectable linear regulator with external pass transistor. It is selectable us-
ing the Redcap SPI bus from 1.875V to 2.775V in 4 steps. It is set to 2.775V. V4
is always powered from B+ and it is active whenever the radio is turned ON. This
regulator is active during POR. V4 is V4_2.775V_RF, which is the supply for the
WPIC, ODCT and LMX.
Switcher #1 (Synchronous Buck Mode Converter)
Switcher #1 is a selectable step down switching regulator. It is selectable using the
Redcap SPI bus from 1.2V to 2.45V in 6 steps, Pass Through and Power down
modes. The switcher is active during POR in 1.86V mode. It is set to 1.86V.
Switching regulator is PWM#1_1.86V, which is the supply for the internal core,
emulation port and clock output drivers of the Redcap. The switcher is supplied
from B+ and it is active whenever the radio is turned ON.
68P02963C70-O
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Troubleshooting
