LM3S2939 Datasheet, PDF (177/749 Pages) Texas Instruments – Stellaris® LM3S2939 Microcontroller

Stellaris^® LM3S2939 Microcontroller
5.2.3
Power Control
The Stellaris^® microcontroller provides an integrated LDO regulator that is used to provide power
to the majority of the controller's internal logic. For power reduction, the LDO regulator provides
software a mechanism to adjust the regulated value, in small increments (VSTEP), over the range
of 2.25 V to 2.75 V (inclusive)—or 2.5 V ± 10%. The adjustment is made by changing the value of
the VADJ field in the LDO Power Control (LDOPCTL) register.
Figure 5-4 on page 177 shows the power architecture.
Note: On the printed circuit board, use the LDO output as the source of VDD25 input. Do not use
an external regulator to supply the voltage to VDD25. In addition, the LDO requires decoupling
capacitors. See “On-Chip Low Drop-Out (LDO) Regulator Characteristics” on page 697.
VDDA must be supplied with 3.3 V, or the microcontroller does not function properly. VDDA
is the supply for all of the analog circuitry on the device, including the LDO and the clock
circuitry.
Figure 5-4. Power Architecture
VDD25
VDD25
VDD25
VDD25
LDO
Internal
Logic and PLL
GND
GND
GND
GND
Low-noise
LDO
+3.3V
VDDA
VDDA
Analog circuits
GNDA
GNDA
VDD
GND
VDD
GND
VDD
I/O Buffers
GND
VDD
GND
June 18, 2012
177
Texas Instruments-Production Data