M 5 2 2 2 1 D E M O U S E R G U I D E
J A N U A R Y 1 8 , 2 0 0 7
12
Power Indicators
The +3.3V LED shows when the +3.3V rail is energized. Located on the output of the ON/OFF
switch, the +3.3V LED illuminates when the board is energized regardless of power input
source. The +5V LED shows when the +5V rail is energized.
POWER SWITCH
The ON/OFF switch connects and disconnects all input sources to the +3.3V rail. In the OFF
position, no voltage is present on the +3.3V rail. In the ON position, the input voltage source is
connected to the +3.3V rail.
Figure 4: PWR_SW Switch
PWR_SW
CONFIGURATION
OFF - Input power source disconnected from +3.3V rail
PWR_SW
ON - Input power source connected to +3.3V rail
POWER SELECT
Two option headers control input power configuration for the M52221DEMO. The PWR_SEL
header selects between the on-board, +3.3V, regulator and the USB BDM voltage input. The
VX_EN header connects J1-1 directly to the +3.3V rail. The sections below show the different
configuration for each option header.
PWR_SEL
Power from the integrated USB BDM is drawn from the USB bus and is limited to
500mA
. Ex-
cessive current drain will violate the USB specification causing the USB bus to disconnect.
CAUTION:
Violating the USB specification will cause the USB bus to disconnect. This will
cause the board to reset.
Both on-board voltage regulators accept power input through a 2.1mm barrel connector
(PWR). Input voltage may range from +6V to +15V. VR1 provides a +3.3V fixed voltage out-
put (VDD) with output current limited to 800mA. Over-temperature and over-current limit built
into the voltage regulator provides limited protection from damage due to excessive stresses.
The user should consider the maximum output current of the selected power source when at-
tempting to power off-board circuitry through connector J1.
