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
13
Figure 5: PWR_SEL Option Header
•
•
•
Select power input from USB BDM
VB
VDD
PWR_SEL
•
•
•
Select power input from VR1
VB
VDD
PWR_SEL
VX_EN
A 2-pin option header, VX_EN, connects input J1-1 directly to the +3.3V rail. J1-3 is connected
directly to the ground plane. This input requires a reg3.3V voltage source. This power
input is decoupled to minimize noise input but is not regulated. Also, no protection is applied
on this input and damage to the target board may result if over-driven. Do not attempt to
power the target board through this connector while also applying power through the USB
BDM or the PWR connector as damage to the board may result.
Power may be sourced to off-board circuitry through the J1 connector. The current limitation of
the USB bus or the on-board regulator must be considered when attempting to source power
to external circuitry. Excessive current drain may damage the target board, the host PC USB
hub, or the on-board regulator. The figure below details the VX_EN option header connec-
tions.
Figure 6. VX_EN Option Header
ON
Enable power connection to connector J1
VX_EN
▪
▪
OFF
Disable power connection to connector J1
VX_EN
CAUTION:
Do not apply power to connector J1 while also sourcing power from either the PWR
connector or the USB BDM circuit. Damage to the board may result.
NOTE
: Do not exceed available current supply from USB BDM cable or on-board regulator
when sourcing power through connector J1 to external circuitry.
USB OTG Power
The M52221DEMO is not designed to draw power from the USB cable connected to the MAB
connector at J2. Power output to the USB MAB connector is provided by a high-side switch
located at U2. This device provides the +5V output necessary for proper operation of the bus
when the board is in host mode. The ILIM option header sets the output current limit. Current
output is selectable between either 100 mA or 500 mA
