
D E M O 9 S 0 8 K B 1 2
N O V E M B E R
1 6 ,
2 0 0 9
U S E R G U I D E
CAUTION :
Do not configure the target board to draw more than 300mA when
powered from the integrated USB BDM. Damage to the target board or
host PC may result otherwise.
Power from the integrated BDM is drawn from the USB bus and is limited to 300 mA . This
current limit accounts for the total current supplied over the USB cable to the BDM circuit, the
target board, and any connected circuitry. Current drain in excess of value violates the USB
specification and will cause the USB bus to disconnect. This will cause the board to exhibit
power cycling where the board appears to turn off and back on continually. Damage to the
host PC or the target board may result.
Voltage input to the on-board regulator should be kept at or below +12V to prevent the
regulator from over heating.
VX_EN
The VX_EN option header is a 2-pin jumper that connects or disconnects input J1-1 directly to
the target board voltage rail. J1-3 connects directly to the target board ground plane. Use of
this feature requires a regulated input power source. This power input is decoupled to
minimize noise but is not regulated or protected. Care should be exercised when using this
feature; no protection is applied on this input and damage to the target board may result if
excessive voltage is applied. Also, do not attempt to power the target board through this
connector while also applying power through the USB BDM or the PWR connector; damage to
the board may result.
Power may also be sourced to off-board circuitry through the J1 connector. The current
supplied from the USB bus or the on-board regulator limits current available 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 header connections.
Figure 4: VX_EN Option Header
ON
OFF
1
2
Enabled
Disabled
VX_EN
CAUTION:
Do not exceed available current from USB-BDM or on-board regulator
when sourcing power through connector J1 to external circuitry.
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