Pololu Orangutan SVP - Manual (Page 33)

11. USB Power
When connected to a computer, the USB connection provides a 5 V power supply. If an external power supply is
present, the unit will run off of the external supply and not draw any power from USB. If only the USB power is
present, then by default the auxiliary processor will be powered from USB, but the AVR and the VCC power pins
on the board will not be powered.
An option is available for powering the entire board from USB. To power the board from USB, install a jumper
to connect VUSB to VCC. When the board is powered this way, the voltage regulator will conduct current
backwards, resulting in a VBAT around 4.6 – 5.0 V and a VCC around 4.3 – 4.6 V. In some cases, VCC will be
low enough to trigger brown-out detection on the AVR. Therefore, if you are having trouble powering your AVR
from USB, try changing your brown-out detection fuses to be tolerant of lower voltages.
Using the VCC-VUSB jumper can also cause other problems because the Orangutan is not being USB-compliant
whenever it draws more than 100 mA from the USB. If the Orangutan draws too much power from USB, the host
may respond by disconnecting the power supply to that port. Therefore, if you are having trouble powering your
AVR from USB, you may be drawing too much power.
Pololu Orangutan SVP User's Guide © 2001–2012 Pololu Corporation
11. USB Power Page 33 of 37