beaglebone-black - Flipbook - Page 39
BeagleBone Black
Fig. 6.4: TPS65217 DC Connection
6.1.3 USB Power
The board can also be powered from the USB port. A typical USB port is limited to 500mA max. When powering
from the USB port, the VDD_5V rail is not provided to the expansion headers, so capes that require the 5V rail
to supply the cape direct, bypassing the TPS65217C, will not have that rail available for use. The 5VDC supply
from the USB port is provided on the SYS_5V, the one that comes from the**TPS65217C**, rail of the expansion
header for use by a cape. Figure 24 is the connection of the USB power input on the PMIC.
6.1.4 Power Selection
The selection of either the 5VDC or the USB as the power source is handled internally to the TPS65217C and
automatically switches to 5VDC power if both are connected. SW can change the power con昀椀guration via the
I2C interface from the processor. In addition, the SW can read the**TPS65217C** and determine if the board
is running on the 5VDC input or the USB input. This can be bene昀椀cial to know the capability of the board to
supply current for things like operating frequency and expansion cards.
It is possible to power the board from the USB input and then connect the DC power supply. The board will
switch over automatically to the DC input.
6.1.5 Power Button
A power button is connected to the input of the TPS65217C. This is a momentary switch, the same type of
switch used for reset and boot selection on the board.
If you push the button the TPS65217C will send an interrupt to the processor. It is up to the processor to then
pull the**PMIC_POWER_EN** pin low at the correct time to power down the board. At this point, the PMIC is
still active, assuming that the power input was not removed. Pressing the power button will cause the board
to power up again if the processor puts the board in the power o昀昀 mode.
34
Chapter 6. Detailed Hardware Design
