beaglebone-black - Flipbook - Page 42
BeagleBone Black
6.1.8 Processor Interfaces
The processor interacts with the TPS65217C via several di昀昀erent signals. Each of these signals is described
below.
I2C0
I2C0 is the control interface between the processor and the TPS65217C. It allows the processor to control the
registers inside the TPS65217C for such things as voltage scaling and switching of the input rails.
PMIC_POWR_EN
On power up the VDD_RTC rail activates 昀椀rst. After the RTC circuitry in the processor has activated it instructs
the**TPS65217C** to initiate a full power up cycle by activating the PMIC_POWR_EN signal by taking it HI. When
powering down, the processor can take this pin low to start the power down process.
LDO_GOOD
This signal connects to the RTC_PORZn signal, RTC power on reset. The small n indicates that the signal is an
active low signal. Word processors seem to be unable to put a bar over a word so the **n* is commonly used
in electronics. As the RTC circuitry comes up 昀椀rst, this signal indicates that the LDOs, the 1.8V VRTC rail, is up
and stable. This starts the power up process.
PMIC_PGOOD
Once all the rails are up, the PMIC_PGOOD signal goes high. This releases the PORZn signal on the processor
which was holding the processor reset.
WAKEUP
The WAKEUP signal from the TPS65217C is connected to the EXT_WAKEUP signal on the processor. This is
used to wake up the processor when it is in a sleep mode. When an event is detected by the TPS65217C, such
as the power button being pressed, it generates this signal.
PMIC_INT
The PMIC_INT signal is an interrupt signal to the processor. Pressing the power button will send an interrupt to
the processor allowing it to implement a power down mode in an orderly fashion, go into sleep mode, or cause
it to wake up from a sleep mode. All of these require SW support.
6.1.9 Power Rails
VRTC Rail
The VRTC rail is a 1.8V rail that is the 昀椀rst rail to come up in the power sequencing. It provides power to the
RTC domain on the processor and the I/O rail of the TPS65217C. It can deliver up to 250mA maximum.
VDD_3V3A Rail
The VDD_3V3A rail is supplied by the TPS65217C and provides the 3.3V for the processor rails and can provide
up to 400mA.
VDD_3V3B Rail
The current supplied by the VDD_3V3A rail is not su昀케cient to power all of the 3.3V rails on the board. So a
second LDO is supplied, U4, a TL5209A, which sources the VDD_3V3B rail. It is powered up just after the
VDD_3V3A rail.
VDD_1V8 Rail
The VDD_1V8 rail can deliver up to 400mA and provides the power required for the 1.8V rails on the processor
and the HDMI framer. This rail is not accessible for use anywhere else on the board.
VDD_CORE Rail
The VDD_CORE rail can deliver up to 1.2A at 1.1V. This rail is not accessible for use anywhere else on the board
and connects only to the processor. This rail is 昀椀xed at 1.1V and should not be adjusted by SW using the PMIC.
If you do, then the processor will no longer work.
6.1. Power Section
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