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TPS65217B What is the USB↑ sampling delay after OFF=1 and POWER_EN=0

Jonathan Asher
Intellectual 290 points
Other Parts Discussed in Thread: SYSCONFIG, TPS65217

I am trying to cause a AM335x system reboot from the SYSCONFIG peripheral after a software controlled shutdown (OFF=1 and POWER_EN=0). Using the AM335x RTC is not an option. I have 5.5V tied to the TPS65217B's AC input and a TPS76950 5V regulator tied to the USB input. The TPS76950 is enabled when LDO_PGOOD goes low at shutdown. The circuit functions as predicted but does not wake the TPS75217B even though the circuit meet the risetime requirements. Is there a delay period between the time LDO_PGOOD goes low and the wakeup (AC↑,USB↑,PB↓) conditions are sampled?

  • 0
    TI__Expert 4005 points

    1) If there is no battery present in the system, we do not recommend using both the AC and USB inputs. Please see page 25 of the datasheet.

    2) There is a 1 sec wait period from the time PWR_EN goes low to when the device enters the off state. During this time the device will not respond to wake up conditions.

  • 0 in reply to Gregory Watkins
    Intellectual 290 points

    I am aware of the 1 second delay and that is why I used the LDO_PGOOD going low to enable the TPS76950, I have also used the eventual powerdown of the LDO1 1.8V output to enable the TPS76950 with no luck.

    I have a super cap on the VBAT to provide hold-up power during a real power loss event to provide enough runtime for a controlled shut down. What I am thinking is that the USB↑ transition is occuring too soon after the LDO_PGOOD↓ transition.

    What I need to know is the exact parameter to delay the USB↑ after the LDO_PGOOD↓ transition to guarantee a automatic wakeup of the TPS65217B.

    The next PB↓ transition works but the system is designed to not require user intervention.

    I cannot use the TPS65217 Reset input because it is neccessary to have a controlled shutdown and then hard reboot just as if power was initially applied.