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TPS650864: TPS6508640 BUCK2_POWER GOOD

user6251517
Prodigy 10 points
Part Number: TPS650864
Other Parts Discussed in Thread: TPS650861,

I have one question about TPS6508640:

We know, TPS6508640 has been programed by a default configuration before delivery to the customer.

the power up sequence is about:  LDO5 & LDO3P3------->  BUCK2 output +0V85  when CTL3 is high level--------------> other bucks output  when CTL4 is high level.

in my design, CL4 is connected to GPO1_BUCK2_PG, 

Now, LDO5 & LDO3P3 have no problem,  output normally,   and CTL3 is always high level,  but , the power good output of BUCK2 has some questions,

GPO1_BUCK2_PG will turn to low level and will keep 912uS low level  after a 17ms high level.  

if we cut off the load and we got the same result.   so, we think, there is some problem with TPS6508640.

it is hard for us to know why 0.85V will be powered down for about 912us and then will power up for about 17ms,  then power down again for 912uS,  and then power up and keep about 17ms......

Could you please help us about this question?

  • 0
    TI__Genius 17380 points

    Hello,

    You appear to be describing emergency shutdown followed by restart.

    The TPS650864 / TPS650861 family will initiate an emergency shutdown if any of the enabled voltage rails does not reach the target voltage within 10 ms.

    I would recommend going through the power up sequence described in Figure 6-4. TPS6508640 Power-Up Sequence in the datasheet and identifying if there is a power rails which is not reaching the target voltage as expected.

    An example of this behavior is in this E2E post where they figured out that they did not connect V5ANA so BUCK4 (the first of them to power on) was not stable: https://e2e.ti.com/support/power-management/f/196/t/893163

    Your case is likely to be a different power regulator. There are many possibilities. If you have not populated any of the external components for an "unused" power rail that is still being enabled by the sequencer, that would be a likely candidate. We have seen many cases where someone is not using one of the BUCKs and does not populate the inductor / capacitor. In that case the PMIC will see this as a power fault and do an emergency shutdown.

    If you are not able to identify the problem regulator, please post the screenshots of the power up sequence and we can analyze to see if there is anything you missed.