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TPS3620: Vout operation

Mark Guastaferro
Genius 11645 points
Part Number: TPS3620

TPS3620-33 is being used to manage the input voltage to a 3.0V LDO.  VDD input = 3.6V, Vbat input = 3.3V.  Capacitance on TPS3620 Vout pin totals 33 mF. This design has been used for many years on multiple projects.

Customer reports that the LDO voltage will lose output sometimes and the suspicion is that some transient condition on the TPS3620 inputs is causing its Vout to drop. Its possible that the VDD or VBAT input is turning on/off at a 10Hz rate. Would one of the inputs switching like this or not being stable cause an issue with the TPS3620? Right now it is not known if the circuit is on long enough to fully charge the large output cap, so its possible Vout is still ramping when this happens. 

Based on the TPS3620 data sheet, it seems Vout should always be connected to either VDD or VBAT. Are there any input conditions that could cause Vout to drop out? 

  • 0
    TI__Genius 9375 points
    Mark,

    Based on the timing diagram in the datasheet, the Vout is always either VDD or VBAT and will only drop low if both power sources are low. Because of this, it seems like the issue might be VDD and VBAT both going low at some point while switching; do you know if this is happening at any point?

    Thanks,
    Abhinav
  • 0 in reply to Abhinav.Sharma
    TI__Genius 11645 points
    Hi Abhinav,
    The issue has been difficult to reproduce so we don't have good details at this time. We don't think both inputs are dropping at the same time. the customer is basically asking if we know any other reason this could happen.
    Is there any way to simulate the TPS3620? I don't see a Pspice or TINA model available online, or even an eval board.
  • 0 in reply to Mark Guastaferro
    TI__Genius 9375 points
    Mark,

    We're not aware of any miscellaneous consequences that can cause a drop on the output like this. Can the customer provide any scope outputs that could shed some light on the issue? The only other thing could be a bad part - do you know whether they've tested this on multiple units?

    There's no way to simulate the TPS3620 but we have a bench setup we can run if we get some more info on their exact setup - maybe we can replicate it.

    Thanks,
    Abhinav
  • 0 in reply to Abhinav.Sharma
    TI__Genius 11645 points
    Hi Abhinav,
    I'm going to take this offline and send you an email directly with more details and possible tests you could try.