• State Resolved
  • Locked Locked
  • Replies 3 replies
  • Subscribers 63 subscribers
  • Views 252 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TPS2819: VCC oscillation

Kazuki Itoh
Genius 10730 points
Part Number: TPS2819
Other Parts Discussed in Thread: TPS2829

Hi team,

 

My customer is trying to use TPS2819 with the external 13.7V supply from LDO.

VDD and VCC are tied as well as Figure 20 in the datasheet because the customer doesn’t want to use the internal regulator.

300ms after LDO’s start-up,  VCC started to oscillate and the voltage went down from 13.7V to 12.3V.

Could you help me to address this issue?

 

Regards,

Itoh

  • 0
    TI__Genius 11770 points

    Hello Itoh-san,

    Oscillation/stability can be a common problem when connecting LDO outputs like this. This document is for a slightly different application, but some of the techniques may help. I assume this behavior was seen with no load? Turning on the output of the driver may actually fix the issue with no changes. If not, a "dummy load" or increasing the VCC capacitance could help the stability. 

    The system should pull to the higher voltage and effectively disable the internal LDO. Please let me know if the customer can implement any of these suggestions and if they work for our future reference.

    Thanks,

    Alex M.

  • 0 in reply to Alexander Mazany
    TI__Genius 10730 points

    Hi Alex-san,

    Increasing VCC cap didn't work to avoid the oscillation.

    Could you let me know how high input voltage is sufficient to avoid the oscillation?

    Or, does migration to TPS2829 or cutting off VDD path work as a solution?

    Regards,

    Itoh

        

  • +1 in reply to Kazuki Itoh
    TI__Genius 11770 points

    Hello Itoh-san,

    Sorry to hear that didn't work. There is an internal diode that makes a path from VCC to VDD that should ensure that VDD is out of regulation due to the drop. I think separating the external short from the VDD path could help, and is worth evaluating. Switching to TPS2829 is essentially doing the same thing but without the VDD pin bonded out. Therefore, moving to TPS2829 is likely a better solution for noise, but separating out VDD should work also. 

    There are also drivers like the UCC2751x family which have p2p or nearly p2p layouts with better cost and supply, especially long term because the TPS28xx is so old. So those are worth considering also. 

    Please let me know if separating out the VDD/VCC helps for our future reference.

    Thanks,

    Alex M.