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TPS65131: 2x TPS65131 powered from a TPS63070

Christian Gunther
Prodigy 140 points
Part Number: TPS65131
Other Parts Discussed in Thread: TPS63070, TPS63030,

Hi! 

On my board I am using 2 dc dc converters configured to generate +15 V and - 15 V using exactly the components and pcb layout recommended by TI. The load connected to them draws max 110 mA on the negative and 135mA omn the positive. They are powered from a TPS63070 configured to deliver 5V, also, using exactly the components and pcb layout recommended by TI. My problem is that sometimes the positive of one or the other TPS65131 will be limited to the input voltage, no chopping. If I am disconecting the loads at startup, both work fine. If I connect in parallel both loads from each of the TPS65131 and leave the other one withot load, they will work. If I power the 2 TPS 65131 from and outside stronger power supply, they will start in any configuration. My problem: since a single TPA63070 obviously can generate enough current to drive all my loads if I connect them in parallel to any of my 2 x TPS65131, since, without loads, both of my TPS65131 are turning on, why is the current generated by the TPS63030 not sufficient to turn them on when each of the TPS65131 is driving a moderate load? Obviously, the 2 TPS65131 are influencing each other, but how, and how can I avoid that ?

  • 0
    TI__Intellectual 1965 points

    Hi Christian,

    I have notified our expert regarding this topic. Please expect a response by 2/20/19.

    Thanks,
    Grant

  • 0
    TI__Mastermind 18550 points
    Hello,

    Can you please attach schematics of your design so that we can review and try to figure out the reason for the issue you are seeing?
    Kind Regards,
    Liaqat
  • 0
    TI__Expert 7925 points
    Hi Christian,

    If you do not want to post the schematic/layout publicly, please send it to lbs_request@list.ti.com.

    Best regards,
    Milos
  • 0 in reply to Milos
    Prodigy 140 points

    Hi Milos!

    Just sent the schematics

    If you consider valid my sollution for the negative output having a higher value than it should and higher ripple, we could share it, as it works perfectly and I saw a lot of people complaining about similar problem and maybe they are in the same position like I am, pcb already finished without the filter, as that one was not mentioned in the application note, I found it later on the dev board...

    Best regards!

  • 0 in reply to Christian Gunther
    TI__Expert 7925 points
    Hi Christian,

    Thank you for the schematics.

    It might be that the 2xTPS65131 produce too much inrush current during startup when they are loaded, and that is too much for the TPS63070. Could you try delaying the startup of the 2xTPS65131 via their ENN/ENP pins? For the start you can do it with an external voltage directly connected to the ENN/ENP pins of TPS65131, and if this works then you can connect them to VIN via a RC network.

    As for the solution for the negative voltage this was not clear to me, but I guess this is TPS65131 related? In this case you might open a new thread, as this is different issue than we have here.

    Best regards,
    Milos
  • 0 in reply to Christian Gunther
    TI__Expert 7925 points
    Hi Christian,

    Just one additional question. How are you powering the TPS63070, and is there no current limiting due to source impedance, either by a power supply, a weak battery or long leads?

    Best regards,
    Milos
  • 0 in reply to Milos
    TI__Guru 65200 points
    Hello Christian,

    we haven’t heard back so we are assuming you were able to resolve your issue. If not, just post a reply below (or create a new thread if the thread has locked due to time-out) – Thanks