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WEBENCH® Tools/TPS62480: There is something wrong with the PG Pin of my TPS62480

Zun Niu
Prodigy 60 points
Part Number: TPS62480
Other Parts Discussed in Thread: TPS62180, , TMS320C6748

Tool/software: WEBENCH® Design Tools

Hi, I want to power TMS320C6748. I use TPS62480 to output 1.23V and TPS62180 to output 1.8V.  The device should be powered- on in order, so I connect the PG pin of TPS62480 with the EN pin of TPS62180 so that we can get 1.23V before 1.8V. However, there is something wrong with the PG Pin of my TPS62480. I find the output of TPS62480 is right: 1.23V but TPS62180 can't output 1.8V.  I also find TPS62180 works well only after I measure the voltage of the PG Pin with my Voltmeter. The schematic is as the auxiliary， could you help me？  

  • 0
    TI__Mastermind 35115 points

    Hi Zun,

    Based on the "OPT" text on the value of 1R14 am I right in assuming it is not populated?

    The issue may be related to the relatively large 470 kΩ pull-up resistor on the PG pin to only 1.23 V. When the EN pin of the TPS62180 is near the 1.0 V threshold, the pull-up current from this would be only ~400 nA. When you probe the PG pin it might be providing some additional pull-up and help the voltage get above the EN threshold.

    I suggest trying to either use 1R14 as the pull-up OR reduce 1R15 by 1/10th to 47 kΩ. When the PG pin is near 1 V, using 1R14 as the pull-up would provide 8.4 µA pull-up current and decreasing 1R15 to 47 kΩ would provide ~3.6 µA pull-up current.

  • 0 in reply to Anthony F
    TI__Mastermind 35115 points

    Hi Zun,

    Did my recommendations resolve the problem? Let me know if you need any further help with this.

  • 0 in reply to Anthony F
    TI__Mastermind 35115 points

    Hi Zun,

    I am going to mark this as resolved for now. If you still need help, you can just reply to this thread.