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TPS23753A: PMP8803 ILed current

Pjs
Intellectual 870 points
Part Number: TPS23753A
Other Parts Discussed in Thread: PMP8803

Hi, 

I'm testing the PMP8803 design and I'm finding I'm only getting an output of 7.8V under no load rather than 12V as per the design.

The only fix I've found is by reducing the Iled current. The design uses 4mA iLed with 2.5mA bias on the primary side - does this sound about right for a 80-160% CTR? I'm finding that reducing the Iled to around 2mA and the output restores to 12V. 

There might be some other issue in my testing but I've not found it yet and the 4mA iLed looked quite high compared to other TI designs I've seen. 

Many thanks

  • +1
    TI__Mastermind 21320 points

    Hey Phil, 

    I think this is a reasonable change, this will affect the compensation loop beyond just the opto CTR since it changes the gain ratio in the feedback equation. It should only affect the loop compensation, so also want to check the load transient performance too. 

    I sent Albert the EVM test list that we can run through for the design. 

    If this post answers your question, please indicate so by marking this thread as resolved. Thank you.

     

    Regards, 

     

    Michael P.

    Applications Engineer

    Texas Instruments