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Original question:

TPS2373: Reference design ( TPS2373-3EVM-024 ) Application note for designing discrete parts

TPS2373: Reference design TIDA-050023

Janis Sarikas
Prodigy 155 points
Part Number: TPS2373

Hello, 

I have two questions regarding the reference design TIDA-050023

1. Why there are parts for slow start on the primary and secondary side (red boxes)? Is it not enough to use parts on the primary side?

2. Why there are parts for loop compensations on primary and secondary side (green boxes)? Is it not enough to use parts on secondary side?

Best regards

Janis

  • 0
    TI__Mastermind 21320 points

    Hello Janis, 

    1. We have found that with this design it is best practice to have both. In theory yes you could do just one, but it might be more exaggerated (like a larger cap or whatever). 

    I will say these two soft start processes are different, and limit the startup overshoot in different ways, so to me it is a more robust system but no issue having just the one. 

    2. Similar to above, in theory yes you could do one, but in practice i've never seen designs without it. Here, these components are setting poles and zeros in the feedback loop. If you feel confident that you can optimize your feedback loop for stability, I have no qualms but personally I've never seen it done. Many companies do not even carry bode boxes to test the system stability, so it really comes down to power compensation skills. 

    Personally, I've spent many weeks optimizing different boards and it is not a simple task, so I cannot recommend it. Also know the support on optimizing the design is going to be limited. 

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

     

    Regards, 

     

    Michael P.

    Applications Engineer

    Texas Instruments 

  • 0 in reply to Michael Pahl
    Prodigy 155 points

    Hello Michael, 

    thanks for your reply.

    1. Okay then I will use both of them for prototyping and check if one of them is enough. I guess looking for overshoots at the output voltage with high load after start up will verify it. Am I right? 

    2. Can you give me a hint how to calculate the additional poles and zeros for the primary side. I can't find proper design guide for this. All of the guides I found are only about secondary side compensation

    even the Powerstage-Designer tool only supports calculation for secondary side loop compensation. 

    Best regards

    Janis

  • 0 in reply to Janis Sarikas
    TI__Mastermind 21320 points

    Janis,

    https://www.ti.com/seclit/ml/slyp495/slyp495.pdf on slide 21 they show the equations for an optocoupler feedback design. you have to combine this with the typical type II error amplifier we use. 

    Again I strongly suggest using what is already in a design since it has been proven to work, and then tweak it if needed. 

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

     

    Regards, 

     

    Michael P.

    Applications Engineer

    Texas Instruments