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PGA460: Decay time variation with temperature

Furkan Fehmi Sefiloglu
Expert 3118 points
Part Number: PGA460

Hi Team,

Can you please check and advise with following request?

"

We use TI's PGA460 ultrasonic driver IC in a device we have developed. Although the schematic design, pcb and components of all the devices we produce are the same, the decay time (Ringing) value of the transducer increases more than the normal value in approximately 20% of the devices (up to 2000-3000 US) and this value also varies according to the temperature, Decay time (ringing) value is between 1200-1600 U.S, regardless of the temperature, in properly working devices, this situation sometimes creates a problem for us and we could not solve the source of the problem. In particular, we have doubts about the compatibility of the components shown in the picture below. Can you forward it to the relevant team for review of the circuit design?

"

Thanks in advance

Best Regards

Furkan Sefiloglu

  • 0
    TI__Mastermind 21010 points

    Furkan,

    I am not able to read the markings in the schematic you have included very well.  It is quite pixelated.  Can you upload again with better resolution?

    Thank you,

    Scott Bryson

  • 0
    Prodigy 40 points

    Hi Mr.Scott, 

    I'm the problem owner, I reached out Mr.furkan before and ask him for support. The schematic for PGA460 is below 
    https://ibb.co/vZzgj7w 

    We are using 400EP250 transcuder and 750317161 transformer with paralel 3k3 R and 3n9 C. Are there any design problems with that?

    Thanks in advance

  • 0 in reply to Scott Bryson
    TI__Expert 3118 points

    Hi Scott,

    Just updated schematic, can you please check and advise?

    Thanks in advance

    Furkan Sefiloglu

  • +1 in reply to Hasan Hatipoglu
    TI__Mastermind 21010 points

    Thank you for the updated drawing, this is much clearer and I was able to read the notes this time.  The variation here is not wholly unexpected given the transducer you have selected.  We have seen customers screen for this and even use this ring down time variation to grade out their product before.  What is really factoring in here are the tolerance variations on your components.

    One mode of verification on this, you might attempt to exchange the transducer and/or transformer from a good unit with one with long ring decay.  I would anticipate seeing the ring decay impacted by the part swap.

    We do normally see wider variation on 40 kHz transducers than with higher frequencies, but the concern here is that as you increase frequency you will also have a reduction in maximum range.

    In case you haven't already, it is good to do some evaluation on the resistor and capacitor values you have selected.  There's more details on this in the app note below:
    https://www.ti.com/lit/an/slaa732/slaa732.pdf

    Please take a look as this is a useful guide for working through hardware component selection.

  • 0 in reply to Scott Bryson
    Prodigy 40 points

    Hi,

    Thank you for your answer. We swapped some components between two boards, one of them with low and the other with high decay. We did it for 5 couples of devices. The exchanging of the transformer make large deference, I can say that the decay time in my case is depending on the transformer, even if we know that, it doesn't create a solution for our problem, we can't test all devices and replacing the transformer until finding the fit one. 

    Do you suggest another couple of transducer and transformer that have got a less tolerance variations ? (Preferring same transducer dimensions for mechanical reasons.)

    I checked out the app note and I notice that is recommended to use 100-2000pF for the parallel capacitor, we are using 3900pf. I don't think there is a problem with 3k3 dumping resistor we tuned it before to get a low decay time with good wave strength.

    Thanks is advance. 

  • +1 in reply to Hasan Hatipoglu
    TI__Mastermind 21010 points

    Hasan,

    We have a listing of possible candidate devices you might consider available here:

    https://www.ti.com/lit/zip/slac787

    The document does show some of the tolerance variations as they were available. You'll have to investigate which components are similar in size in order to fit your design. Hopefully this helps.  I do understand the difficulty with not being able to swap and test during manufacturing.

    Thanks,

    Scott