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TAS5558: Differential PWM pairs termination

Andrew Miller60
Prodigy 50 points
Part Number: TAS5558
Other Parts Discussed in Thread: TAS5624A

Hello,

I have a design application using the TAS5558 with a TAS5624A amplifier with (2N) BTL and AD modulation. Regarding driving the differential PWM into a 8 inch backplane with opto-isolation does TI recommend tightly or loosely coupled differential pairs and what termination if any?

Best Regards, AM

  • 0
    TI__Guru 62720 points
    Andrew,

    I'm not sure what you mean by "8 inch backplane", could you elaborate please? The differential coupling is not very specific on these devices as the speed is relatively low. On our EVMs containing the part we do not do length matching or 50-ohm trace control. We simply try route the signals together with reasonable relative lengths. We have boards with the modulator and powerstage on the same board, as well as boards that have them separated by a longer cable. Neither show issues.

    Generally the only termination we use is a ~50ohm resistor in series with the PWM signals between the modulator and the powerstage.

    Regards,

    -Adam
  • 0 in reply to Adam Sidelsky
    Prodigy 50 points

    Thanks for the great answer Adam, 8" refers to the trace length. One last question: To provide the differential PWM using (2N) BTL AD modulation for the TAS5624A amp is it possible to take only one positive PWM output from the TAS5558, invert it and the use the positive and inverted signals for the INPUT_A and INPUT_B PWM inputs for the TAS5624A ?

    Best Regards ,  AM

  • 0 in reply to Andrew Miller60
    TI__Guru 62720 points
    Andrew,

    Yes you can! We do this on some of our boards. Ideally you would use the outputs directly from the TAS5558 since you can then leverage the smart features of the modulator but it can be done your way.

    Please click the "This resolved my issue" button if your questions are answered.

    Regards,

    -Adam