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Ground Break Circuit App Note SLOA143

Robert McKellar16394
Prodigy 20 points

Other Parts Discussed in Thread: TPA6136A2, INA134, TPA6132A2, INA2134

Hi guys

The recent App Note deals mainly with reducing shield current by adding a resistor to the drive circuit between shield and ground.

I am designing a x16 mono channel receiver and have no control over the drive circuit. I have a couple of questions.

Q1: Can I use the TPA6136A2 as a line receiver, inserting a 10R resistor between shield and SGND to achieve ground break?

Q2: If I use LIN- for Ch1 and RIN- for Ch2, is it OK to connect both shields to the same ground break resistor?

Q3: As SGND on the TPA6136A2 is connected to the resistor divider network driving the non-inverting inputs, can I instead use an INA134 per channel with the ground break resistor connected between the shield input and pin 1?

Thank you in advance for your help.

Bob

  • 0
    TI__Mastermind 18510 points

    Robert, I’m happy to say that the paper includes information for applications like yours.  Here’s where to look.

    Q1)  TPA6132A2 can work very well to implement a pair of mono line drivers.  See the schematic in section B.2 on page 11 of the paper, and note the connections from the 2 "Rs" to Rgbk.  Of course, the schematic illustrates a stereo input.  Rgbk connections will be different for mono inputs (next question).

    Q2)  Mono sources require a separate Rgbk for each input.  The individual mono sources are likely to have different ground potentials with respect to the receiver, so the resulting shield currents are likely to be different.  A common Rgbk sums shield currents for rejection, and rejection will be correct for the sum, but it’s unlikely to be correct for the individual shield currents.  (Of course, for a 3-wire stereo connection like a standard 3.5mm stereo audio cable, the shield sides of 2 inputs would be connected together.)

    Q3)  INA134 or INA2134, the 2-channel version, would be good for this application.  Pin 3 of INA134 (or pins 3 and 5 of INA2134) should be connected to the junction of the input shield and Rgbk, and pin 1 of INA134 (or pins 8 and 14 of INA2134) should be connected to audio ground in the receiver.

    (INA134 and INA2134 are higher voltage devices than TPA6132A2, and the receiver may or may not require the higher voltage.  In other respects all these devices are fine for this application.  TPA6132A2 has inherently low on/off pop, and it includes a charge pump to provide a negative supply for its ground-referenced outputs, something that might have to be added for INA134 if it’s not already present in the receiver.)

    Best regards,

    Steve.

     

     

  • 0 in reply to SteveCrump
    Prodigy 20 points

    Hi Steve

    Thanks for the explaination. I'm going go ahead and build with the INA134 so I'll let you know how I get on.

    Regards

    Bob