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TPA3112D1-Q1: TPA3112 shows fault when drive a transformer

Yunjing Wang1
Expert 4720 points

Part Number: TPA3112D1-Q1

Dear team,

My customer is testing our TPA3112, their load is a 1:2 transformer, pull up /SD to VCC.

Set Gain = 20dB, apply a 1Vpp sine signal to input, TPA3112 cannot active regularly. They see fault pin  goes low periodically and output signal shut down periodically, here is the waveform picture of fault pin.

I think may be the short circuit of load causes this issue, when power up TPA3112, the transformer load will be consider as short circuit and cause fault.

What's the work principle of fault detection? why the fault appears periodically?

How can we use TPA3112 to drive a transformer load?

  • 0
    TI__Expert 6295 points

    hello , Yunjing,

        it could be due to periodically OC trigger. Did you connect FAULT pin to SD pin? can you show your schematic?

    regards

    Linda

  • 0 in reply to Xiaolin Qin
    TI__Expert 4720 points

    Hi Linda,

    Thank you for your reply.

    SD pin is connected to fault pin. I will send the schematic to your email, R81 is connected, pull SD pin and fault pin to 5V.

    The issue is mostly comes from transformer load, because the fault will disappear when they connect a resistive load in series on the primary side of the transformer, but customer's application don't allow to add resistive load. 

    So how can TPA3112 drive a transformer load?

  • 0 in reply to Yunjing Wang1
    TI__Mastermind 19860 points

    Hi Yunjing,

    Actually most times, audio amplifiers can not drive transformers directly.

    As you know, the speaker is made up of a series of resistor and inductor, for example, 6ohm+47uH.

    But usually transformer is made up of inductance coil, the inductance is very high.

     

    So on worst case, if input 20Hz sine waveform to the transformer, the impedance of the transformer may be lower than 1ohm. That will lead to OC trigger.

    If customer want to drive transformer, we suggest to add one series resistor on TPA3112 output. But the voltage on transformer will be decreased, they can adjust the Gain setting of TPA3112 to match their requirement.