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TPA6120A2 Series Output Resistor

Sadanori Kato
Guru 36510 points
Other Parts Discussed in Thread: TPA6120A2
Hi,
The internal output devices were damaged when applying the value less than 3Ω@RO at +/- 15V@Vcc and 16Ω@RL to the series output resistor although you recommend that it should be between 10Ω and 100Ω as below. 
So, could you please tell us that cause that you can assume ?
In addition, could you please share the internal equivalent circuit including the internal output devices to us if possible ?
Best regards,
Kato
  • 0
    TI__Guru** 100805 points
    Hi Kato-san,

    Could you share the schematic? Are you applying output series resistor below 3Ohm ?
    This limit in output resistance is specified so that its effect on the load is minimal and to provide the protection necessary against capacitive loads. Also care should be taken in selecting the thermal capacity of the output series resistor, as it will create a potential divider with the load and dissipate power.

    Best regards,
    -Ivan Salazar
    Texas Instruments
  • 0 in reply to Ivan Salazar
    Guru 36510 points
    Hi Ivan-san,
    Thank you for your quick reply.
    The schematic is shown as below although it is same with the schematic which is mentioned in the data sheet except the resistors of RO and RL.
    So, could you please tell me that concern and that cause of the device damage ?
    However, the series output resistors were not damaged by the influence of the heat.
    In addition, could you please tell me the meaning of "the protection necessary against capacitive loads" in detail ?
    Is my understanding correct although I believe that the impedance of the capacitive loads is decreased in the high frequency and the output current is increased ?
    Best regards,
    Kato
  • 0 in reply to Sadanori Kato
    TI__Guru** 100805 points
    Hi Kato-san,

    As D/S says, the output series resistor should be between 10Ohm and 100Ohm, you should better increase this resistance. Probably the damage is being caused by the higher current level the low resistance demands to the amplifier outputs.
    What I meant by protection against capacitive loads is that the device need to be isolated from any capacitance in the output path. This capacitance in the output can be originated from the parasitic capacitance of the circuit board traces and is also be dependent of the length of the cable to the headphones. The amplifier becomes unstable when there is capacitance at its output.

    Best regards,
    -Ivan Salazar
    Texas Instruments
  • 0 in reply to Ivan Salazar
    Guru 36510 points

    Hi Ivan-san,

    Thank you for explaining so politely.
    I understood.
    By the way, could you please share the simple equivalent circuit for TPA6120A2 if possible ?

    Best regards,
    Kato

  • 0 in reply to Sadanori Kato
    TI__Guru** 100805 points
    Hi Kato-san,

    I will see if I can get this equivalent circuit for you.

    Best regards,
    -Ivan Salazar
    Texas Instruments
  • 0 in reply to Ivan Salazar
    Guru 36510 points

    Hi Ivan-san,

    Thank you for your reply.
    I am looking forward to hearing from you soon.

    Best regards,
    Kato

  • 0 in reply to Sadanori Kato
    TI__Guru** 100805 points
    Hi Kato-san,

    Unfortunately there is no equivalent reference circuit.
    Let me know if you have more questions about this TPA6120A2 application.

    Best regards,
    -Ivan Salazar
    Texas Instruments
  • 0 in reply to Ivan Salazar
    Guru 36510 points
    Hi Ivan-san,
    Thank you for your response.
    I understood.
    Best regards,
    Kato