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TPA3245: Sharing differential audio input with D amp and op amp

Part Number: TPA3245
Other Parts Discussed in Thread: OPA1622, TPA3244, OPA1612, OPA1632

Hello,

I have one differential Left/RIght audio input and two audio outputs, TPA3245 for a speaker and OPA1622 for a headphone.

I'm trying to keep the cost down and looking for ways to split the input signals to speakers and headphones without using relay switches, which takes up space and cost.

I first thought shutting down each device when in not use was one way to do it, but I searched the forum and saw that TPA3244(and probably TPA3245) can only be in a sleep mode when the reset pin is low.

If this is the case, I'm thinking the input pins of TPA3245 can effect the OPA1622 signal lines even if there is no power.

Will this connection be possible if I use a load switch to shut down TPA3245 or am I looking at a wrong direction?

  • Hi Brian,

    There's a couple different routes you could go with this. I'm not sure of all of your system requirements but we do have some lower power devices that have a built in headphone lines. What is the voltage, load and power requirements? I'm assuming you wouldn't need to power both the TPA3245 and the OPA1622 at the same time, it's one or the other? 

    When the TPA3245 is in reset mode AVDD is low. AVDD/2 is the DC bias of the input pins. With the DC blocking capacitors, any DC component should be prevented from reaching the OPA1622. 

    Regards,

    Robert Clifton

  • Hello Robert,

    I have a 90W budget to run several devices and I specifically chose TPA3245 for the low THD+N. And also the same for the OPA1622.

    I have 2 inputs that will be connected to these outputs(TPA3245 and OPA1622).

    1. DAC -> OPA1612 -> Outputs

    2. Single-ended input -> OPA1632 -> Outputs.

    Only 1 input and 1 output will be active at a time, so like you have assumed correctly, it's one or the other.

    I have enough MCU GPIOs to shutdown ICs using reset or EN pins.

    For me, the best-case scenario would be to use just the GPIOs to select 1 output.

    2nd best and only option left is to use a relay switch that's around $2.25/1ku.

    Regards,

    Brian

  • Hi Brian,

    90W is too much for the devices with the built in headphone line! 

    The system that you are proposing is likely fine. I would make sure that there's some delay between when the TPA3245 turns on and the OPA1622 turns off and vice versa, to ensure that the devices have proper time to complete startup. 

    Hope this helps!

    Best Regards,

    Robert Clifton

  • Thanks Robert,

    I will try it with the current connection and see how it goes!

    Regards,

    Brian