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TAS5825P: Reducing idle power draw when connected to only woofers

Part Number: TAS5825P
Other Parts Discussed in Thread: LM5155

Hi!

I'm a part of a project where a TAS5825P is used to drive the woofers of a speaker and we are experiencing fairly high idle power usage (~0.6 W) for only this amplifier (half of total idle power). I was looking at the data sheet and I'm trying to find ways to reduce the idle power draw and noticed that the Quiescent current is reduced from 29.5 to 20.5 mA when increasing the inductance of the LC-filter (page 6, 10 uH to 22 uH).

a. Am I correct in thinking that Quiescent current is causing the idle power draw?

b. Does "No load" here refer to no audio input or no speaker connected?

c. Will increasing the inductance even more reduce idle power further?

d. Will increasing the inductance more have any adverse effects?

Note that the woofers are crossed over at 1.5 kHz, so the amplifiers do not need to output much over 3 kHz.

Is this a path worth exploring? Could we do something else to improve idle power draw?

Some more details:

- 4 Ohm woofers

- 3S1P li-ion battery pack

- Hybrid Modulation

- Hybrid-Pro enabled

- DC-DC booster set to 13-17 V (controlled by Hybrid-Pro)

- Analog gain in TAS5825P set to -4.5 dB

- Digital gain in TAS5825P set to 6 dB

- Maximum (peak) voltage out to woofers is about 14 V

- The unit is silent (no audible hiss from 50 cm distance)

/Anton

  • Hi Anton

    a. Am I correct in thinking that Quiescent current is causing the idle power draw?

       Yes.

    b. Does "No load" here refer to no audio input or no speaker connected?

      It means no speaker connected.

    c. Will increasing the inductance even more reduce idle power further?

      Yes, but when the inductor already large enough, the effect will decrease. You can also try using a smaller C in the filter.

    d. Will increasing the inductance more have any adverse effects?

       Only the cost will be higher, and will take up more space in the PCB. We recommend to use a larger L.

  • Hi and thank you for the quick reply!

    b. Will the result differ with a 4 Ohm speaker connected?

    c. Ok, great. So what would you recommend as a first test in my case? I've attached a picture of the current filter.LC-filter

    Some additional information:

    The DC-DC is a LM5155.

    Battery pack has voltage of 9-12.6 V (empty-full).

    With a lower voltage in to the TAS5825 I assume the losses due to quiescent current will be lower.

    1. Is there a reason to set other limits than 13-17 V for the DC-DC?

    2. Should the analog gain (AGAIN) in TAS5825P be set as low as possible and maximize gain in the separate DSP?

    /Anton

  • Hi Anton

    b. Will the result differ with a 4 Ohm speaker connected?

    Shouldn't change too much.

    c. Ok, great. So what would you recommend as a first test in my case? I've attached a picture of the current filter.

    10uH+680nF seems a good choice, you can also consider 15uH.

    1. Is there a reason to set other limits than 13-17 V for the DC-DC?

    As long as the voltage is within the working range in the datasheet, it all seems fine to us. Use a lower PVDD voltage will surely increase the efficiency and good to final THD.

    2. Should the analog gain (AGAIN) in TAS5825P be set as low as possible and maximize gain in the separate DSP?

    A lower analog gain will benefit for lower channel noise, and the DC offset will also be little lower. We recommend to set it as low as possible.