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TPA3116 getting hot in idle

CWilson
Expert 1920 points

Hi,

I've constructed a TPA3116D2DAD PCB and have begun testing. It sounds great, but...:

I'm using Coilcraft MSS1210 10uH (10% sat @ 9.6A, 12mm x 12mmm x 10mm) chokes on the output together with 680nF PHE426 polypropolene caps. BTL mode with BD modulation.

The idle current (ready to play) is (no input signal applied):

48mA @ 12VDC input = 580mW

60mA @ 16VDC input = 970mW

86mA @ 24VDC input = 2W loss

I'm wondering if this is normal? The loss in idle is 2W at 24VDC supply? And the IC and chokes are getting hot (about 50-55C in idle). IC is cooled with small heatsink (2.4 cm x 3.0 cm x 1 mm alu) with 1mm thick gap pad (3W/K).

Without filter, the idle current consumption is about 40mA at 24VDC (within TI spec).

Looking forward to hear some input regarding this issue.

  • 0
    TI__Genius 9175 points
    Hello,

    This seems normal for this device but I will take a look at this and compare with our EVM which uses the same 10uH and .68uF filter values.

    In the meantime can you specify your switching frequency and load impedance?
    In the data above, is the idle current measured with a resistive load or no load?
    This way we can make an apples to apples comparison.

    I would also suggest measuring the inductance of your inductor at the switching frequency you are using. Often times the inductance is rated at 1KHz and may deviate significantly in the 400KHz - 1.2MHz rage.

    Best Regards,
    Matt
  • 0 in reply to Matthew Beardsworth
    Expert 1920 points
    Hi Matt,

    Thank you for your input. Regarding your questions:
    1) fsw is 400kHz (AM0, AM1, AM2 = GND).
    2) No load (open connectors). As I recall, it's about the same with 4R speakers connected.
    3) Inductance of the power inductor MSS1210 is specified at 100kHz 0.1Vrms. Coilcrafts measurements states 10uH from 100kHz and beyond 4MHz (unknown current). The DCR is only max. 16mOhm. Datasheet for inductor: www.farnell.com/.../1681953.pdf . It contains a graph of the frequency vs. inductance on page 2.

    Q1) What is the reason for the higher loss in the TPA3116 at 24V compared with 12V? Is it the internal power consumption and an internal linear regulator from 24V instead of 12V?
    Q2) My sync pin is floating since I'm not using it. Is that OK?

    Best regards,
    Casper.
  • 0 in reply to CWilson
    TI__Genius 9175 points

    Casper,

    1. With our EVM I measured 40mA at 12V and 65mA at 24V 400KHz. The idle current increases with supply voltage due to losses in the output filter. The PWM output amplitude is equal to the PVCC supply voltage. With higher voltage the loss in the output filter also increases.

    The discrepancy between the EVM idle losses and your measurements is based on the component properties of the LC filter (DCR, inductance at the switching frequency, capacitor ESR etc).

    2. the Sync Pin can be left floating without any issues.

    Best Regards,

    Matt

  • 0 in reply to Matthew Beardsworth
    Expert 1920 points
    Hi Matt,

    OK thank you.
    The performance of the inductors should be good, but of course if there is a circulating current in idle, there will be losses in the filter.

    Q) Do you know the current when the inductance is 10uH and the voltage is 24VDC and fsw = 400kHz?
    Q) Do you estimate the loss to be much smaller if I use a higher switching frequency for the IC due to smaller ripple? (only in idle of course).

    Also I'm using a small LP2950CZ-5.0 regulator to some LEDs (2mA/LED) and for the level of my input signals (SD, FAULTZ, MUTE etc.) instead of pulling them to AVCC.

    Kind regards,
    Casper
  • 0 in reply to CWilson
    TI__Genius 9175 points
    Hi Casper,

    1. I do not know the current circulating in the filter loop. To get an estimate you can try simulating the filter using a SPICE tool such as TI's TINA. If you simulate one leg of the output rather than the full bridge, the load should be 1/2 of the nominal load used.
    http://www.ti.com/tool/TINA-TI

    2. You may notice less idle losses higher switching frequencies but since the gate drive is working faster, gate drive losses increase due to slewing the output FETs which may counteract this.

    3. You can try shifting the cutoff frequency in a little bit closer to the 20KHz audio band to get better rejection at the switching frequency. This may also help reduce idle current loss in the filter.

    Best Regards,
    Matt