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TPA3136D2EVM: mono load EVM audio demo

Part Number: TPA3136D2EVM

Hi,

I am  working on the audio demo using the TPA 3136D2 EVM. The load is a

PBTL mono load. 

I am using a 4 Ohm 3W resistor for this, resistance measures 4 Ohm on a multimeter. 

This resistor is connected across the OUTL+ and OUTR+ points on the EVM.

 

I have a 1 kHz, 480 mV p-p signal at the RINP TP of the EVM. I can see this on the scope. 

 

I have the voltage between PLIMIT and GND set to 1.25 V.

 

I am powering the EVM at 12V DC.

 

I cannot see anything on the scope when I connect a probe across the resistor ends.

I am unable to read any voltage across the resistor leads as well with a multimeter,

AC or DC.

 

The DC voltage between OUTL+ and GND measures 5.9V DC. Same voltage between

OUTR+ and GND.

 

Can you offer any pointers on this? I have attached the EVM configuration used

for a mono PBTL load. Does this need changing?

 

Thank you,

Best Regards,

 Priya

  • In reply to Priya Nadathur70:

    Priya,

    Your connections can be improved.

    I suggest connecting the function generator signal and ground through one cable using connector J9. You can then observe the signal using a scope connected to TP7/TP8.

    Alligator clips must Not be used for connections to the EVM, they are noisy and unreliable. Test points are not best for input signals, the RCA jack should be used when possible.

    The RCA cable is very long compared to the board traces, this long cable is likely picking up a lot of noise, please connect all grounds to J2 and remove the RCA cable.

    Regards,

    -Adam
  • In reply to Adam Sidelsky:

    Is it likely another EVM needs to be purchased? Are there simple measurements that can be done to verify the EVM is still working? There are a lot of accessories needed to use this EVM, that are only now being bought one at a time. If the EVM is damaged, it is not a very robust product, it seems to damage easily.
    Thank you,
    Priya
  • In reply to Adam Sidelsky:

    Can you suggest a part for the BNC to RCA probe?
    Thank you,
    Priya
  • In reply to Priya Nadathur70:

    Priya,

    I doubt your board is damaged.

    Using a normal BNC Male-to-male cable, use this adapter to convert to RCA:

    https://www.digikey.com/product-detail/en/cinch-connectivity-solutions-aim-cambridge/27-8110/367-1012-ND/385337

    Alternatively you can look up a BNC-male to RCA-male cable.

    Regards,

    -Adam

  • In reply to Adam Sidelsky:

    Adam,
    Thank you for the adapter part information.

    Today, I removed all alligator clips from the EVM and plugged in the RCA cable
    jack into J9. This removed noise from the input waveform.

    I connected the 4 Ohm load resistor across J3 and J8. The power supply voltage drops
    from 12V to 4V when I do this. The power supply reads a 0.4A current draw. Why does this happen,
    what does this mean? The resistor heats up.

    There is a noisy switching waveform that follows the period of the 1 kHz sine input. This again
    is better than before.

    Thank you,
    Best regards,
    Priya
  • In reply to Priya Nadathur70:

    I measured the current drawn by the 12 V powered EVM with no input or load connected.

    The meter reads 40 mA. I am told this should read 400 mA? I am attaching the data sheet

    of the power supply used. Let me know if this needs changing and how.

    Looking at the datasheet for the power supply, the current regulation for a load

    10-90% of rated voltage is <= 100 mA.

    PowerSupply.pdf

  • In reply to Priya Nadathur70:

    Hi Priya,
    Thank you for the update. I think ~40mA current on power supply during idle state on the EVM is expected. When applying the input signal on the device, how much is the input amplitude? How much is the output power? Looks like the power supply has enough current outputing ability, did you limit the output current on the instrument?
    Best regards,
    Shawn Zheng
  • In reply to Shawn Zheng:

    Shawn,
    As posted in the scope picture on this thread, the input is at 490 mV p-p. I had to
    set the function generator at 10 dB attenuation to reduce the input to this voltage
    level.

    When I connect the 4 Ohm, 3W load resistor, I can see the DC supply voltage drop
    from 12V to 4V. I have set PLIMIT voltage to 1.25V DC.

    What is wrong with the given set of information? Please explain why the input
    power supply voltage is dropping.

    Thank you,
    Priya
  • In reply to Priya Nadathur70:

    Hi Priya,
    I don't think there is anything wrong in your EVM setting. Can you confirm there is no current limitation on your power supply instrument? How much is the output current from the power supply in this case? As I explained above, the output voltage from power supply may drop if the output current exceeds the limitation setting. Or can you try with another power supply?
    Best regards,
    Shawn Zheng
  • In reply to Shawn Zheng:

    Shawn,

    Thank you for your reply. I changed the current limiting for the power supply to 1A. 

    Now when I hook the load, the power supply voltage does not fall down to 4V.

    However, I can smell the resistor burning. The scope waveform gets very noisy

    once I turn the power supply on. I am looking for a different power supply to try.

    Why is the load smoking?

    Thanks,

    Best Regards,

    Priya

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