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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

  • Priya,

    Please check using a scope if you see a switching signal on the output pins. The voltage you are seeing is probably an average voltage of the 50% duty cycle PWM which is in phase between the two outputs resulting in 0V differential across the speaker.

    Have you checked the Fault and SD pins?

    I remember your previous post where the EVM had been configured for pre-filter PBTL. Is this a new EVM or the same one from before?

    Regards,

    -Adam
  • Hi Pirya,
    Did you pull PBTL pin to High by opening the connector J13?
  • In reply to Adam Sidelsky:

    Adam/Shawn,
    SD and FAULT pins are measuring 10V. They are pulled to 12V through a 100K resistor.

    I have a replacement EVM with the configuration changes done for me that I am currently using.

    PBTL jumper has been removed.

    I tried probing the OUTL signal with the resistive load connected. I don't see anything but 0V on the scope.
    Same with the OUTR point.

    It makes no difference if I remove the load and keep the load open.

    The resistor does heat up when connected.

    I need to get this demo done. Looking forward to some more pointers.
    Thank you,
    Priya
  • In reply to Priya Nadathur70:

    Priya,

    Please send us a scope image of the output. One probe on each side of the speaker.

    Have you tried using a speaker in place of the resistor to check if there is audio?

    If the resistor is getting hot, there is some current flow through it.

    Regards,

    -Adam
  • In reply to Adam Sidelsky:

    The first picture is the input to the EVM, 1kHz, 490 mV signal. Two waves are seen because one is RINP, 

    the other is the function generator output.

    The loudspeaker when connected gives a loud tone, no clicking/ticking heard like from the past.

    The scope picture however is noisy, only the left part of the speaker shows a switching waveform,

    right part is 0 V (maybe this is how the mono output looks like?)

    I was hoping to snap a perfect EVM output waveform picture.

    Thanks,

    Priya

  • In reply to Priya Nadathur70:

    Priya,

    Do you have your scope grounds connected to the EVM? They should be connected.

    If a tone is heard then the device is operating correctly.

    Regards,

    -Adam
  • In reply to Adam Sidelsky:

    I have all grounds connected to the sleeve of the function generator probe (scope probes, EVM GND).The minute I hook up the loudspeaker, there is a lot of noise seen on the waveforms. I will now run a speech file and see what happens to the amplified sound. Hopefully, there won't be ticking, mangled noises.

    Thanks,
    Priya
  • In reply to Priya Nadathur70:

    Hi Priya,
    This issue is not expected. Could you please help to take a photo of your measurement setup and the EVM config? Where is the input signal from? Could you try with differential input mode and single-ended input mode(close or open J10)?
    Best regards,
    Shawn Zheng
  • In reply to Shawn Zheng:

    For single ended input, is J10 open?
    That may very well be the problem.
    Thanks,
    Priya
  • In reply to Priya Nadathur70:

    Attached are 3 pictures of the test bench setup:

    1. Wavetek function generator provides 1 kHz sine wave input, 490 mV p-p.

    2. EVM shown with input connected to RINP. Note that the PBTL jumper is the only jumper in

    the EVM that is open.

    3. An RCA cable adapter is attached to the function generator probe. One end of this RCA cable is

    used for the input connections, the sleeve of the other end of this cable is used for the GND connections.

    Please review and offer your feedback ASAP. If the configuration needs changing, we need to know right away.

    Thank you,

    Priya

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