TPA2039D1: noise issue

attached circuit for check.

Hi Jeff,

Can you provide details on the noise? What kind noise? Is it present all the time or only during audio playback? Scope captures would be helpful.
Having a comparison between input and output signals is also good to know if the source could be the root cause.

Regarding the GND connection, if you have separate grounds, connect the amplifier to AGND. If not having separate grounds you can connect to main GND.

Best regards,
-Ivan Salazar
Applications Engineer

Hi Ivan,

This is input waveform from RD. This noise is always in background, not only happened in audio playback, likes "zi~~~"

And this is SP_OUTLP waveform

Customer reply they have no used output bead 220ohm, only have 680pF bypass capacitor, is it possible cause this noise?

If you need more information please let me know.

Thanks!

Jeff

Hi Jeff,

Please try without the capacitor. Connecting a capacitor directly to the output of a Class-D amplifier is not a good practice as this would cause considerable ringing due to fast switching edges of the modulator, if using capacitors you must add resistors, inductors or ferrite beads before the caps.

In addition, please provide another scope capture of the output but using an LC or RC low-pass filter. This Class-D signal is not telling much about the result at the output of the amplifier.

Could you please try the following, or provide the results if you already did:

• Try to disconnect the amplifier input from the audio source, you can remove the input capacitor or if possible short it to GND. The idea of this test is to know if the noise could be actually coming from a previous stage of the signal path.
• Try to connect GND with some cable close to the supply GND. This is to check if there could be a GND loop causing buzz noise similar to what you hear sometimes from guitar or other instrument amplifiers.
• Inspect the supply voltage, check if the noise could be present at the supply and coupling into the audio path.

Best regards,
-Ivan Salazar
Applications Engineer

Hi Ivan,

We have checked as below.

1. Remove output cap, still have noise.

2. Disconnect input and connect to GND, no noise.

3. Remove the IN+/IN- input cap, but still can find a noise on IN+/IN- pin. please see below waveform.

Thanks!

Jeff

Hi Jeff,

Can you show your connections and how the circuit is modified for each case using a schematic or block diagram? This is just for better understanding.

However since you mentioned that when you disconnect the input audio source and connect the input of the amplifier to GND, then you don't get noise, it would mean that the noise is coming from your audio source. You should check the circuit/device that is connected at the input of the amplifier.

Best regards,
-Ivan Salazar
Applications Engineer

Hi Ivan,

My customer said although input short to GND can avoid noise, but him tried to disconnect input cap as below figure, 

But input side close to TPA2039D still found some ripple on it, and also heard noise.

Is it normally?

Thanks!

Jeff

Hi Ivan,

My customer have also found "bo" sound when TPA2039 enable, I'm asking for EN/IN+/IN-/Vout waveform,

Do you have any idea for this question? thanks!

Jeff

Hi Jeff,

The frequency measurement from each of the captures is different, is there any nearby system/device that could be causing this interference and gets radiated to the amp?.

Regarding "bo" sound, perhaps this is pop noise? Is it something new when changing the passives around the amplifier? Or is it always there? The signal captures will be helpful.
In case it is pop noise, it is usually related to input impedance mismatch, the difference in the capacitors charging/discharging between the input pair causes a transient that is amplified by the device.

Best regards,
-Ivan Salazar
Applications Engineer

Hi Ivan,

My customer provide below waveform when TPA2039 enable.

For the question "any nearby system/device that could be causing this interference and gets radiated to the amp?"

I'm check with my customer will reply later. thanks!

Hi Jeff,

If customer can get captures of both IN+ and IN- they should be able to see the difference between them and that would be the same as the artifact at the output.
For this kind of artifacts they can try adding resistor next to input capacitors to help with capacitor charge/discharge, or also try different AC coupling capacitors to try to make both IN+ and IN- match as much as possible during power up (capacitor values could end up being different).

Best regards,
-Ivan Salazar
Applications Engineer

Hi Ivan,

Do you mean this "bo" sound is caused by IN+/IN- is different?

My customer reply they used single-end input, so  IN+/IN- is different should be normal,

below is  IN+/IN- waveform when enable. Or you have any suggestion for how to modify circuit?

Hi Ivan,

Below circuit is source side.

Hi Ivan,

Add one more question, for continuous "buzz" noise, my customer plan used 5V LDO to solve issue,

if so, how much current is enough for TPA2039 using. thanks!

Hi Jeff,

Regarding current requirements, I'd say 1.5A~2A should be enough, although if they have an estimate of the power, supply (it should be 5V) and load impedance it could help getting a closer estimation.

The observer difference between VIN+ and VIN- is the cause of the pop ("bo"). These signals will be different when using single-ended input, that is correct, and it's also the same reason it is recommended to use differential inputs when possible. Differential input will keep the inputs matching better than single-ended.
As mentioned, in this case what they can do is try different values for the input capacitors and resistors and track the difference between VIN+ and VIN-. the lower the difference the lower the pop noise they'll get at the output.

Best regards,
-Ivan Salazar
Applications Engineer