TLV62085: TLV62085RLTR Generating the audible noise

Hi Andreas,

Is that TLV62085 having the FPWM mode? (If yes then what do we need to change in the hardware) Because the  TPS62826A or the TPS628303 is not footprint-compatible with the TLV62085.

Hi Ankit,

the TLV62085 is automatically changing between PWM and PSM, depending on the load current. But there is no option to force PWM also for light load. If you don't need the full 3A output current, then you could connect an additional permanent load, to move the switching frequency out of the audible range.

But I think the preferable way would be to chose an alternative device with FPWM option. Unfortunately there is no such device, which is footprint compatible to the TLV62085. Let me know if you see any options for changing your design to an alternative device. I would be more than happy to help you with selecting a suitable device.

Best regards,

Andreas.

Hi Andreas,

So there is no other way to stop this audible noise in PSM right? without increasing load.
But i tried with the constant DC load on TLV62085 and it is not generating the audible noise (Even at 100mA) and the waveform at L3 remains the same as the previous one.

It seems the dynamic load (The load current is continuously fluctuating - 50mA) on my PCB is the reason for generating this noise from the TLV62085 To confirm this i increased the inductor value to increase discharger time (470nH to 1.5uH) and i have the clear squarewave on L3, in this case, I am also getting the audible noise.

I increased my load by turning ON multiple LED's but still noise is coming. Below image is the waveform at L3 when i increased my load. (In this case my inductor values is 470nF)

Hi Ankit,

from the last waveform, I believe the audible noise is not coming from the switching frequency. The device is not in PSM for that case. The SW pin signal is looking as expected. I think the noise is generated from the fluctuating load.

What is the frequency of the fluctuating load current?

Is the frequency correlating to the noise?

Where do you observe the audible noise? At the output cap C29 or later in the 3.3V rail?

Is there any additional capacitor later in the 3.3V rail?

How long is the 3.3V trace?

I could review your layout if you want.

You could try to increase the output capacitor C29. 150uF should be no problem.

I would also suggest to try without the Ferrite Bead FB7 (replace with 0 Ohm resistor).

Let me know your feedback.

Best regards,

Andreas.

Hi Andreas,

What is the frequency of the fluctuating load current?

-- I haven't checked the frequency but i do know why my load frequency matters? in general, the load is not in my control the system will take current whenever it's needed.

Is the frequency correlating to the noise?

-- Maybe yes when the sound is at peak same time the current is at peak corresponding to the below image (ZOOM IN Picture of fluctuating load - 50mA)

Where do you observe the audible noise? At the output cap C29 or later in the 3.3V rail?

-- It is coming from the TLV62085 itself.

Is there any additional capacitor later in the 3.3V rail?

-- No

How long is the 3.3V trace?

-- We have a plane of 3.3V.

I could review your layout if you want.

-- Attaching pictures of the layout.

You could try to increase the output capacitor C29. 150uF should be no problem.

-- Tried this after receiving your response but not resolved

I would also suggest to try without the Ferrite Bead FB7 (replace with 0 Ohm resistor).

-- Tried this after receiving your response but not resolved

Let me know your thoughts.

Hi Ankit,

thanks a lot for all the info.

I was asking for the frequency of the noise in order to find the source. If it correlates to the load current then the load might be the source of the noise.

Btw., just to make sure I understand correctly, by noise do you mean voltage noise on the 3.3V output voltage, right? Or do you mean some sound you can hear?

If the noise is a voltage noise on the 3.3V output voltage, could you please provide a waveform of the noise? Could you please also check VIN?

Why do you think the noise is coming from the TLV62085 it self?

Regarding your layout, I think it is pretty much following the reference design, which is good.

The GND path of C31 is pretty long, which is contributing to its ESR. But C31 should not be required as long as C32 is a low ESR ceramic capacitor. This GND path is also forming a loop shape, surrounding the FB signal. I would suggest to remove C31.

The ferrite bead FB7 is placed in one line with the inductor and pretty close to it. Some magnetic coupling may occur. I would suggest to replace it with a 0 Ohm resistor.

The rest of the layout is looking good.

Best regards,

Andreas.

Hi Andreas,

I am talking about the audible noise from the TLV62085 i am not observing any noise in power line. 

In buck converter the inductor is source of the audible noise due to the mutual magnetic attraction between the drum core and the shielded core. (I tried multiple types of inductor - Still the audible noise is coming) That is why i am saying that the TLV62085 is the source.

Let me know if you have any other way to identify the source of  audible noise.

Hello Ankit,

thanks a lot for the clarification. Then this was a fundamental misunderstanding on my side. Sorry for that.

If you already can rule out the inductor as the source of the acoustic noise, then the capacitors could also be the root cause.

Here is an app note related to that topic: https://www.ti.com/lit/ta/ssztb09/ssztb09.pdf

I don't think that the IC would generate acoustic noise.

Please let me know if you also can rule out the capacitors as source of the acoustic noise.

Best regards,

Andreas.