WEBENCH® Tools/TPS54360: TPS54360 inductor noise issue

Hi Jeremy Gu,

Could you please share the below details on this query.?

1. Please share the input/output conditions. VinMin, VoutMax, Vout, Iout, Frequency?

2. Please share the WEBENCH design you are referring to using the ' Share Design' option.

3. Please confirm if you are referring to the SLVU769B EVM design.

4. Kindly share the schematic and results(IL, Vout, Vin) of your modified design for both the load currents(2A & 1A).

Thanks & Regards,

Praveen

Hi Praveen.

1. 52~56 input, 24V output with 3A, frequency is 391.45KHz

2. FYR

https://webench.ti.com/appinfo/webench/scripts/SDP.cgi?ID=6D9E9161919B7256

3. Yes, we are used  SLVU769B EVM and change RLC value for our design

4. Vout is 24V and Vin is 54V for 1A and 2A load

When RT/CLK is 249K ohm, loading with 1A has obviously noise

When RT/CLK is 162K ohm, loading with 2A has obviously noise

Thanks

Hi Jeremy Gu,

We have forwarded your query to the concerned team. We will get back to you shortly.

Thanks & Regards,

Praveen

Jeremy,

Can you please explain what you mean by obviously noise? Please share a waveform so we can help diagnose this issue.

Thanks,

-Sam

Hi Sam,

The inductor has make a sound

Thanks

Jeremy,

Please share waveforms showing SW and VOUT. Audible noise usually means instability.

Does the circuit have noise when operated at a lower output current?

-Sam

Hi Sam,

sorry for late reply

SW voltage is over our scope which can detect

Vout as below picture

with 0 to 2.5A load, inductor noise is not obvious

but Vout is start drop at 2.0A load (23.43V)

2.5A load is 21.48V output

Thanks

Jeremy,

Earlier you said the inductor had audible noise at 1A or 2A depending on switching frequency. Now you say it doesn't have noise up to 2.5A. What has changed in the design?

How are you measuring the switch node? That measurement looks very noisy. Are you using the tip-and-barrel method?

The switch node does look unstable. It should be operating at a constant frequency.

When you say you changed RLC value, do you mean you've updated every component including the compensation network?

-Sam

Jeremy,

I see that VOUT is collapsing. From the waveforms shown over email, VOUT has large ripple with increases with load (~1.2VP-P at 500mAOUT, ~3.2VP-P at 1.5AOUT, and the waveform you showed above at 2.6AOUT.)

Simulations show that the design is stable. This makes me think there may be an issue with the layout. Please share the layout and I will review.

Thanks,

-Sam

Hi Sam,

Jeremy used the TPS65360EVM-182 and replace all the passive components (RLC) on board with their passive components which are suggested in WEBENCH. So layout may not be a problem because they used the EVM board. DO you have any suggestion about the issue?

Roy 

Roy,

You're correct, the EVM has a good layout so your issue is probably not layout related, unless components had to be moved when you changed component values. Let me know if there were any major changes.

Is the IC getting very hot? Does this issue occur at a lower current at a hotter temperature?

Please try lifting one pad of the inductor and adding a loop for a current probe. I'd like to see the inductor current waveform with the switch node.

-Sam

Sam,

The major changes is inductor=68uH and output voltage=24V(feedback resistor). We check the inductor current could support up to 6A. The issue occur at higher output current(2.5A). (inductor has noise at output current higher than 1.5A)

We will check inductor current from switching node.

Regards,

. (inductor has noise at output current higher than 1.5A)

We will check inductor current from switching node.

Regards,

Roy

Roy,

Thank you for that information. Please attach the waveforms of inductor current and switch node when you have them.

-Sam