TPS54360: TPS54360

Raja Ahmed Bilal

Part Number: TPS54360

Hi!

I have designed the power supply +5V using TPS54360.

The issue I am having is that resistors for regulating the output voltage R1 and R2 shown in figure below have problem. I am using a potentiometer to regulate the output voltage. At the moment R1 is 51k and R2 is 8.7K.
When i turn on the power supply and connect it to load then i hear the noise from potentiometer.

If i change the impedance then at some point I dont hear any noise but when i connect the load then again it starts making noise. Is it something related to power rating? Normally this feedback path should not consume too much current?

over 7 years ago

0 Samuel Jaffe over 7 years ago

TI__Mastermind 25590 points

Raja,

That's an interesting issue! You're right, you should see around 100uA going through the POT which isn't much.

1. What does the noise sound like? Is it a single tone? A few tones? Or is it like noise?
2. Do you see any subharmonic oscillation on the switch node?
3. Do you see resonance between L1, C2, C4, L5?

-Sam

0 Raja Ahmed Bilal over 7 years ago in reply to Samuel Jaffe

Prodigy 210 points

Hi!

I had issue with the capacitors at the output. I was using ceramic caps and it seems that they were not the right type.
But now I have another issue which is that output is +5V when there is no load at output but as soon as I connect the load it drop to 2.5V, I have external RC filter connected as seen in schematic.
I am unable to track the issue for this problem.

0 Samuel Jaffe over 7 years ago in reply to Raja Ahmed Bilal

TI__Mastermind 25590 points

Raja,

Okay, let's get the circuit running, then see if the pot noise issue persists.

Please fill in your specs and we'll go from there:

VIN = ___
VOUT = 5V
IOUT = ___

What is the purpose of L2 and L5? (They can help filtering but they can also break the circuit if not done carefully)
What tools did you use to select components in your schematic?

-Sam

0 Raja Ahmed Bilal over 7 years ago in reply to Samuel Jaffe

Prodigy 210 points

VIN = 18V
VOUT = 5V
IOUT = 100mA

L5 is placed on board.
L2 is used for filtering.
I used Wirebench for simulation.

0 Samuel Jaffe over 7 years ago in reply to Raja Ahmed Bilal

TI__Mastermind 25590 points

Raja,

Are L5 and L2 absolutely necessary for your design? Try replacing them with 0-ohm resistors and see if that helps operation.

What did you mean by the ceramic caps were the wrong type? Usually we like a little bit of ESR on the output cap to dampen any ringing/resonance with the inductor, which is why WEBENCH suggests an electrolytic cap on the output. That may also be causing issues if you're seeing ringing/resonance on either side of L5.

Is 100mA your max IOUT? Your inductor (as well as the IC) are sized for several amps.

-Sam

0 Raja Ahmed Bilal over 7 years ago in reply to Samuel Jaffe

Prodigy 210 points

Yes, I know IC is sized for 3.5A, but the load requirement for this design is around 100mA. Also I removed the L2 and L5 and replaced with 0 ohm but still the problem is same.

0 Samuel Jaffe over 7 years ago in reply to Raja Ahmed Bilal

TI__Mastermind 25590 points

Raja,

Okay, we're narrowing down the issue.

Can you share a scope shot of VIN, SW, FB, and COMP at No Load, Full Load, and the transition?

-Sam

0 Raja Ahmed Bilal over 7 years ago in reply to Samuel Jaffe

Prodigy 210 points

should i set the trigger on one signal and share the scope shot or?

0 Samuel Jaffe over 7 years ago in reply to Raja Ahmed Bilal

TI__Mastermind 25590 points

Raja,

Trigger on rising SW for the No Load and Full Load (and zoom in so we can see ~5 SW cycles).

Trigger on VOUT falling on the transition (and zoom out so we can see the whole transition).

I've been running simulations and it seems okay. I'll keep looking into this while you take those shots.

-Sam

0 Raja Ahmed Bilal over 7 years ago in reply to Samuel Jaffe

Prodigy 210 points

Full load SW trigger.

No load SW Trigger

Vout transition at full load. Green is Vout.

0 Raja Ahmed Bilal over 7 years ago in reply to Raja Ahmed Bilal

Prodigy 210 points

0 Raja Ahmed Bilal over 7 years ago in reply to Raja Ahmed Bilal

Prodigy 210 points

No load is connected and Vout is Green.

Vout with full load, Green is output.

0 Samuel Jaffe over 7 years ago in reply to Raja Ahmed Bilal

TI__Mastermind 25590 points

Raja,

Thanks for the waveforms. What are each of the traces?
Green is VOUT
Pink is VIN?
Yellow is SW?
Blue is COMP?

Can you check to make sure FB follows VOUT as expected?

-Sam

0 Raja Ahmed Bilal over 7 years ago in reply to Samuel Jaffe

Prodigy 210 points

Hi!

I am about to leave office now. I will do the measurements tomorrow and will come back to you. In meantime if you let me know about the exact test plan which I should do, I will appreciate it. And yes the signals are like this,

0 Raja Ahmed Bilal over 7 years ago in reply to Raja Ahmed Bilal

Prodigy 210 points

Did you find any solution to this?

0 Samuel Jaffe over 7 years ago in reply to Raja Ahmed Bilal

TI__Mastermind 25590 points

Raja,

I'm talking with a coworker for his opinion. He should get back to you soon.

-Sam

0 Ambreesh Tripathi over 7 years ago in reply to Raja Ahmed Bilal

TI__Expert 6860 points

Raja ,

Can you please share the Layout of your design .?

Here are the critical points that needs to be followed on the layout .

If you dont have a good layout of the board , then i would recommend to order one evaluation module from ti.com which is already configured for 5V output .

---Ambreesh

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TPS54360: TPS54360