TPS54541: Output oscillating

Joshua Kliment1

Part Number: TPS54541

Problem

The output of my TPS54541 design is unstable regardless of load (I didn't push the load above 500 mA in fear of damaging the device)

Specifications
Vin = 24 V	Vout = 5V	Iout = 0 - 5 A

Oscilloscope Screenshots

The following captures are without the Al-electric bulk 100μF output capacitor as I made a mistake in the footprint size (Too small)

[10x probe -> 2V/div / 100ms/div]

No load example - oscillating from ~10V -> ~5V every 300ms

Loaded at 0.5A - oscillating from ~10V -> 5V every 600μs

With the bulk output capacitor inserted (bodged onto the board) the oscillation is still present but the frequency of oscillation is altered (No load - oscillating from ~10V -> ~5V every 800ms)

Design Information

The following is the schematic and layout snippet for the regulator:

I'm guessing it is something compensation related although looking at the recommended design from WEBENCH the compensation scheme is not too dissimilar:

Regarding the layout, I tried to emulate that of the evaluation board.

The following is the BOM for the TPS54541

over 3 years ago

0 Frank De Stasi over 3 years ago

TI__Guru 57555 points

Hello

Your schematic and images did not come through.

However, if the design calls for a 100uF on the output, then you will need to include that.

You can try to "hack" it into the board and see if that helps.

Also, please check your values with the calculator tool on the TI product folder for this device to be sure.

Thanks

0 Joshua Kliment1 over 3 years ago in reply to Frank De Stasi

Prodigy 30 points

Hi Frank,

Thanks for the reply - I've edited the post so that the images are now present.

I have tried with the 100 uF as mentioned (by bodging the component on) and it does change the characteristics but the oscillation remains. In accordance with the datasheet and evaluation board the bulk capacitance isn't always necessary in all applications (the bulk capacitors are no-fit on the eval board for example)

The Power Designer webench recommended calculations are above but I've also used the spreadsheet provided by TI using the component values that I have used. The frequency response from the spreadsheet is given below.