TPSM5601R5HE: incorrect regulation

Hello,

Please provide the schematic and layout.

Best regards,

Ridge

I can provide schematic for now, unfortunately I cannot provide snippets easily (due to legal reasons)

Hello,

Can you show the measurement setup?

We also need to review the layout if it is possible.

Can you provide waveforms for Vout, Vin, and the SW node?

Best regards,

Ridge

I will add some screenshot and snippets, keep in mind I modified this board with some resistor values that generate my desired output (but they are not the tabular one)

1.8 VOUT

3.3 VOUT

5V0 VIN

SW PIN (both regulators)

closeup of layout

Hello,

Please show the entire layout for the device.

Also, the SW node looks very unstable. What is the part number of the input and output capacitors? The output capacitance could be de-rating.

Best regards,

Ridge

OUT: GCJ32ER70J476ME01L
IN: C0805X475M3RACAUTO

I am checking what's my ability to share design details in the meantime.
I am comparing the layout to the one in the datasheet, placement is quite similar obviously. Although there is less copper area on the external layer in general compared to the example. All nets are well connected to a wider plane on the adjacent layer 

Hi Alessandro,

Ridge is OOO and will reply on Monday.

Thanks,
Andrew

Hello, 

You can also share the layout with us via private message if that works.

You will need more output capacitance for this design to be stable.

Is you look at Figure 8-2 in the datasheet, you will see a curve of minimum effective output capacitance for given output voltages.

3.3V requires more than 80uF and the part number you shared de-rates about 25% under 3.3V bias.

1.8V requires more than 150uF of effective capacitance.

Please add more capacitance to the board, with the datasheet recommended feedback dividers, and retest.

Best regards,

Ridge

Sure I will test and I will let you know, I can share with you directly more details of the layout as well, thanks

Anyway I have 2 parallel capacitors on the output so effective capacitance is about 90u, 3.3V under that assumption should work

Hello,

I checked the manufacturer de-rating curve from the part number provided for Cout and it looks like this:

So the 90uF is derating to about 67uF when biased with 3.3V. I recommend retesting with an additional capacitor or changing to a higher voltage rating with a softer de-rating profile.

I will reach out via private message for the layout.

Best regards,

Ridge 

Sorry for late reply, I had to order the caps and they just arrived.
I tried doubling the output capacitance but I saw no improvement unfortunately

Hello,

are you able to share the layout with us vis private message?

Best regards,

Ridge

I did it now, thanks!

Replied via private message