TPS54291: Non-monotonic power supply problem

Filipa Bobinac

Part Number: TPS54291

Hi,

I have problems with non-monotonic power supply on the left side of the circuit (1.8V @ 1.5A) while the other side (3.3V @ 2.5A) is okay. You can view the schematic on the first picture.
Non-monotonic power supply can be seen on the second picture, marked with yellow color. When something occurs, TPS54291 stops switching (same picture, pink color) and Vout drops and then turns on again.

I've calculated component values (Lmin ~ 5.7 uH) and chose 8.2uH for which the minimum capacitor value is ~22.78uF where I took actual value of 22uF. I've also tried with 6uH and 22uF.
I've summed up total capacitance on the 1.8V trail and it is below the maximum. We assume that maybe overcurrent is detected, but we're not sure. Do you think maybe something else is happening?

Regards,
Filipa Bobinac

I

over 4 years ago

0 JohnTucker over 4 years ago

TI__Guru**** 191445 points

Filipa,

It looks like you are experiencing over current with hiccup restart. Can you measure the inductor current to be certain?

0 JohnTucker over 4 years ago in reply to JohnTucker

TI__Guru**** 191445 points

Filipa,

Do you have any update?

0 Filipa Bobinac over 4 years ago in reply to JohnTucker

Prodigy 40 points

Hi John,
I'm so sorry for slow response.

The current through the inductor is approximately 700 mA. We've put 10 mOhm in series with inductor and the voltage drop was about 7.1 mV.
Spikes on the picture are result of switching effect, is it possible maybe these spikes can cause over current? We tried changing the snubber circuit and placed 940 pF and 5 Ohm values but nothing happened.

Thank you for your help,
Filipa

0 Anthony F over 4 years ago in reply to Filipa Bobinac

TI__Mastermind 35115 points

Hi Filipa,

Based on this measurement it does look like this is likely not related to an overload on the output.

When you see this issue on the 1.8V output, do you also see switching stop at SW2? When hiccup is triggered in the TPS54291, both PWM outputs should be disabled.

Also have you verified the EN1 voltage is not glitching?

Best Regards,
Anthony

0 Filipa Bobinac over 4 years ago in reply to Anthony F

Prodigy 40 points

Hi Anthony,

It doesn't stop switching at SW2.
EN1 is high and the output is disabled when this issue occure, so obviously our power controller is programmed wrongly.
Many thanks!!

Best Regards,
Filipa

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TPS54291: Non-monotonic power supply problem