LM20133: Failure of Power supply circuit (5v to 3.3v)

Abhijith M A

Part Number: LM20133

The damping RC circuit is already in place. But C value is same as C86 and not 5 times. PFB the 5 v generation portion which is used as input to LM20133.

The same 5 v is used to power 3 more modules which are basically relay based I/O modules.

Consider these factors also.

Please suggest some measurement points which can give clue on the stability of the regulator.

I have observed the waveform at pin 8/9 of LM20133 and its appearing as below, is this point of concern. What is the expected output at this point?

over 1 year ago

0 Varun John over 1 year ago

TI__Mastermind 18390 points

Hi Abhijith,

In the attached schematic, I don't find the LM20133. Can you attach the schematic for the LM20133?

Please refer to section 3 of this app note ( https://www.ti.com/lit/an/slva494a/slva494a.pdf ) to measure the SW pin correctly.

The ringing in your picture may be because the device is in a discontinuous operating state. Can you check how the switching looks like first with higher load currents and then with lower load currents?

Best regards,

Varun

0 Abhijith M A over 1 year ago in reply to Varun John

Prodigy 20 points

Hi Varun,

Full scheme is attached for ref.

0 Varun John over 1 year ago in reply to Abhijith M A

TI__Mastermind 18390 points

Hi Abhijith,

Thanks. Please provide the scope shots of VIN, VOUT, SW (with low inductance probe) for light and heavy loads.

It would be good to also check if the compensation network is good enough by measuring the bode plot and checking phase/gain margins.

Best regards,

Varun

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LM20133: Failure of Power supply circuit (5v to 3.3v)