LM3150: LM3150 not regulating

Joel Findley

Part Number: LM3150

I'm trying to have a 3.3V 9A (very similar to eval board) with an air core inductor and I'm having an issue with keeping regulation, I had to remove my Cff cap in order to get the output to the proper voltage, with this cap populated I was at 4.0V not 3.3V. I then realized that the Ilim value was too low and recalculated with my current FET Rds_On and now my 3.3V regulator is working from open load to 9A as designed without issue. I however also have a 12V 2.5A regulator that i can't get to regulate, I've removed the Cff and it sits at 11.9V until I i put a 1A load on then it starts to lower the output voltage, the switching waveform looks clean i'm at 330kHz, Design was targeting 300kHz. If i remove an output cap to get closed to my minimum calculated value the output voltage rises. Any help will be great.

over 6 years ago

0 David Baba over 6 years ago

TI__Mastermind 26350 points

Hello Joel,

Can you share your schematic please?

Thanks.

David.

0 Joel Findley over 6 years ago in reply to David Baba

Prodigy 100 points

Here is the requested schematic, I've changed the High side gate FET from 0 Ohm to 10 Ohm and that helped the controller regulate when I had a zero ohm the FET was ringing and the Switch node wasn't close to normal, but the output still drops from 12V at 500mA to 11.7V at 1.5A,

0 David Baba over 6 years ago in reply to Joel Findley

TI__Mastermind 26350 points

Hello Joel,

Glad you are making some progress. Where are you measuring Vout? Would need to measure at the point of the top feedback resistor as this is what the converter is regulating.

Is the switch node Stable in both cases of Iout?

Thanks.

David.

0 Joel Findley over 6 years ago in reply to David Baba

Prodigy 100 points

I'm measuring at the point you specify, the switch no is stable at both cases i'm at measure 320kHz open load and 333kHz at 1.5A.

0 David Baba over 6 years ago in reply to Joel Findley

TI__Mastermind 26350 points

Hello Joel,

Does the vout drop suddenly as the load increases and approaches 1.5A? Or does it drop gradually/linearly from the range from 500mA to 1.5A?

Can you measure the Feedback voltage + ripple voltage on the switch node in both cases (500mA/1.5A)?

Thanks.

David.

0 Joel Findley over 6 years ago in reply to David Baba

Prodigy 100 points

It seems to gradually increase, however I went back and measured directly at the top of the FB divider and this point seems to be regulating without issue, I'm at 12.05V @ 0A and 11.99V @2.3A , it looks like from the the output regulator, through the copper of the PCB to my output harness and then to the load i'm getting a voltage drop and I was regulating properly this entire time.

0 David Baba over 6 years ago in reply to Joel Findley

TI__Mastermind 26350 points

Thanks for Varying, looks like the converter is doing what its supposed to do, looks like thickening up the copper of the current carrying path will help greatly.

Hope this helps?

David,

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LM3150: LM3150 not regulating