LM5118: LM5118

Steve Sinn

Part Number: LM5118

I am using the LM5118 in buck / boost configuration with an input voltage range of 8.5-32V & an output of 12V @ a 4A max load. During my testing I have forced the LM5118 into an over current fault and the regulator shuts down as expected. I am having issues with the LM5118 starting back up once the fault is removed. If my input voltage is lower than the 12V output (boost mode) the regulator recovers fine. If my input voltage is higher than the 12V output (buck mode) the regulator will not recover. If I lower the input voltage while in a buck fault the regulator restarts fine. Cycling power on the regulator allows it to recover and run fine. During the fault, Vcc is at 6.9V, the UVLO is 0.25V.

over 5 years ago

0 Garrett Roecker over 5 years ago

TI__Mastermind 21720 points

Hi Steve,

Thanks for reaching out with your question and for using the LM5118. Sorry to hear you are having issues.

Can you please provide the schematic for your application?

-Garrett

0 Steve Sinn over 5 years ago in reply to Garrett Roecker

Intellectual 435 points

LM5118_Base.pdf

0 Garrett Roecker over 5 years ago in reply to Steve Sinn

TI__Mastermind 21720 points

Steve,

Can you please post a higher resolution image of the schematic? I cannot read the component values clearly.

Regarding the test how are you doing the test? I went into the lab and run both and output short tests and overloading test and the LM5118 evaluation module recovered fine.

Thanks,

Garrett

0 Steve Sinn over 5 years ago in reply to Garrett Roecker

Intellectual 435 points

Base.pdf

For my testing, I have both shorted the regulator's output & loaded it with an electronic load to the point of overcurrent.

0 Garrett Roecker over 5 years ago in reply to Steve Sinn

TI__Mastermind 21720 points

Steve,

Is the output current of the design 4A? If that is the case the value of R106 should be 15mOhm. (I used the quick-start calculator). I suggest running through the calculations quickly.

To clarify, when you say the converter doesn't recover, is it at 0V or is the output stuck at some voltage? Can you provide any waveforms?

Thanks,

Garrett

0 Steve Sinn over 5 years ago in reply to Garrett Roecker

Intellectual 435 points

One other bit of information. In the schematic that I attached. R96 = 165K & R102 = 27K. Originally they were R96 = 32.2K & R102 = 5.9K. With the new 165K & 27K the regulator is behaving much better & is restarting as expected. Does this new information shed any light on the underlying issue? I'd like to know what kind of margin I have with these new UVLO resistor values.

0 Garrett Roecker over 5 years ago in reply to Steve Sinn

TI__Mastermind 21720 points

Hi Steve,

Thanks for letting me know that changing the UVLO resistors helped

Per the datasheet, it is recommended to have the top resistor greater than 1000x then VIN maximum. Assuming some tolerance the top resistor this might not be true for you application. For your application I suggest using a resistor greater than 40kOhm to provide some extra margin.

Thanks,

Garrett

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LM5118: LM5118