LM5176: Using the following gate

Donald Ducharme

Part Number: LM5176

Tool/software:

I'm Having problems with the following design:

I'm new at with this product. I used the WEBENCH Power Designer for 12V-30V in and 12V 11A out.

It works fine for 12V power supply I get 12Vout and 4A. However, when I power it with a 24V-28V power supply, I get 5V out. Going back to the 12V power supply I still get 5V out.

The only this I haven't done was "John Wallace 1" suggestion to use 0hm resistors for each gate driver.

I manufactured 10 boards and have lost 6 of them and using them to blink LEDs at 80ms on/off.

I'm using the following MOFSETS: CSD17577Q5AT, CSD17577Q5AT, CSD18514Q5AT, and CSD18534Q5AT.

Is there something I'm missing?

Will the 0hm resistors help?

over 1 year ago

0 Stefan Schauer over 1 year ago

TI__Guru 69561 points

HI Donald,

thank you for using the E2E forum.

Based on the provided data I assume you have large under and/or overshoots on the SWx pins.

If this are violating the abs max ratings of the LM5176 it can lead to the damage you have described.

I am not sure what you mean with "John Wallace 1" suggestion.

But using 0Ohm instead of a PCB wire will make no difference.

Having a 0Ohm on the PCB and replacing this be e.g. 1 - 5 Ohm can make a difference as it will slow down the switching and reduces the ringing due to the parasitic on the board which are generating the above mentioned over and undershoots.

To avoid this following items can be done / can help:

- a good layout

- a good layout (mention this twice as this has the biggest impact)

- gate resistors for the power stage MOSFETs

- snubber on the SWx pins.

If can also be related to instability of the power stage - you can check if you output voltage is stable or has large oscillations.

For both the tests you can start with the 12 V input and slowly increase the input voltage.

The check the signals if there are any waveform not within the expected range - as discussed above.

Best regards,

Stefan

0 Donald Ducharme over 1 year ago in reply to Stefan Schauer

Prodigy 30 points

Hi Stefan,

As I said, I am new and this is my first time attempting this.

1. Should I put a resistor on all four gate drivers or just the HDVR(1/2) or LDVR(1/2).

2. What is a snubber?

I am looking at a duty cycle of 18% with 3 strings of overlapping LEDs at 80ms drawing up 6A 2 times a second.

Thanks.

0 Stefan Schauer over 1 year ago in reply to Donald Ducharme

TI__Guru 69561 points

Hi Donald,

as mentioned first try to capture the waveform on VOUT and SW1 and SW2.

Vout: should be stable and not oscillating - check with a scale of a few switching cycles ( ~20) and a few milli seconds (50 ms e.g. 5ms/div)

SWx: check on rising and falling edges ( scale of your scope needs to be in the lower ns range (e.g. 10ns/div)

Note: here you need to have proper probe setup to avoid noise injection into the ground connection of the scope probe, see

Tip & Barrel:

https://www.ti.com/seclit/ml/slup385/slup385.pdf

Slide 28

For Snubber see:

https://www.ti.com/lit/ta/ssztbc7/ssztbc7.pdf

Best regards,

Stefan

0 Donald Ducharme over 1 year ago in reply to Stefan Schauer

Prodigy 30 points

Hi Stefan,

The "Tip & Barrel" link does not work.

0 Stefan Schauer over 1 year ago in reply to Donald Ducharme

TI__Guru 69561 points

Hi Donald,

can you try again. Just tried and it worked for me.

If not, can you google for slup385.

Best regards,

Stefan

0 Donald Ducharme over 1 year ago in reply to Stefan Schauer

Prodigy 30 points

Hi Stefan,

I'm sorry, even using google I cannot get this document. I login to TI and the browser is stuck on trying "Submit Form".

0 Stefan Schauer over 1 year ago in reply to Donald Ducharme

TI__Guru 69561 points

Hi Donald,

strange, I have attached it here.

7065.slup385.pdf

Best regards,

Stefan

0 Donald Ducharme over 1 year ago in reply to Stefan Schauer

Prodigy 30 points

I'm Sorry,

There must be something wrong with my account as I cannot seem to access this document. When I click on it, a .pdf is downloaded but I cannot open it. Microsoft Edge and Google Chrome get caught in an never ending "Failed to open" loop. And Adobe Reader cannot open it.

0 Stefan Schauer over 1 year ago in reply to Donald Ducharme

TI__Guru 69561 points

Hi Donald,

you are right the attached file above was corrupted. I have updated in - now it should work.

Best regards,

Stefan

0 Donald Ducharme over 1 year ago in reply to Stefan Schauer

Prodigy 30 points

Hi Stefan,

Thank you. I was able to open the document.

0 Brigitte over 1 year ago in reply to Donald Ducharme

TI__Guru 72535 points

Hello Donald,

Thank you for the feedback.

Best regards,
Brigitte

0 Donald Ducharme over 1 year ago in reply to Donald Ducharme

Prodigy 30 points

Hi Stefan,

I put a 3rd party snubber on SW1 and SW2 and U8 on my board burnt out. I stayed with 12V in which gives me 12V out and 5A. Attached is my schematic.

I did not put any resisters on. I am currently building 10 more boards.

0 Stefan Schauer over 1 year ago in reply to Donald Ducharme

TI__Guru 69561 points

Hi Donald,

not sure if I understood your info.

A snubber is an R and a C in series from SWx to GND (or the corresponding supply rail). So if you have used a 3rd party snubber what does that mean.

I understood the U8 got damaged.

At a first point, it would be good to check for the dead time and to exclude a possible shoot through. For that you would need to probe the delay between the gate signals of the two Boost MOSFETs. Probing the SW1 signal in addition would be good as high side gate is HO1 to SW1.

Best regards,

Stefan

0 Donald Ducharme over 1 year ago in reply to Stefan Schauer

Prodigy 30 points

Hi Stefan,

I didn't put the snubber to ground so, everything shorted. I did put the snubber to ground on the next board and got 5V out. I need 12V.

Thanks for you help and understanding. Clearly, still do get it.

Thanks

0 Stefan Schauer over 1 year ago in reply to Donald Ducharme

TI__Guru 69561 points

HI Donald,

really sorry but even after reading your reply several times, I have no idea what info you would like to share or get from me.

May you can help to clarify and help me to understand.

Thanks,

Stefan

+1 Donald Ducharme over 1 year ago in reply to Stefan Schauer

Prodigy 30 points

I Stefan,

I'm moving on to other projects and may come back to this later in the year.

Thank you for your help and understanding.

Don

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LM5176: Using the following gate