LM5176: to drive a GAN switcher @ ~600KHz

Pwr Des.

Part Number: LM5176
Other Parts Discussed in Thread: LM5177

Hi, I would like to use LM5176 to drive a GAN switcher @ ~600KHz.

I have read a reply regarding the same inquiry:

"You can supply an external fixed 5V to VCC by disconnecting the VIN from input line but connecting to VCC. However, your boost strap voltage may also need to be clamped not to exceeding 6V, then you may be okay to drive GaN.

Not sure what GaN do you plan to use. Just note that your GaN may not have a body diode. So you may also need to add external Schottky to allow the inductor current flow during dead time.

So in that case, Vin will be left unconnected? Do you have any example schematic? Also there are many ways to limit the boost strap voltage, any recommended type?

Thanks

over 1 year ago

0 Bryan Radix over 1 year ago

TI__Expert 3260 points

Hi Prw Des,

Thanks for reaching out. I assume you're referring to the post LM5176: LM5176 to drive a GAN switching stage?
As for our advice concerning using an LM5176 in conjunction with GaN switches, we will get back to you by tomorrow.

Thank you and best regards,
Bryan

0 Pwr Des. over 1 year ago in reply to Bryan Radix

Prodigy 10 points

Thank you Bryan, yes that is correct. Waiting your reply. Best regards

0 Bryan Radix over 1 year ago in reply to Bryan Radix

TI__Expert 3260 points

Hi Prw Des,

Once again thanks for reaching out.
Like you're saying, the gate voltage generated by the LM5176 (7.35V) can be too high for a LV GaN device, for this case, a LM5177 could be better suited since it generates a gate voltage of 5V.

Furthermore, GaN-FETs can produce large overshoots and undershoots, which have to be kept under control using auxiliary circuitry.
General advice would be to add footprints to the PCB for:

Gate resistor
Snubbers
Anti-parallel diodes

Regarding example schematics or a reference design, I'm still looking for resources that give examples for ways of connecting the auxiliary circuitry described above.

Thank you and best regards,
Bryan

0 Pwr Des. over 1 year ago in reply to Bryan Radix

Prodigy 10 points

Hi Bryan, Thanks for your time & reply, I will look at the LM5177 , and if you find the example would be a great help!

0 Pwr Des. over 1 year ago in reply to Bryan Radix

Prodigy 10 points

Hi again Bryan, trying to simulate the LM5177 on Webench, having a couple of problems:

1- I am getting a strange error stating the junction temp is lower than ambient.

2- I can change the switching frequency up to 2.2MHz but it is stated 600KHz max in the datasheet.

(screenshot attached)

Please help.

Kind regards

0 Bryan Radix over 1 year ago in reply to Pwr Des.

TI__Expert 3260 points

Hi Pwr,

Thanks for the additional feedback. We will get back to by the beginning of next week.

Thank you and best regards,
Bryan

0 Stefan Schauer over 1 year ago in reply to Bryan Radix

TI__Guru 58471 points

Hi,

I have reported both issues to Webench team but this can take some time to fix.

Meanwhile you can also use the quickstart calculator:

https://www.ti.com/tool/download/SNVR519

Best regards,

Stefan

0 Pwr Des. over 1 year ago in reply to Stefan Schauer

Prodigy 10 points

Thank you Stefan, yes I have been using the calculator instead. when shall I expect for the Webench to be fixed? Shall I click "This resolved my isse" or no?Because I just want to receive a notification once it is fixed. Regards

+1 Stefan Schauer over 1 year ago in reply to Pwr Des.

TI__Guru 58471 points

HI,

this can take several weeks, so far I did not get any time line.

I also can not ensure that this thread get updated once the fix is there - clicking the resolved button will not influence that.

If I get notified about the fix and can try to add a note here but as there is no link between the tools it might get missed - sorry.

Best regards,

Stefan

0 Pwr Des. over 1 year ago in reply to Stefan Schauer

Prodigy 10 points

Thank you Stefan!

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LM5176: to drive a GAN switcher @ ~600KHz