LM5022: Inquiries about GaN operation

Hi David,

Thanks for using the e2e forum.
I will review the schematic and check if this issue can be related to the GaN and if a better solution would be fitting for this application.

I will give you an update by tomorrow.

Thanks and best regards,
Niklas

Hi David,

I did not find direct parts similar to LM5022 that a capable of directly driving a GaN.
For now I can recommend the customer to make sure the UCC driver is compatible with the used GaN FET and can supply the gate voltage that is needed.
There also might be alternative GaN FETs that can work with lower gate voltage, which can be driven by such boost controllers directly.

Best regards,
Niklas

Hi Niklas

UCC27512 is also used for circuits now.
I don't think it's a gate voltage problem.
Please check the inquiry below again.

-Questions-

1. At no load, the voltage is 60V output. However, if the load is raised, the voltage drops.

   There is no change in duty even if the load is raised.

  It's their first time using GaN, so is there an error in the circuit configuration?

2. It is said that the reason why they used GaN was because the board had to be made small.

   I would like to introduce GaN as a ti solution.

   If you have a GaN solution that fits the specification above, can you suggest it to me?

Thanks

Hi David,

Thanks for the feedback.
If it is not related to the gate voltage, we need to deeper into the failure itself.

Can you share more information on the voltage drop behavior, when the load increase?
At which load does Vout drop, and is it dropping continuously or with a sharp edge?
It would be great if customer could provide a scope shot, where Vout, Iout and the switch node is visible.

Thanks you very much.
Best regards,
Niklas

Hi Niklas

Thanks for the feedback.

The Vout dropping continuously when the load is raised under no load.

I will ask my customer to let you know about the waveform.

And isn't there a GaN solution of TI with the same capacity? It's a great opportunity to change to TI.

-SPEC-

Input: DC 14~24V

Output: 60V 6A

Thanks

Hi David,

Thanks for the feedback.
I will wait for the customer waveform and check in the meantime, if we can recommend any TI GaN solution.

Best regards,
Niklas

Hi Niklas

My customer says there is no waveform.
Can you guide me on the phenomenon that the output voltage decreases when the load is raised without a waveform?
And please give me a TI solution . I will change it to TI solution this time.

Thanks

Hi David,

Thanks for the feedback.
I have checked our portfolio, but there is not device for this application that can directly drive a GaN FET. Therefore the additional GaN driver is necessary.
(There probably will be parts in the future, but nothing I can suggest to the customer right now)

If they say the output voltage just drops and there is no change in duty cycle, the issue might be related to the system stability.
My assumption would be that the additional delay from the external gate driver affects the regulation loop.

Because of this I was wondering if the output voltage drops instantly or slowly decreases with an increase in load.
A waveform would have been really helpful to understand the device behavior.

Best regards,
Niklas

Hi David, 

A picture of the oscilloscope is enough for us, we do not need a screenshot. We would like to see the CS pin, OUT pin and the gate of the transistor. What is the voltage connected to the VDD of the UCC gate driver? From its datasheet it seems like the max recommended VDD voltage is 18 V. 

Kind regards,
EM