UCC28782: About RDM settings

Kaji@PAN

Part Number: UCC28782

Tool/software:

Hello,
I previously asked a question in the following thread about the problem of startup problems occurring when the RDM constant is set too high.
I would like to continue to question you about this issue.
I received your opinion on RDM settings.
However, I have not been able to find the optimal way to select RDM.
Therefore, I would appreciate it if you could give me some quantitative information.

"Quantitative information" is the following.
Depending on the RDM constants, it may not start.
What RDM constants or related parts, and what constant settings cause it to not start?
Conversely, what settings will prevent startup problems?
Please let me know your opinion.

Best regards,

e2e.ti.com/.../ucc28782-increasing-rdm-resistance-causes-device-to-not-start

over 2 years ago

0 Harish Ramakrishnan5 over 2 years ago

TI__Mastermind 24375 points

Hi Kaji-San,

Thank you for reaching out.

I will check the constraints on the RDM resistor with the design team and get back in a couple of days.

Regards,

Harish

0 Kaji@PAN over 2 years ago in reply to Harish Ramakrishnan5

Mastermind 8080 points

Hello,
Please give me an update on the situation.
Best regards,

+1 Harish Ramakrishnan5 over 1 year ago in reply to Kaji@PAN

TI__Mastermind 24375 points

Hi Kaji-San,

I spoke with the experts and following is the summary of their feedback:

1. An improper RDM along with EMI dithering basically can cause low side MOSFET turn on at higher Vds – so higher power losses can be resulted – which can also have shoot through on either side of the transformer – the worst case can damage the converter.

2. The RDM resistor needs to be highly accurate. It is recommended to use resistor with 1% tolerance.

So it is essential to stick to this value.

Regards,

Harish

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UCC28782: About RDM settings