UCC256403: Questions on UCC256403 LLC Design for 48V Battery Charger

Hi, 

Please find my explanation below:

1. Your approach is not correct. You should put roughly 150% as ηOVP and adjust auxiliary circuits according to it. 

What you need to do is that:

You should create 2 excel sheets, one is with output of 48V and another is with output of 58.7V and then use same magnetics in both the design calculator. Then you check and adjust the values of all the components of the pins that will satisfy both the excel sheets and all the values have to be designed according to the worst case scenerio.

2. kBMT option is BMTL/BMTH ratio. By this programming, you can program BMTL and BMTH values, and to know how burst mode works with these 2 values,  you can refer section 7.4.3 of the datasheet.

3. You can check sections 1.11 of FAQ document (https://www.ti.com/lit/an/sluaal2/sluaal2.pdf?ts=1758010292811&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FUCC256404) for compensator design.

Regards,

Sougata

Hello Sougata,

Thank you very much for your reply.

To confirm my understanding: are you suggesting that I should set ηOVP to 150% and adjust the charging voltage through the feedback circuit? If so, does this mean that the OVP function itself will not be used? A voltage of 72 V would be too high for the battery.

Also, regarding your suggestion to create Excel sheets for both 48 V and 58.7 V, could you please clarify what specific “worst-case scenario” conditions should be assumed when designing all the values?

For implementing CC/CV, I am currently referring to Section 1.13 of the FAQ document (www.ti.com/.../sluaal2.pdf), and my reference design is PMP40766 (www.ti.com/.../PMP40766).

Regards,

Hi,

I wanted to say that keep ηOVP in such a way at the voltage where you want to protect your auxiliary circuit (not feedback circuit) and battery. Suppose, you have all the components that can take up to 100V in Aux circuit rail and your battery at the output can take upto 70V, then you should put ηOVP as 60V to protect the circuit. 

So, for worst case scenarios will be coming with highest switching frequency (Mmin at Voutmin and Vinmax) as well as lowest switching frequency (Mmax at Voutmax and Vinmin).

If you are using op-amps in your CC-CV ref design, you can look into the following document to refer compensator design:

https://www.ti.com/lit/an/slva662/slva662.pdf?ts=1758188390193&ref_url=https%253A%252F%252Fwww.google.com%252F

Regards,

Sougata

Hello Sougata,

Thank you for your kind explanation.

To summarize your response, my understanding is that ηOVP should be set at a voltage level that the battery (or auxiliary circuits) can safely withstand, and the design should ensure stable operation across the expected Vin and Vout range.

I will study the documents you shared in more detail.

Regards,