UCC28951-Q1: DC/DC Converter - Unable to test high loads

Aravind s

Part Number: UCC28951-Q1
Other Parts Discussed in Thread: UCC28951, UCC21530

We are working on designing a DC/DC converter for a 5-kW system using UCC28951 analog controller.

We started with Webench, where the input values were entered, and the schematics generated for the design.
With reference to Webench, PSPICE was used to design the schematic to understand practical waveforms.
In PSPICE tool, TI components for control(UCC28951) and gate switching(UCC21530) were used, and the rest were all ideal components.
It Worked well up to 10A. But after that the output voltage decreases as the load increases.
From the attached image it is understood that the EA- and Comp values saturate, before reaching the output voltage, So the output current also saturates.
In the attached file, the compensation feedback loop was removed to check the output current. But no improvement was noticed in the output voltage.

Please provide your support to resolve the issue as much as possible. This design will be the benchmark for upcoming design like OBC and low kW converters.

over 2 years ago

0 Mike O' over 2 years ago

TI__Guru* 85926 points

Hello,

I am reviewing your inquiry and will get back to you shortly.

Regards,

0 Mike O' over 2 years ago in reply to Mike O'

TI__Guru* 85926 points

Hello,

First you need to check to make sure the UCC28951 and UCC21530 are properly biased and can drive all FETs in the circuit.

Second you need to study the voltage amplifier output, CS and soft start pins to figure out why the design's output drops out after 10 A.

You could be hitting the cycle by cycle current limit and/or hiccup over current protection.

Once you determine why the output is dropping out we can figure out how to resolve the issue from there.

The following link will bring you to an application note that reviews how to design a phase shifted full bridge using the UCC28951. You can use this application to review and double check your design.

https://www.ti.com/lit/pdf/slua560

Regards,

0 Aravind s over 2 years ago in reply to Mike O'

Prodigy 10 points

Dear Mike O'

Thanks for your reply!

For secondary rectification, we use schottky diode instead of MOSFET.

Please share your email address and I will share my design files.

Regards,

Aravind S.

0 Mike O' over 2 years ago in reply to Aravind s

TI__Guru* 85926 points

Hello Aravind,

The e2e is for on line support only. If you need direct support contact you local field applications engineer.

Regards,

0 Aravind s over 2 years ago in reply to Mike O'

Prodigy 10 points

Dear Mike,

Well, I will get back to you after I understand the reason for voltage drop.

0 Mike O' over 2 years ago in reply to Aravind s

TI__Guru* 85926 points

Hello,

Thanks for letting me know.

Regards,

0 Aravind s over 2 years ago in reply to Mike O'

Prodigy 10 points

Hi,

In the design, I simulated and obtained the results using Ideal Mosfet and Diode. But when trying to import object library (.OLB ) in Pspice for TI software it shows error like library not configured. I have attached the image as well. Please check and update me as soon as possible.

0 Mike O' over 2 years ago in reply to Aravind s

TI__Guru* 85926 points

Hello,

I am reviewing your inquiry and will get back to you shorltly.

Regards,

+1 Mike O' over 2 years ago in reply to Mike O'

TI__Guru* 85926 points

Hello,

The free TI PSpice does not allow you to import models into the library. This is most like what your issue is. They have generic FETs and diodes that you can use that will let adjust the parasitic of these components, to match the FETs and diodes your are using.

Regards,

Mike

0 Aravind s over 2 years ago in reply to Mike O'

Prodigy 10 points

Hi,

Thanks for the update.

0 Mike O' over 2 years ago in reply to Aravind s

TI__Guru* 85926 points

Hello,

I was glad to help.

Regards,

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UCC28951-Q1: DC/DC Converter - Unable to test high loads