UCC28951-Q1: Power management forum

vikas salvi

Prodigy 170 points

Other Parts Discussed in Thread: UCC28951, UCC28950

Hi ,

I want to design Isolated dc dc buck converter

Vin = 36V ~ 65V

Vout =14.5 V

Iout = 35A

Desired efficiency > 90% ,

I think of Using UCC 28951 Q1 PSFB , is there any calculator or Quick design guide available ?

please need expert opinion .

thank you ,'

Vikas

over 3 years ago

0 Mike O' over 3 years ago

TI__Guru* 86286 points

Hello Vikas,

There is a Webench design tool for the UCC28951 that you can find at the following link.

https://www.ti.com/product/UCC28951?keyMatch=UCC28951&tisearch=search-everything&usecase=GPN#design-tools-simulation

There is also an application note for the UCC28950 that you can find at the following link. The UCC28951 is a pin for pin replacement for the UCC28950. You may find this information helpful as well.

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

Regards,

0 vikas salvi over 3 years ago in reply to Mike O'

Prodigy 170 points

Hi Mike ,

Thank you for your feedback and sending Design Tool for UCC 28951 .

I have done calculation using the excel tool , but i have below Queries ,

1) i am using Input battery supply 38 ~ 65V dc , the excel tool calculated Cin ( Input cap ) value too high . Is there any other way to calculate CIN in case input source is Battery ?

2) Lout ( Output inductor ) value calculated by Excel tool is almost double in comparison when i calculate Lout value with formula given in Datasheet of UCC 28951 as below

Which is correct formula ? In excel formula frequency is not multiplied by 2 .

3) my application specs are as below ,

Vin = 38~ 65Vdc battery ,

Vout = 14V

Iout = 35V .

Efficiency > 90% ,

Is any other solution available for this isolated dc dc specs ?

Thank you.

+1 Mike O' over 3 years ago in reply to vikas salvi

TI__Guru* 86286 points

Hello,

1. The input capacitance calculation in the tool is for hold up due to having a PFC front end. Since you have a battery and it is not off line the capacitance does not have to be as high. Also the battery is a big capacitor. q = A*t, c = q/V. I think if you go through the numbers your design should have plenty of capacitance. I would still add input capacitance to handle the high frequency RMS currents.

2. There are two frequencies in the design. The primary switching frequency and the secondary switching frequency which is two time the frequency. So that may be why you are off a factor of 2. The excel tool and the application note use the same equation to calculate the output inductance.

3. You can do a high power design with many topologies. The most popular for extremely high power is the phase shifted full bridge controller with ZVS. This helps you achieve greater than 90% efficiency.

Regards,