WEBENCH® Tools/TPS54561: Designing a Variable power supply with TPS54561

Hi 

what' s the min possible volage you want to have, as you mentioned, it is very large duty appicatin if you use buck. you can try LM5085 as Pfet Controller, but the efficiency will not be high. 

other topology like Flyback or Forward also can be considered for this application.

Thanks

Hi Daniel,

No matter which topology I go, I am looking at a very long range of output voltage. And it will affect the filter. How can I take care of the output filter?

Can this be solved with a fixed filter and a having a digital pot on the Frequency selection pin so that my switching frequency can adjust itself as per the output voltage and current?

I am Looking for a range of 2V to 48V at 5A.

OR

Can this be achieved with "Digital control of power supply with C2000 MCU's"?

Regards

Vishal

Hi

yes, you can open another ticket and chek the C2000 team. from my side, you can take look at the LM5145 if you can low down the max output voltage from 48V to 45V. It is voltage mode control, so when you fixed Lout and Cout, the LC doule pole is fixed. so the compensation can be also be fixed if upside divide resistor not change.

but LM5145 min off time is 140nS, you can get around 98% duty when you set at 100Khz. which may be not enough for 50Vin to 48Vo with 5A output. I will suggest that you can apply EVM and modified it.

THanks

Hi Daniel,

Thank you for your feedback. Input side, I don't have any limitations. I can use a power supply with 70V input as well. I simulated the design and It works well with 70V input and 48V/5A. I don't wanna go with C2000 digital power design as it will need a lot of development time.

I think LM5145 will solve my problem. Where Can I get more info on adjusting the output voltage while maintaining the stability of my power supply? And if it requires any switching frequency adjustments?

Regards

Vishal

HI Vishal:

I think you can use the excel in below link, and change the low side resistor to see the loop change. in practical way, you need a resistor with external dc souce to adjust the Vo. If you keep high side divide resistor constant, the loop change will be small .

Thanks

Hi Daniel,

I thought of putting a digital pot in the lower resistor position. (100K - 1024 Steps.) But this won't solve my problem fully. As the resolution, I am looking for voltage change is around 20mV (For entire range).

 For that, I should be able to change the resistance in steps of 133m-ohm. Which is not possible with any digital pot. 

Is there any way, I can use a DAC and a microcontroller connected to FB pin to adjust the output voltage?

Regards

Vishal

Hi

yes,  suggest use DAC and a microcontroller connect to FB for output voltage adjusting.

Thanks