Suitable Multiphase Controller IC for Buck Converter

Dear Jhun,

Thank you for a quick reply.

I will review the Evaluation Board and will try to create the simulation model of our system using LTC7872 in LTSpiceCAD and LTSpice. I will let you know if I have questions.

Regards.

Dear Jhun,

I have studied the data sheets of LTC7810, LTC7871 and LTC7872. I agree with you that 4 or 6 phases make more sense but it will increase the size of converter as there will 4 or 6 inductors and 8 or 12 Electrolytic Caps. I am more inclined towards LTC7872 as it has 4 phases, so there will 25A per phase.

I have a few questions:

a) I wanted to run some simulations first to get rough efficiency numbers. However, I could not find the models for LTC7872 in both LTSpice and LTPowerCAD. I have updated both the softwares but still this model is missing. Do you know if the models for LTC7872 are available or not ? 

b) How accurate are the efficiency estimation and Closed loop performance of systems designed in LTPowerCAD ? I have designed a 2-phase Buck Converter using LTC7810 in LTPowerCAD and then verified the converter operation in LTSpice. I have attached both the models here. Surprisingly, the power-stage efficiency (including semiconductors, magnetics and capacitors) is higher than 97% at full-load. How close will it be to the actual hardware's efficiency ?

c) Is there a way to limit the inductors currents during the Soft-Start ? Please see the currents in the attached LTSpice simulation file ? The inductor current during steady-state is lower than the current during the Soft-Start. I tried to increase the Soft-Start time, but it did not work. 

d) I can see the simulation model for LTC7871 is available in LTSpice. Can I use only 4 phases in it to imitate LTC7872 ?

Thanks.

LTC7810_Design.zip

Hi Jhun,

Can you please respond to my question ? I am in the process of finalizing the controller IC for my circuit. I want to simulate the converter first to make sure it meets the efficiency and dynamic performance requirements. 

Thanks.

Hello,

Sorry for the delayed response as I was on leave.

zuzahid said:

a) I wanted to run some simulations first to get rough efficiency numbers. However, I could not find the models for LTC7872 in both LTSpice and LTPowerCAD. I have updated both the softwares but still this model is missing. Do you know if the models for LTC7872 are available or not ? 

LTC7872 is not yet available. I would suggest that you use LTC3871 as an alternative for LTPowerCAD calculation as they are the same product family (difference is LTC3871 is two-phase and has integrated driver in the IC). Just design it for 50A (25A per phase still).

zuzahid said:

b) How accurate are the efficiency estimation and Closed loop performance of systems designed in LTPowerCAD ? I have designed a 2-phase Buck Converter using LTC7810 in LTPowerCAD and then verified the converter operation in LTSpice. I have attached both the models here. Surprisingly, the power-stage efficiency (including semiconductors, magnetics and capacitors) is higher than 97% at full-load. How close will it be to the actual hardware's efficiency ?

The efficiency of a buck converter is pretty high. However, all parasitics can't be accounted for but the LTPowerCAD has a good estimate on efficiency.

zuzahid said:

c) Is there a way to limit the inductors currents during the Soft-Start ? Please see the currents in the attached LTSpice simulation file ? The inductor current during steady-state is lower than the current during the Soft-Start. I tried to increase the Soft-Start time, but it did not work. 

Start-up current/soft-start current being higher than the steady-state current is expected and a normal behavior. I don't think that you can mitigate this.

zuzahid said:

d) I can see the simulation model for LTC7871 is available in LTSpice. Can I use only 4 phases in it to imitate LTC7872 ?

Yes you may. The simulation should still work when using 4 phases only. I suggest that you still populate the sns+ and sns- for the unused phases to ensure it will work.

Regards,

Jhun