LM5171-Q1: LM5171-Q1

RAYEES K E

Part Number: LM5171-Q1
Other Parts Discussed in Thread: LM5171, LM5032

Tool/software:

I am using LM5171-Q1 device for 2 phase bidirectional boost converter design. In the forward mode the converter will work as Boost and in reverse mode it will work as Buck.

Can you please provide me some reference Design calculation for the 2 phase Bidirectional boost converter using LM5171-Q1 IC.

Mainly I required to refer the output capacitor calculation which includes the ESR requirements for the capacitor.

Thanks, and Regards

Rayees

11 months ago

0 Feng Ji 11 months ago

TI__Mastermind 22650 points

Hi Rayees,

You may find below reference for LM5171.

EVM https://www.ti.com/tool/LM5171EVM-BIDIR

Quickstart calculator https://www.ti.com/tool/download/LM5171-CALC

2 phase boost class H https://www.ti.com/tool/PMP41079

For the output cap, the output ripple voltage and load transient should be considered. Please refer to:

Basic Calculation of a Boost Converter's Power Stage

How to determine bandwidth from the transient-response measurement

Generally, we should use both low ESR ceramic capacitors and bulk capacitors for the output.

Best Regards,

Feng

0 RAYEES K E 11 months ago in reply to Feng Ji

Intellectual 310 points

Hi Feng,

Thank you for sharing the details. I will look into this document.

The basic calculation you have shared will be applicable for normal boost capacitor selection. But for the interleaved it will be different. I have referred the TI reference doc AN-1820 LM5032 Interleaved Boost Converter. Here, i am having one doubt for the output capacitor calculation. For 2 phase boost the RMS current will be very less, and it can be calculated by referring the graph,

but capacitor calculation equation it has mentioned the peak current,

The peak current calculation mentioned in the same document as,

But, the rms current advantage is not reflecting in this equation, can you provide some input on this, what will be the peak current i have consider for this calculation.

Regards

Rayees K.E

0 Feng Ji 11 months ago in reply to RAYEES K E

TI__Mastermind 22650 points

Hi Rayees,

You might have a better insight from below reference on multi-phase application.

https://www.ti.com/seclit/wp/slup323/slup323.pdf

I believe Equation 9 is a rough estimation. And voltage ripple also related to the ceramic capacitors used, layout, ESL of the capacitors and so on. So, I don't think an accuracy equation helps much.

Equation 7 is valid only in CRM as described in the document. The peak current of the inductor in a dual phase design is only half of that of a single-phase design. So, you will get benefit.