LM5155: These is big difference of efficiency between the actual data and result of Quick Start Calculator.

Hello Kazuya, 

Thanks for reaching out. Let me share here some comments with you:

• The Excel calculator is just a tool to give you an estimation of the efficiency, but the this must always be measured and optimized in the lab. I would recommend to check the lab setup as well (e.g. the use of 4 wire connection and 4 multimeters to have accurate reading of Vin, Vout, Iin, Iout to perform the efficiency measurements).
• The chosen inductor has a series resistance that is much higher than the original inductor on the EVM 
• I see that the max load is 80mA, is that correct? Maybe a design in DCM with a smaller inductor might also be a solution in this case. Other than this, the customer might consider to lower a bit more the frequency too. 
• As the chosen diode is a super fast recovery one, I would not be too much concerned about its Qrr.
• Additional comments: I see that currently the sense resistor is set so that the actual switch peak current limit is 10A, I would suggest to lower this peak current value, also because it seems like the inductor chosen by the customer is saturating at 1.7A. Other than this it looks like the phase margin is a bit low as the C_hf capacitor is significantly bigger than the suggested one, I would recommend to lower this values.

Please let me know if I can help you furthermore. 

Kind regards, 

EM

Hello EM,

Thank you very much for your reply.

I will check the customer efficiency measurement environment whether it is similar with the best environment you said or not.

Could I ask you several additional questions?

Q1. Does this calculator have a field for entering the DCR of inductor?

Q2. If Q1 answer is no, is their any way to reflect RDC parameter of inductor in the efficiency calculation?

Q3. Are only MOSFET parameters and Diode parameters used for the efficiency calculation?

Thank you again and best regards,

Kazuya.

Hello Kazuya, 

Thanks for your feedback. The calculator does not have a field to enter the DCR of the inductor, but you can calculate the power dissipated on the DCR in this way: R_dc * I^2 = Ploss , where R_dc is the DCR resistance of your inductor and I is the rms value of the current in the inductor, in this way you obtain the power loss on the DCR of the inductor. About your third question: I cannot unlock this Excel file unfortunately, but please keep in mind that in general efficiency is not only affected by diode and FET but also many other parameters (e.g. layout, switching frequency, lab setup etc.) . You might want to take a look at page 28 of the datasheet to see an example of the efficiency estimation for a boost (but most of these info apply to a SEPIC too). 

Kind regards, 

EM