LM5156H: current amount of inductor

takahiro.yoshida02

Prodigy 20 points

Part Number: LM5156H
Other Parts Discussed in Thread: LM5156EVM-BST

Hi Team,

I have a question about Demoboard LM5156EVM-BST.

now, I try to change the voltage IC with Demoboard LM5156EVM-BST,

testing condition is

>Input voltage 12V,

>Output voltage 25V

>Fsw=2200kHz

>I Out；30mA

then, I modify the testing board as below,

>Inductor 22μH

>Cout =4.7μF×2, and 10μF×2

*FET and Diode is original (not changed to demoboard).

Then, as test result of current measurement.

current amount of Inductor's output is IRMS=182mA, IMAX=231mA (attached)

so, this amount is much larger than calculation result by the below fomula. (calculation result is I MAX=141mA)

please let me know your advice about difference between calculation result and test result.

over 1 year ago

0 Brigitte over 1 year ago

TI__Guru 61025 points

Hello Takahiro,

What did you use as efficiency estimate for the calculation?

Best regards,
Brigitte

0 takahiro.yoshida02 over 1 year ago in reply to Brigitte

Prodigy 20 points

Hello,

estimated efficiency;

efficiency 90% ⇒ IL_MAX=141mA

efficiency 80% ⇒ IL_MAX=150mA

efficiency 70% ⇒ IL_MAX=1460mA

I think, even if efficiency is 70 %, the test reseult is not match to calculation result.

+1 Brigitte over 1 year ago in reply to takahiro.yoshida02

TI__Guru 61025 points

Hello Takahiro,

Most probable, the difference is in your efficiency estimation. If you increase the switching frequency to 2.2MHz but are not optimizing the other components, I expect that the efficiency is not good on the EVM.

Please use the design calculator https://www.ti.com/lit/zip/snvc224 and check if the external components still fit. If you scroll to the end of the calculation, you can see an estimate for the power dissipation you get with this high frequency.

Best regards,
Brigitte

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LM5156H: current amount of inductor