LM51772: Inductor choose

Jeff YANG

Mastermind 7835 points

Part Number: LM51772

vHi,

Due to my customer need support both SPR and EPR using LM51772.

Vin range = 44~52V (nomarlly 48V)

Vout range = 5~48V (need support SPR and EPR)

I using LM51772 excel caculate tool. I found if choose ouput = 5V, the inductor value need very big.

Seem only rising the switching frequency, right? Thanks!

Thanks!

over 1 year ago

0 Bryan Radix over 1 year ago

TI__Expert 3260 points

Hi Jeff,

Thanks for reaching out. Could you please attach the filled out Quickstart Calculator to this thread?

Thank you and best regards,
Bryan

0 Jeff YANG over 1 year ago in reply to Bryan Radix

Mastermind 7835 points

Hi Bryan,

please refer to below.

LM51772_Buck-Boost_Quickstart_Tool_V1_1_0.xlsm

0 Bryan Radix over 1 year ago in reply to Jeff YANG

TI__Expert 3260 points

Hi Jeff,

Thanks for uploading the requested Quickstart Calculator. We'll take a look at it and will get back to you by tomorrow.

Thank you and best regards,
Bryan

+1 Stefan Schauer over 1 year ago in reply to Bryan Radix

TI__Guru 58641 points

HI Jeff,

the tool should assist you finding the right value. Esp. as your output voltage is quite large you need to decide and consider the parameter to fit your requirements. So e.g. with changing the inductor you also influence the efficiency (or losses in the inductor).

So using a lower inductor is still an option. If this goes out of the recommended range the cell will get red an flag this.

Best regards,

Stefan

0 Jeff YANG over 1 year ago in reply to Stefan Schauer

Mastermind 7835 points

Hi Stefan,

If for below application. Do you have suggest inductor value?

Vin range = 44~52V (nomarlly 48V)

Vout range = 5~48V (need support SPR and EPR)

I using Webench tool seem it can choose 1.8uH to 73uH. So using 3.3uH is fine, just impact the delta IL, right?

Another question is I uing webench tool, if input 44~52V, output 48V, seems can't normal generate schematic.

Is the wenbench issue or LM51772 can't support 44~52V to output 48V?

Thanks!

Jeff

0 Stefan Schauer over 1 year ago in reply to Jeff YANG

TI__Guru 58641 points

Hi Jeff,

there is a range for the inductor value to choose and this can be then selected based on the application requirement.

A larger inductor value typically has bigger size, maybe higher cost but less ripple current therefore less core losses.

Based on that factor the selection of the inductor can be done.

The quickstart calculator can help you there with the estimated loss and efficiency calculation.

https://www.ti.com/tool/download/LM51772-QUICKSTART-CALC

Yes, the LM51772 can support input voltage up to 55 V.

The Webench tool seems to have an issue here - will report this to the webench team but the fix might take some time.

Best regards,

Stefan

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LM51772: Inductor choose