PMP21274: Inductor select

Roger Lin

Expert 3370 points

Part Number: PMP21274
Other Parts Discussed in Thread: LM5122, , LMR36015

Tool/software:

Hi team,

My customer is evaluating with LM5122, and they are reference the PMP21274 design

However the inductor is too big, can you please help them simulate the minimum Isat/Irms_max that they needed?

Their Application:

Vin range: 12V~55V

Output: 55Vin

1. 120W output power(Iout 2.18A), minimum Isat/Irms_max

2. 240W output power(Iout 4.36A), minimum Isat/Irms_max

Thanks

12 days ago

0 Markus Zehendner 12 days ago

TI__Intellectual 1795 points

Hi Roger,

LM5122 is a boost controller and PMP21274 is a boost converter reference design. The specification you provided is for a buck converter. Your customer should look into a device like LMR36015 for this specification.

0 Roger Lin 12 days ago in reply to Markus Zehendner

TI__Expert 3370 points

Hi Markus,

Sorry for the typo, their requirement as below

Input: 12V-54Vin

Output: 55Vin

1. 120W output power(Iout 2.18A), minimum Isat/Irms_max

2. 240W output power(Iout 4.36A), minimum Isat/Irms_max

Thanks

+1 Markus Zehendner 11 days ago in reply to Roger Lin

TI__Intellectual 1795 points

Hi Roger,

Using TI Power Stage Designer Tool (https://www.ti.com/powerstage-designer), the currents can be easily computed:

Using a 22uH inductor with 300kHz switching, gives you a peak current of 10.7A and an RMS current of 10A at minimum VIN and full load. So the saturation current should be selected with sufficient margin, especially when using ferrite as a core material.
Using a 10uH inductor with 300kHz switching, gives you a peak current of 21.6A and an RMS current of 20A at minimum VIN and full load. Again, the saturation current should be selected with sufficient margin.

0 Roger Lin 11 days ago in reply to Markus Zehendner

TI__Expert 3370 points

Hi Markus,

Base on your reply, is 10uH inductance over spec in the PMP21274?

Also, can you please help provide the PMP21274 DSN & brd. files for customer circuit build

Thanks

+1 Markus Zehendner 11 days ago in reply to Roger Lin

TI__Intellectual 1795 points

Hi Roger,

For case 2 I would not recommend to use the inductor from PMP21274 as it uses a ferrite core and is close to saturation under steady state conditions already.

For the design files I sent you an email with the link to our internal server.

0 Roger Lin 10 days ago in reply to Markus Zehendner

TI__Expert 3370 points

Hi Markus,

I mean in case 1, since the PMP21274 is 135W 12Vout. You recommend using 22uH, but the reference design only used 10uH

And it is with in the spec that you mentioned

Markus Zehendner said:
Using a 22uH inductor with 300kHz switching, gives you a peak current of 10.7A and an RMS current of 10A at minimum VIN and full load. So the saturation current should be selected with sufficient margin, especially when using ferrite as a core material.

Thanks

+1 Markus Zehendner 7 days ago in reply to Roger Lin

TI__Intellectual 1795 points

Hi Roger,

Using 10uH for case 1 will give you significant inductor ripple between 15Vin and 50Vin. Inductor ripple values will be between 50% and 120% in that range.

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PMP21274: Inductor select