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Enquiry about a LNK304 power supply designed with PI Expert9

Posted by: raimon ribal on

Dear Srs

The power supply is a LNK304 high-side buck-direct feedback topology.
According to AN37, the L value should be higher than 680uH. On the other hand, if we use PI Expert9 the L value is 470uH (see attached files).
So, can we use PI Expert9 result with L value of 470uH?

thank you very much
raimon ribal

Comments

Submitted by PI-Zek on 06/14/2018

Hi Raimon,

Thank you for using our product LinkSwitch-TN.

The result of the PI Expert tool gives the exact inductor value versus the AN-37 which is a design guide for typical design parameters. I noticed in your spreadsheet that you selected a higher device size LNK304. This device size is a bit oversized for a 5V, 63mA design. Toggling to auto-select size (LNK302), it will match the AN-37 suggested value of inductor which is higher than 680uH. It is recommended to use the Auto-selected size in PI Xls. Please see attached file.

The device sizes have different current limit to optimize its operation. The mode of operation is a function of this current limit. This is why they result to different inductor values. I hope this helps.

Also, is your design a buck or a buck-boost? I noticed that you are using a buck-boost spreadsheet for LinkSwitch-TN. In any case, both topologies can be calculated by the PI Expert Online tool to guide you. Thanks.

Attachment Size
LinkSwitch-TN_Buck_LNK302.pdf 460.49 KB