Difference between LNK3202D and LNK302D in inductor value

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Dear PI

Currently we are designing a successor product using the LNK3202D. Our previous designed product used the LNK302D, but we thought it would be advisable to use the -TN2 family for new designs
Unfortunately we consider some differences between both designs.
Our topology is a buck topology with 5V output and +/- 20mA output current nominal (60mA peak currents during radio transmissions)

For the LNK302D we could use a much smaller inductor value than for the LNK3202D based on the simulation tool of PI.
Also looking into the application notes (AN-37 and AN-70) we see the following:

- LNK302D - 5V output - buck-> 1200uH inductor value is specified
- LNK3202D - 5V output - buck -> 2000uH inductor value is specified

The problem we encounter now is that for the higher inductor values the magnetic coupling to our on-board power relays (located other side of the PCB above the inductor) is much bigger which gives us much more audible noise
So, my questions is, although we see the LNK3202D as a successor of the LNK302D, why we have to increase the inductor value based on the application notes + simulation tools?

Is it possible to explain us why for the LNK3202D the inductor values are needed to be much higher than the LNK302D, which gives in our design some major disadvantage of having more audible noise?
Why can we not use the same 1200uH for the LNK3202D as for the LNK302D?

In case we don't find a proper solution with the LNK3202D, can we keep using the LNK302D or is this no longer advisable?

Kind regards
Karel

Hi Karel,

Thank you for choosing PI. As for your query, here are the basic difference between LNKTN and LNKTN2

The basic difference between TN and TN2 are the following:

1. The blanking time and minimum on time of both chips are different which constitute to have the variation in the suggested inductance on each device. TN2 will need higher inductance because of higher blanking time and minimum on time.
2. The FET breakdown voltage TN is 700V while TN2 is 725V.
3. And LNK302 has no AR protection unlike LNK3202.

Although LNK-TN is in the product archive, it is still an active product (NOT OBSOLETED)- that means we continue to sell and support them (https://ac-dc.power.com/products/product-archive/linkswitch-tn/), but we don’t recommend for new designs. For new design we recommend using LNK-TN2.

If you have any problems in designing using LNKTN2 or LNKTN2-900 (the latest version of LNKTN) dont hesitate on approaching us. Have a great day ahead!

Regards,

PI-Bucky