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I want to built a basic wireless power transmitter at 2.5W (from usb).
I searched and found tida-00415. It looks great and simple, but it's limited to 1W. So, I looked at the tida-00334.
What I'm not understand, is why there is so much differences between those 2 boards, much more parts for the 00334? And why can't we get 2.5W with the 00415 while they both own the bq500212A chip?
I though power limitation was because of the coil caracteristics but I'm not sure.
And I can't find in the bq500212a datasheet, where we choose the output current value?
So, may I use the tida-00415 at 2.5W with minors changes, or do I have to use the tida-00334?
Thank you for your help
edit: I also found the TIDA-00623 for 5W which own 2 ic (bq500511+bq50002) but with no need of tierce parts.
I am wondering wich is the best choice.
The limitations on the different TIDA designs you've investigated, it's the practical power that can be transferred by their respective coils.
The question you have to answer is which coil size meets your needs? That is really for both the TX and RX.
Once you determine the coil size and application size that works best in your application, that my help choose the path for you. The cost of the overall BOM can be a consideration as well.
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In reply to Dick Stacey:
Hi, Thank you for your answer. So it's relly the coil caracteristics which limit the power. I guess differents design it's a kind of optimization evolution over the elapsed time. I would like to use this Wurth coil : katalog.we-online.de/.../760308101220.pdf It's small but It's rated at 1.1A, so it should be ok for 2.5W? thank you
edit: About the current value to set, I guess it's set by the receiver part and not the transmitter part.
In reply to frederic douit:
Sorry, I made a mistake, this coil is for the RX part.
For the TX part, I though about those 2 :
The dcr and inductance seem to be what you said.
I think I will use the tida-00623.
But I can't find coil with the fit inductance.
What have i to change to change the inductance output for using an other coil?
I can't find how the inductance is set.
I can't find where to set the inductance coil.
So I will get a coil that fit with requirement but it's bigger than the RX coil.
I saw that size coils should be almost the same for better performance.
So, with a TX coil of 43mm and a RX coil of 17mm, is it ok or is there too much difference?
Your are correct that the size ratio between the RX and TX is important. The coupling decreases as the RX:TX ration gets smaller.
The coil used on the TIDA-00762 is 760308101103 from Wurth Electronik. It is 6.5uH and 30mm in diameter.
A 43mm coil can work with an RX coil of 17mm, but coupling will be difficult. I have quite successfully worked with a 43mm TX and a 20mm RX. See the TIDA-00318 reference design for an example.
Also, you might find this article helpful. The article on "Designing a Qi-Compliant Receiver Coil" is quite comprehensive.
Thank you for the link, there is a lot of informations.
I think I can finish my design now.
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