Other Parts Discussed in Thread: BQ24072,
Dear people, I am sorry to come with the same questions lots of others have posted.
I was reading all the postings and papers was and trying to find a solution by myself, but without success.
I have built a slightly modified version of the TIDA-00669, using a BQ24072 to also be able to charge the battery via USB
This section works ok, but the BQ51050 refuses to couple with the TX.
The coil, which is recommended in the TIDA-00669-Design is a very small, low inductance coil:
(Wurth Electronics coil part number 760308103206. The inductance is 7.5uh with a 1.55A max current and a DCR of 0.34 Ohms.)
This would fit my needs, but te coupling with the TX does not work with the recomended Series and Parallel Resonant Capacitors.
If I take the suggested value of 183nF for the series cap C1, I deduct an inductance Ls of around 13.84uH. Can this be?
This does not work by me. So I reduced C1 to 68nF and added a bigger magnetic shielding material to the coil.
This helped the TX to see the RX, but the result is a FOD-error.
RECT is also rather low (less then the 7V needed to couple, as I understand.
If I use another coil (Wurth 760308103215), as recomended by Bill Johns in this post: https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1127044/bq51051b-confused-while-selecting-the-coil
and set C1 to be 168nF (calculating with a L1 of 15uH) I get immediately an FOD-error on the TX.
RECT is 2.7 V
The best result I had with the Wurth 760308103204, with an inductance of 16.7 in the datasheet), I set C1 to be 136nF (assuming Ls to be 18.62uH)
By this, RECT shows 9.75V with the coil placed directly on the TX-coil and 7.1V with a 3mm distance from the TX coil.
In the first case, however, the connection (if any) is not stable, the scope showing burst every 2 seconds.
In the second option (with the 3mm spacer), I get inmediately a FOD-error.
I have changed the FOD resistor (200 Ohms) to be 255 Ohm, with RiLim being now 373 Ohms, with the same results.
O am now going to test it with another TX, but since every other receiver I have, Qi compliant or not, succeeds on coupling to the TX, I doubt this is the problem.
Can I please get any suggestions to come out of the misere?
Thank you in advance for your help,
Best regards,
Gustavo
