BQ51013B capacitors values

Please use the below spreadsheet to calculate those two values. You will need to measure the coil inductance value by itself (Ls) and also the coil inductance value with the TX under it (Ls'). Plugin those values the spreadsheet formula and it will tell you the correct value for C19 and C21.
www.ti.com/.../sluc566

Thanks,
Wenjia

Also, the FOD circuit doesn't look correct. You will need to have a Ros resistor connected between RECT and FOD pins. Also you need a resistor from ILIM to FOD. Please refer to bq51013B datasheet for recommended application circuit. If you are not going to use the FOD function, you can use the same value as in below EVM.

http://www.ti.com/lit/ug/sluua44a/sluua44a.pdf  

If you want to tune FOD with your system, the below tool can help you with it. There is a detailed manual inside the tool.

http://www.ti.com/lit/zip/sluc577   

Plus, the 7.5k ILIM resistor will only give you ~30mA ILIM.

Thanks,

Wenjia

Hi Wenjia,

Thanks for answers. I calculated 238nF and 3.4nF and put that. Should that work even if I didn't correct FOD circuit for now?

Best regards,
Darko

Darko,

Even if you don't use FOD, you still need to have the resistors connected to the right pins. You can start with the value on our EVM.

Thanks,

Wenjia

Hi Wenjia,

OK thanks, just wanted to know do I need to change resistors also for begin. I calculated 238nF and 3.4nF for 13uH coil, and thought that may be should detect without pins change. But ok will arrange resistors connections also.

Best regards,
Darko

I made changes, capacitors 200nF and 2nF and resistors connected to appropriate pins but nothing. Do you think coil is ok? What kind of signal I should have on coil.

Darko

Hi Wenjia,

I used Wurth coil 760308101208, it is 10mm diameter. Do you have experience with that may be it is problem, cause small, but they said wireless charging coil.

Best regards,
Darko

Can you draw me the updated schematic so I can check again if you resistor connection is correct?

We have used he 10mm diameter coil in our low power wireless design and it worked well. Please refer to below
www.ti.com/.../TIDA-00318

Similarly, for different coils, you need to calculate the Cs and Cd again.

Thanks,
Wenjia

Here is schematic with changes. Coil is Wurth original. Values of Cs and Cd are according to Excel calculator. But nothing.

Darko

What is the TX you are using? Can you send me the waveform of RECT and OUT pins during start up?

Thanks,
Wenjia

I am using China made unit for TX based on ST chip. It has antenna about 50mm round inside. I can make you and send, only on that 2 pins?

Darko

If you have enough probe, the signal on COMM and AC1 will also be helpful.

Please note that with 10mm coil at RX and 50mm coil in TX, you will likely have coupling issue as the physical size of the two coils are too different. Try to add a bigger shielding to your Wurth coil.

Thanks,
Wenjia