Wireless Receiver Not Providing Output Power

Crawford,

The 9.5mm coil is not large enough to get the correct coupling with the Qi transmitter.  I suggest you start with a standard coil, possibly one recommended in table 7 in the bq51013B datasheet.  Use that to debug your system then you can start looking at smaller coils.

I would suggest that C37 be composed of 3 separate capacitors.  All of the current must pass through these capacitors and using 1 generally leads to too much heating and poor results.  Most applications also use 2 capacitors for C39 to get the correct calculated value.

What current do you plan to use for this system?  The ILIM resistance is set for 1.2A.  That would mean your nominal maximum current is 1A, or 5W.  That would definitely overpower the small 9.5mm coil.

The TS/CTRL pin is a temperature sensor.  If you do not want to use that function, it must be tied to ground with a 10kOhm resistor.

Regards,

Dick

To add a little more info to Dick's very good reply.

We have a TX trouble shooting guide in FAQ section and slide 6 describes the start up sequence, below link.  Due to the low coupling factor with a 9.5mm coil you are probably not generating a voltage at RECT greater than UVLO.

https://e2e.ti.com/support/power_management/wireless_power/w/wireless_power_faq

More info on coils can be found in the below article.

http://www.ti.com/lit/ml/slyt570/slyt570.pdf

Also see TI wireless power web site for a more complete list of presentations and articles.

www.ti.com/bqTESLA

Gentlemen,

Thank you for your replies. Dick, we are expecting 500mA or less. Does that mean that R11 should be changed? Also, I know you said that this antenna may be too small. When we ran the numbers to calculate the quality factor from the datasheet, we came up with 95 which is greater than the 77 requirement. Is that cutting it too close?

Best,
Crawford

Bill,

I took a look at RECT (pin 18) on our board and it seems to be at ~500mV. UVLO on on the datasheet seems to say that typically UVLO is 2.7V but that depends on the condition of VRECT. Since the two voltages seem coupled, what is your impression when I say that VRECT is at 500mV. What is the usual cause of VRECT being below UVLO?

Thanks,
Crawford

Crawford,

The datasheet recommends setting the maximum current about 20% above your expected maximum current.  For 500mA, you would set the maximum current to 600mA and the total RILIM would be 523 ohms.  RILIM is R11 + R12 from your schematic.

For debug of your system, you might consider starting with a larger coil to isolate the coil from the schematic for debug purposes.

The quality factor will not take the coil size delta into account.  

Regards,

Dick

Dick,

Thanks for clarifying RILIM. Unfortunately I don't have the right resistor values available now in the right packaging. We will be ordering another revision of our board to test a number of other components tomorrow but would like to get the wireless charging in a better state to incorporate some of the changes we have discussed. Would you be able to have a brief call with me tomorrow mid morning (Mountain Time) to finalize some questions I have? I will upload a copy of our most updated schematic tonight.

Thanks,
Crawford

Attached is the updated schematic. Each component has an 0402 package. I was hoping to get some help reviewing this document, and specifically confirm the following parts of the setup:

1. EN1 and EN2 and CHG floating

2. All passives 0402 package

3. R21 (RILIM) = 500 ohms for 0.4 A expected output.

4. Use of 10uF and 0.1uF caps off OUT. Did not seem clear in the datasheet

5. Use of 10uF, 10uF, and 0.1uF caps off RECT. Did not seem clear in datasheet.

Thank you!

Crawford

Crawford,

I recommend that the AC1 capacitors (C55, C63 and C64, be larger than 0402 components.  The series resistance of these capacitors is critical as all the current flows through them. Increased resistance equals heating which will result in capacitance changes.

How did you calculate the AC1 values?  What was the Ls' of the coil?  The values seem high to me based on the 12uH Ls.

FOD tuning may be required for your final solution.  This would include R22 and R19.  If possible, allow for two resistors at each location to get a closer fit for your final tuning.

Regards,

Dick

Dick,

Appreciate the follow up. According to the datasheet, we get 8uH for Ls' (inductance at 1V RMS, 100kHz right?). Here's the datasheet. www.abracon.com/.../AWCCA-12R12H11-C01-B.pdf

Space is our biggest constraint here so it's tough to add extra components for tuning and would like to avoid if not necessary. Would you be able to call today to discuss the tuning process?

Thanks,
Crawford

The datasheet lists the Ls - or "free air" inductance.  The Ls' is the inductance of the coil when placed on a specified ferrite material.  The ferrite emulates placement on a transmitter.  For many solutions, measuring on the TX you intend to use when the RX coil is in its end equipment will give the best reading.

I will contact you off-line.

Regards,

Dick