BQ51050B: BQ51050BRHLR connection to transmitter is in short spurts

Hi Steve,

Can you share the Vrect voltage? It sounds like there may be an error in startup. Are you able to look at the EPT packet that is being sent by the RX?

The following is an FAQ for good places to start for debug: https://e2e.ti.com/support/power-management/f/power-management-forum/910420/faq-startup-troubleshooting-for-wireless-power-rx

Best Regards,

Anthony Pham

Anthony,

I've attached the Vrect and TS-CTRL output. 

Also, the Vrect is a 2v/Div.

Thanks

Steve

Hi Steven,

Do you have the L and L' values for the coil? I'd like to verify the series and parallel capacitance that you've chosen. Have you done FOD tuning for the receiver?

Best Regards,

Anthony Pham

Anthony,

L is 27uH.  L' is 36uH.  We have not tuned the FOD.

Thanks,

Steve

Hi Steven,

Would you be able to try the FOD calibration: https://www.ti.com/lit/zip/sluc577 ?

We don't have the equipment for the FOD calibration.  After reviewing FOD calibration comments within the Forum, it seems like the FOD can be improved by increasing the FOD to GND resistance (200 ohms) and decreasing the ILIM to FOD resistance (110 ohms) while maintaining the overall resistance the same.  Unfortunately, I didn't see any guidelines.  Do you have suggestions for this trial and error method? 

Hi Steven,

Looking over the waveform again, this may lead to more of a communication issue between the TX and RX. The issue could possibly be the size of the coil. Do you have information on the coil size? With the design, anything greater than 20mm or greater will work. 

On the TX side, I'm using TDK:WT303012-12F2-ID, which is 30mm (6.8uH).  On the RX side, I'm using TDK:WR151580-48F2-G, which is 15mm (27.1uH)...

We have another design using the bq51050 with a Wurth coil: 760308102207, which is 40mm (8uH), that exhibits the same disconnect/reconnect issue. We are using the TYLT charger in this application. This is why I was thinking this might be a receiver FOD issue.

Hi Steven, 

The RFOD value would be something you can adjust here. Generally, it's recommended to start with 200 Ohm, which you have, and increase if needed. Can you try 225 Ohms if you believe it is FOD issue?

I tried RFOD of 225 and 215.  Not much of a difference.  It stays connected for over an hour, then it goes into the disconnect/reconnect sequence....

Hi Steven,

Interesting, can you share the following:

• BAT voltage if you are charging a battery
• Voltage at the RECT pin
• Voltage at the OUT pin

Best Regards,

Anthony Pham

The chart shows Rect vs Battery voltage.  The battery voltage started at 3.4V.  It charges good until the battery voltage reaches 3.8v.  Then it starts to disconnect.  If I disconnect the battery for a couple hours, then it will charge it fully to 4.15v. But it rarely charges from 3.4v to 4.15v.

In this case, it did charge from 3.4V to 4.15V.  The Rect output looks crazy after an hour of charging, which is completely different than Figure 23 of the datasheet.

Hi Steve,

That's very interesting. Are you able to monitor the EPT packet as it's charging? The device could also be overheating as the RECT voltage looks to be a bit lower than typical. 

Best Regards,

Anthony Pham

I don't have anything to monitor the EPT.  What is your suggestion?  I have a commercial board using the b1500212B.  Is there a way to pull the data from that board?  Or is the only option to get the Qi Sniffer from Avid?

Hi Steven,

It is recommended to use the Qi Sniffer from AVID. Another option is to use the BQ500212A and the TX Tuning tool. 

If this isn't possible, we can try strengthening the communication between the device as this could also be a communication issue. Can we try and increase the COMM capacitors so it is 20% of the series capacitors (double the current value) or 30%?

Best Regards,

Anthony Pham