BQ51013B: BQ51013B doesn't work with small diameter chargers

Hello

First thing to check would be the voltage at RECT pin during start up it should be greater than UVLO, 2.7V. 

If voltage is less than this check the coil tuning, instruction are in data sheet section 8.2.1.2.2. (update)

Bill, RECT rise up to ~10V every 200ms. Is it right behavior? Need i tune coil? If NO why my device did not charge from little chargers?

The voltage looks high enough to start and voltage is below OVP (15V).

RX should try to communicate with the TX, should see modulation on the RECT about 40mS after the voltage goes above UVLO. See attached.

Tuning could still be an issue, L of the 760308101214 is double the typical coil and Cs caps would need to drop by 50%.  Once this is doe the comm1 / comm2 value may be too high.

0447.bqTESLA FAQ--Start up.pdf

Hello

Any update on this problem?

Hello, Bill!

Not really. I found a coil that start works with Galaxy Watch charger (but only 0.5s)

But this coil don't work with Apple Watch charger.

I continue to select the coils ...

Sorry for the delay getting back to you on this.

Are  you still seeing the 0.5 s operation with the Galaxy Watch charger?

Hello, Bill!

Now I see the next waveform on VRECT. Why does VRECT drop down after 3 seconds?

When I wrote about 0.5s, I looked at a regular multimeter and therefore could be wrong.

What could be happening.

After the RX sends SS/ID/Config the RX will start tuning TX operating point to 7V at RECT.  That is what we seen in the first 3 divisions (1.5 sec).  During this time the output is OFF, no load.

At 7V the output turns ON and load is applied.  We see the voltage drop.  That is the next 1.5 sec and then TX turns off.

What is causing the TX to turn OFF -- one clue is 1.5 sec, if the TX does not receive a Control Error Packet (CEP) is 1.5 sec it will restart.  The other thing we see is the operating point is not changing, RECT voltage not changing for last 1.5 sec.  This points to a communication problem, the TX is not decoding the CEP.

What are you using for Comm 1 and Comm 2 capacitors?

Do you have a schematic you can send?

Bill, COMM1 = COMM2 = 44nF . Is it right values?

//Do you have a schematic you can send?

Yes but there are no nominals. ok I'll make schematic with nominals.

This looks a little high.

Try sizing the Comm caps to 10% of the Cs caps. This would be the caps in series with the RX coil and tuned to 100kHz.

Hello, Bill! Oh, i.e. shuld I remove C28, C31 and change C22, C25 to ~7.1u ?

Are other components compatible with 760308101214 (L = 26 μH, DCR = 520 mOhm, L '~ = 35.6 μH)?

I calculated for this coil Q = 314, and capacitors 71n and 975p. Are these the correct values?

You also wrote earlier:  //L of the 760308101214 is double the typical coil and Cs caps would need to drop by 50%.

So are 760308101220 with L=12.6uH and R=340mOhm is better than 760308101214 choice?

Also i have WR202010-18M8-ID with 11uH and 350mOhm and AWCCA-30R30H05-C01-B with 29.5uH and 1.8mOhm DCR (Q > 100k)!!!

Which of these coils is better?

Is the last one (with Q>100k) suitable for Qi receivers?

 
I also attach part of the circuit with BQ51013B:

Hello

Should I remove C28, C31 and change C22, C25 to ~7.1u ? Bill J -- First try removing C28 and C31, if that does not work try 7uF.

Are other components compatible with 760308101214 (L = 26 μH, DCR = 520 mOhm, L '~ = 35.6 μH)? --- Bill J -- Looks good

I calculated for this coil Q = 314, and capacitors 71n and 975p. Are these the correct values? --- Bill J -- Looks good

You also wrote earlier:  //L of the 760308101214 is double the typical coil and Cs caps would need to drop by 50%.

So are 760308101220 with L=12.6uH and R=340mOhm is better than 760308101214 choice? -- Bill J -- 214 with higher L should be better.  As coil size goes down then coupling factor goes down.  To off-set this increase coil L.

Also i have WR202010-18M8-ID with 11uH and 350mOhm and AWCCA-30R30H05-C01-B with 29.5uH and 1.8mOhm DCR (Q > 100k)!!!

Which of these coils is better? --Bill J-- I am going to say the higher L at this point.

Is the last one (with Q>100k) suitable for Qi receivers?---Bill J -- Yes

Also

Double check the coil connection --- COIL 1 is in the right spot

But did not see COIL 2 connection.

Hello, Bill! Sorry: Coil 2 connected to AC2 (according to Simplified Schematic of datasheet).

Hello, Bill!

//Bill J -- First try removing C28 and C31, if that does not work try 7uF.

Without C28 and C31 VRECT drop after ~3s. Even with C22 and C25 equal to ~7nF VRECT drop after the same time.

This is occur with and without load (0mA, 10mA, 80mA).

May be problem in Ros, Rfod or R1 resistors?

Hello, Bill!

Even decreasing ROS to 20k does not help...

Oh! I see the difference betveen my VRECT signal and signals from other developers: https://e2e.ti.com/support/power-management/f/196/t/721489?BQ51013B-BQ51013B-Problems-with-initialising

At digital transmittions my VRECT level decrease. 
For others, it is increasing. Is it problem?

The change during communication, Buck (decrease) or Boost (increase) will vary with load and tuning.  It is common to see a boost at light loads then at higher loads it changes to buck.

Are all you test with the Google Watch TX and Apple Watch TX?

Hello Bill!

//The change during communication, Buck (decrease) or Boost (increase) will vary with load and tuning.  It is common to see a boost at light loads then at higher loads it changes to buck.

That is, the oscillograms that I see are quite correct?

//Are all you test with the Google Watch TX and Apple Watch TX?

Unfortunetly i have not Google Watch TX and Apple Watch TX...

One option to consider for a small coil transmitter.  Many of the 5V transmitter will operate with a 30mm or 20mm coil.

The FOD tuning will not be accurate but power section and demodulation should work.

Some options below:

1.) TDK WT303012-12F2, 30mm round 6.3uH

2.) Wurth 760308101103, 30mm round 6.5uH