I am Finding wireless charging guru ▶ Heat comes out while Wireless charging.

[JAKE2]

Hello everyone !

I am using STWBC86 and STWLC38 MCUs, using our own custom board.

The wireless charging was going well, but the problem is this.

[ When charging → put away the RX → put back the RX ] ...▶ the heat comes out from the RX MCU.

Any ideas to solve this issue ? Thank you.

[JAKE2]

While catching up the Qi. V.1.3 contents, the Tx will not transfer power untill the "Ping ▶ Configuration ▶ Negotiation" protocol cycle, then where would the Tx's transmit power go during these process?

I am assuming that these power (during protocol phases right before Power Transfer) are going to dissipate into heat, from the internal part of RX IC. 

[JAKE2]

To reduce heat, I changed two parameters on the TX's side, using GUI.

① I changed the TX frequency from around 146kHz to 160kHz (the heat reduced, much better. But it needs additional modification to handle the heat issue, because the heat still comes out)

Using frequency above around 170kHz, cannot charge to my custom board.

I think the frequency and  power efficiency are trade-off-relationship.

② I changed the re-ping delay parameter from 1,000ms to 300ms

The register is located at Tx Registers ▶ Tx Configuration ▶ "TX PING INTERVAL" register.

The interval of heating issue has reduced, but there is still heat, at times. And I do not know what side effect will happen. 

[JAKE2]

When using STWBC86 and STWLC combination, the charging is excellent.

No heat comes out from TX's side, neither as well from the RX's side, when charging as usual.

The heat problem occurs when I intentionally repeat attaching and dettaching so many times

(to be precise, I am making problem intentionally , to secure the safety of heat comes out for some reason) 

And while I'm reading Qi. V.1.3 document, I got insights, those are..

To maximize TX PING DURATION, and to minimize TX PING INTERVAL.

It worked pretty well, but still heat comes out from RX. 

I am not sure my experiment is going well, are there somebody in similar case ?

[JAKE2]

While I am looking around RX Configuration Qi, what is RP24 ?

I had been heard about RP or RP8, but never heard of RP24. Could you tell me what is it ?

+) It seems like my wireless charging set is not ready for EPP, because it can not reach to negotiation phase

(TX PTC UPDATE LTCH is always "Did not occur" - status)

I wonder the Qi 1.2.4 Tx and Qi 1.3 Rx is compatible to coply EPP ▶Negotiation and Renegotiation

Sincerely Yours,

Jake Kang

[JAKE2]

I just happend to found out the reason for Rx heating, it was because I set too high voltage for ARC threshold.

I changed the setting from 6V(original value) to 4V(new value), and the problem was wiped out, it works well.

[JAKE2]

Now I am facing the problem regards to using power Multiplexer, get input two inputs separately( Wireless charging voltage , USB-C Type 5VDC) and outputs the single supply among the two inputs.
The problem is, as far as I understand, the wireless charging's output voltage does fluctuates so hard while Mux's safety input voltage range is narrower than the former, so the Multiplexer seems constantly continues resetting on and on.

I will attatch very simple diagram of the Multiplexer IC ( It's made from another company, but I guess you well aware)

 I've tried connecting directly the wireless charging's output node into the Load, removing the power mux IC, and it worked.
Does anyone developed wireless charging with the option of using USB type wired charging as well?

Or could you recommend the power Mux that can possibly use with wireless charging IC ?

Sincerely Yours, Jake Kang.

[JAKE2]

I have tested three different case, could anyone recommend a power mux IC instead of TPS2116 ?

[Didier HERROUIN · Accepted solution]

Hello,

The output voltage from STWLC38 is not supposed to oscillate, it should be stable as it is a LDO output.
Could you attach a zoom of the period of time where VIN2=5V and then it falls ? It is difficult to see on the plot the behavior of VIN2 and if it exceeds 5.5V.
If you suspect a overvoltage protection by TPS2116, you could try (for testing purpose) to set Vout=4.5V using STWLC38 GUI.

Then, which configuration do you use inside STWLC38 ? I understood that you have modified several parameters, it may be a reason of instability. For instance, if you have increased the minimum operating frequency, you will get less power available at Vout. In your 3rd case, have you tested that Vout is still stable when you draw some current ? 
What is the maximum of power that you need at Vout ?

Regards,

Didier

[JAKE2]

Case #1, USB OFF

↑ Here's the zoomed Waveform.

Then, which configuration do you use inside STWLC38 ?

■ RX ARC THRES = 6.0V → 4.0V

■ RX BPP VOUT SET = 5.0V → 4.5V

when adopted  the voltage that you metioned, the it works well to do so.

In your 3rd case, have you tested that Vout is still stable when you draw some current ? 

→ I haven't tested yet, it just starts working fine from today. 

Thank You