STWBC86 Overheating

[MikeP]

 

Hello,

I've designed a PCB with a schematic nearly identical to the STEVAL-WBC86TX. The only modifications are a capacitor and coil size change, which I've also implemented on a development board for direct comparison.

On the development board, my receiver PCB performs almost flawlessly, with the only issue being a charging current of around 60mA (which may be unrelated). However, on my new transmitter board, it almost immediately overheats and shuts down.

I've attached an image from WPSTUDIO showing the temperature reaching 100°C before shutting down and repeating this cycle.

Can anyone suggest potential causes for this issue or point me in the right direction for troubleshooting?

Thank you, Mike

[Andrew Neil]

Show the schematic

[MikeP]

[willzhou]

Hi Mike
Have you test STWBC86 pins, any shortage? From your GUI logs, vin change from 12V to 5V, what is STWBC86 input voltage?

Our reference is 5V input, please limited input voltage and current.

What is your application power, 5W or above?

@Didier HERROUIN please help to add comments, thanks.

[MikeP]

Hello,

Your post was helpful, thank you. I've discovered some interesting results:

1. I was initially powering the development board with a 5V USB supply.
2. My transmitter PCB, however, is designed for 12V operation.
3. When I reduced the voltage to 5V on my transmitter PCB, I observed results similar to those of the development board.

My application has low power requirements (less than 5W). The goal is simply to charge a 950mAh LiPo battery in under 8 hours.

Given these observations, I'm puzzled as to why I'm experiencing overheating issues at 12V, but not at 5V?

Thanks

[Didier HERROUIN]

Hi Mike,

I confirm that if you target 5V output at Rx side, you should supply the STWBC86 with 5V.
What is your targeted current at Rx side ? And please describe your receiver.

What is the inductance value and the size of your Tx coil ? 

Finally, please check your layout to confirm that you follow the layout guidelines provided in the Application Note UM3161, and that you have designed a ground plane below the chipset.

Regards,

Didier

 

[MikeP]

Hello. 
Thanks again for your help. I will send a snippet of my receiver circuit when I am back at my desk (tomorrow) and I’ll also send across the coil information.

My receiver is powered from my lipo battery 3.7v nom. I guess this is an issue?

The layout does have a ground plane underneath the chip. 

[willzhou]

Hi Mike
Our reference design is for 5W application and input is 5V or 5.5V,
also for RX side, power should be RX vout 5V output, then connect to battery charge, then to the battery.

[Uwe Bonnes]

Overvoltage on pins ofter leads to overheating, partial with some MCU functionality still working.

[Didier HERROUIN]

The Rx coil inductance (26µH) seems high.

As the ratio between Rx and Tx coil is high, it generates high voltage on Rx. If it triggers over-voltage protection, the Rx could short Vrect to GND (to confirm as it is not a ST chipset), generating high current on Tx. This high current could be the root cause of the STWBC86 heating (especially if you did not place any ground plane for thermal dissipation).

Please measure AC1/AC2 signals on Tx,  and Vrect/Vout on the receiver.

 

[MikeP]

I have attached some images of my scope. Yellow is AC1 on Tx and Blue is RECT on the Recieve