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

[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 

    

[willzhou]

Hi Mike

As you mentions STWBC86 TX input voltage 5V work fine before?

Do you need to adjust tx input voltage like 12V?

What is the original TX design?   

[MikeP]

Hi, Yes when the STWBC86 is powered from 5V it works, but only charges at about 60mA. But when its powered from 12V the IC gets to 100 degs then the over temperature protection kicks in.

What do you mean adjust the input voltage?

Thanks,

Mike

[willzhou · Accepted solution]

1.For TX/STWBC86 12V input voltage, you must set ping in the half bridge, otherwise the energy will be very high for RX.

2.Also i suggest you modify TX/RX Ctank value. TX use 400nF and RX use about 152nf.