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Using NXQ1TXH5 in pairs

Question asked by Damien Genouille on Apr 18, 2019
Latest reply on Apr 25, 2019 by Tomas Vaverka

Hello NXP Team,

 

I'm working on a product working as a pair of devices. Each device is charged using one wireless chargind board based on NXQ1TXH5 (aka "charger board"), the design is very close to the reference design (except FOD that is disabled).

Both charger boards are powered with the same USB port (the cable has a Y shape).

 

Each charger works fine individually, however when I use both chargers at the same time (both charger boards LED indicating an on-going power transfer) and then remove one from a receiver device, its LED stays on as if it was still attached to the device. The LED only goes off when I remove the second charger from the second device. 

 

Since there is no other link except power (USB 5V & ground) from one charger board to the other, it looks to me like the charger that is not attached to the receiver interprets the messages sent from the other charger that is still attached to the second device as if it was for him.

 

Looking at the 5V line, I can see around 250mV of noise that I believe matches the communications of the other charger (frequency of the larger pulses is around 2 to 4 kHz):

 

Do you have any idea of what could be done to have two NXQ1TXH5 working together on the same power supply?

Thank you.

Damien

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