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BQ500212A TX design about the operation temperature

Other Parts Discussed in Thread: BQ500212

Hi support,

I design in BQ500212 in my project and my project is a WiFi access point with WPC function. When I do the thermal test with full loading, the temperature in the enclosure is about 70C. The WMP chip is more than 80C. Maybe more than 80C. I use TI RX evb with 950mA loading to be the receiver. I see the output voltage will start to decrease from 5V to 2.xV slowly. When I change the loading to 500mA immediately, the 5V will come back. In 25C room temperature, the output can keep 5V without decreasing.

What is the main root cause for this? I have used 4 C0G 0.1uF caps and removed the NTC to disable the thermal cutoff function. Does test temperature in the chamber is too high (45C, for full loading, the enclosure inside is hot) to let the caps to degrade to less value to shift the resonator frequency? I think the PWM chip and the controller should not be the thermal sensitive components. 

Your comment will be helpful for me.

Thanks.

  • I found if I change current sense resistor to 0 Ohm, the voltage drop issue will be solved. I am not sure the symptom related to FOD since the LED_A is still blinking when voltage is dropping. It means the status is still under normal operation. It's weird! As I know, removing current sense will be a non-Qi device but the current sense for output voltage stability makes me trouble.  What's the suggestion operation temperature for this?

    Any idea for this?

    Thanks.

    Franky