Hello,
I recently created a PCB to use the BQ51221 while using the TIDA-00234 as a reference design. I am able to get a 5V out on both a Qi BQ500212 EVM and a PMA transmitter, however, the system is horribly inefficient. If I increase the output current on my eload past 300mA, the IC enters thermal shutdown. I am trying to troubleshoot why this is happening. Here is the data I have gathered so far.
Efficiency:
TI BQ500212EVM-550
| Rx Circuit | Power In (W) | Power Out (W) | Eff |
| BQ51221EVM-520 | 2.05 | 0.99 | 48% |
| Custom PCB (TIDA-00234) | 356 | 0.99 | 28% |
There is a very audible chirp coming from the custom PCB.
PMA Transmitter
| Rx Circuit | Power In (W) | Power Out (W) | Eff |
| BQ51221EVM-520 | 1.8 | 0.99 | 55% |
| Custom PCB (TIDA-00234) | 3.06 | 0.99 | 32% |
There is a very audible buzzing sound coming from the custom PCB.
As you can see, the custom PCB is being extremely inefficient.
Vrect Discrepancy:
Usually the first thing I measure while troubleshooting is Vrect on the Rx.
The first two oscilloscope captures are of the BQ51221EVM on both BQ500212EVM and PMA transmitter.
BQ500212EVM PMA Transmitter
Here is the Vrect from the PCB.
BQ51221EVM PMA Transmitter
The Vrect on the custom PCB is much higher in both cases which is what I think it leading the inefficiency. If I did I manage to increase the Pout of the chip before thermal shutdown occurred, I noticed that Vrect while the Rx was placed on the BQ500212 did not change like the EVM (Dynamic Efficiency Scaling), it was constant around 9-10V.
Any ideas on why this might be happening to the system would be greatly appreciated, whether that the IC might not be soldered correctly, or if it is a problem with the passives. I have a schematic and layout if needed.
Thanks,
Jason
