[FAQ] Startup Troubleshooting for Wireless Power RX

Charging begins but stops suddenly

• Check the voltage at RECT to see if the TX is trying to power the RX on, need a pulse of at least 80mS. If the RECT does not reach target voltage of 7V at startup, output will not turn on. Need 2.7V for UVLO then it starts adjusting TX operating point to 7V.
• Check what transmitter is doing, the receiver will tell transmitter to turn off using EPT packet. Thing to look for to ID an EPT packet is drop in RECT at end of a Packet. Check EN1/2 and TS/CTRL setting.
• Device could be overheating and sending internal fault message to TX. When device internal junction temp reaches 150C it will send End Power Transfer 02 (EPT02) to the TX to stop power transfer. TX will turn off but for how long will vary between manufactures. ILIM sets output current for the LDO. When the unit enters current limit power dissipation on the LDO will increase sharply. Check the Voltage drop between RECT pin and OUT pin, this will give some idea the power dissipation on the internal 5V LDO. link to overheating FAQ

Device not responding / never charging

• If the RECT does not reach target voltage output will not turn on. When OUT is on you should see a drop in the RECT voltage and the COMM Packets (CEP) will be at a 250mS rate. If system is having trouble tuning to target they will be at 30mS rate.
• RECT must be greater than 2.7V to start. But it also cannot be higher than max 15V, OVP point.
• If RECT not reaching 7V target, could be due to communications error or system is running out of gain, coil tuning could be off. See C1/C2 tuning FAQ.
• In general, TI recommends a 22-nF capacitor for COMM1 & COMM2 pins. Based on the results of testing of the communication robustness in the final solution, increasing to a 47-nF capacitor may be in order. A clue that communications is a problem is the timing of TX shutdown, first three packets SS/ID/Config will drop immediately. During power transfer must receive one good packet every 1.5sec or TX will shutdown.
• For high L value coils, try reducing the COMM1 and COMM2 capacitor. The COMM caps should be about 10% of Cs (C1) value, if you are using a high L coil that will reduce Cs. The Cs value is determined by the Ls' of the RX coil. Ls' is the measured value of the coil when installed in device case and on the TX. Coil L value in data sheet is free air with no influence from surrounding metal. Ls' and Cs are tuned to 100kHz. As the Ls' value goes up the Cs value will go down to keep tuning at 100kHz.

If RECT appears too low

• Test with evm coil
• Larger coils 20mm+ work better
• With smaller coil, higher L value helps
• Tuning the series resonate caps View C1/C2 tuning Faq here
• Reduce coil to coil distance