Leading the Charge Seminar – Getting into the Details

Chris Stephens
General Manager – IDT Mobile Power and Sensing Divisions

Greetings again from Shenzhen! This is the second post covering highlights from our Leading the Charge Seminar in Shenzhen. You can read about the opening sessions in Setting the Stage in Shenzhen.

As we continued the morning, Rui Liu head of Product Definition and Applications took the assembled attendees through all of the intricacies of Wireless Power standards. He described BPP (basic power protocol for up to 5W) and EPP (extended power protocol for up to 15W). Rui also addressed the all-important in-band communications protocols whereby the Tx and Rx communicate with each other via FSK and ASK modulation.

These standards are administered by the Wireless Power Consortium which was founded in 2008 to propagate an industry standard for wireless charging. The standards, collectively known as “Qi” are in great hands and have dominated wireless power deployment because the top mobility companies in the world sit on the board of WPC including:  IDT, TI, Samsung, LG, Apple, Qualcomm, NXP, Verizon, Panasonic, and Toshiba. Click here to see the entire board membership.


Next Zhitong Guo (one of IDT’s star applications engineers) talked about resonant tank design. For magnetic induction (the principle on which the Qi universal standard is based), designing the Tx and Rx resonant tanks are a critical element of the integration process. The key concept here is that the “gain” of the resonant tank network varies with the operating frequency. By accurately modeling this gain, one can develop a robust wireless power system with very high dynamic range by adjusting the operating frequency.

Next up were Rui Lui and Nicholaus Smith who took the crowd through IDT’s Qi transmitter design guide. In an extended two-part session they covered everything from how to implement the ASK demodulator filtering and how to do Foreign Object Detection (FOD) to how to implement the Tx for lowest EMI (electromagnetic interference) which is critical for using wireless power in smartphones. IDT has shipped more transmitters than any other supplier and we have perfected the transmitter design and applications techniques to ensure best user experience. Nicholaus took us on a brief tour of implementing transmitters in an automotive cabin environment, as well.


Next, one of our Seminar sponsors, Sunway, took the assembly through the details of Wireless Power coils. Wireless Power systems are very efficient (up to 88%) and getting more efficient, but it is important to note that ~50% of the loss in wireless power systems is due to the coils. Companies like Sunway are working to advance the coil design to reduce this loss and allow for higher and higher charging power.

Finally, Zhitong retook the stage and took us through all the intricacies of Receiver design. The audience was rapt as Zhitong held forth on bridge rectifier modes of operation:  Diode Mode and Synchronous Mode. IDT has perfected existing techniques such as Zero Current Sensing and Dead-Time adjustment to ensure minimum switching losses and highest efficiency for our customers. I guess that is why we have sold over 200 Million wireless power receivers in the last four years. Zhitong further went on to describe the all-important Control Error Packet and how it governs wireless power operation. Finally, as you might imagine, the transient response of the Rx IC to changes in load is critical, so Zhitong explained in detail how IDT manages the transient response for maximum robustness.

That wraps it for the middle of the day. Next up is coverage of session 4 and our Panel discussion.

Check out idt.com/wirelesspower for more technical information and design resources.