About Qi standards

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09/29/2018
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In 2014, the WPC wireless charging alliance released the Qi wireless charging standard of 1.2 major version, which will be updated by sub-version iteration in the following years.Recently, WPC released the latest Qi standard on its official website, version v1.2.4. This agreement will be enforced starting from March 8, 2018, which means the certified wireless charging products after March 8, 2018 will no longer apply to Qi v1.2.3, but have been certified according to the standard Qi v1.2.4.

Major changes in the Qi protocol

Regarding apple 7.5w terminal certification, relative to Qi v1.2.3, Qi v1.2.4 has the following updates:

1. This TX type mp-a11 was officially incorporated into Qi standard at Qi v1.2.4.

2. Under Qi v1.2.3, this kind of transmitter is certified by BPP+FOD Extensions, while under newly released Qi v1.2.4, the certification level of the transmitter is simplified, and it will be certified by EPP (mp-a11).

To sum up, after the new protocol is enforced, the type of Qi certification required by apple’s 7.5w transmitter is EPP (mp-a11).

Interpretation of wireless charging transmitter scheme in the market

At present, there are two types of wireless charging transmitters on the market:

The first kind of transmitter is medium and low range, and the scheme is variable frequency and fixed frequency modulation duty ratio.

The working principle of frequency conversion architecture is to adjust the transmitted power by changing the working frequency, which will cause certain interference to mobile phone circuits in some transmission frequency bands.At present, the transmitter of frequency conversion architecture in the market generally adopts A11 or A11a, which can only pass the BPP certification.The power of such transmitter is generally greater than 5W and less than 10W, and there is no Q value detection circuit. The performance of FOD (metal foreign body detection) is obviously inferior to that of the emitter which has passed the BPP+FOD Extensions and EPP certification scheme.

Some launchers support apple’s 7.5w quick charge by adjusting duty cycle duty ratios based on A11/A11a.The transient response of this architecture is poor. Generally, the transmitter of this architecture does not have a Q value detection circuit, which is poor in FOD detection, does not meet the EPP requirements, and cannot pass the EPP certification.As a kind of Chinese innovation, the space-ratio architecture of fixed-frequency modulation wins the high cost performance. To some extent, it also enables users to enjoy the apple quick charging experience at a lower price, but it cannot achieve zero interference on the phone.What’s more, it doesn’t conform to the MFi specification, nor does it belong to the standard architecture of Qi, which may not meet apple’s stricter fast-charge requirements in the future.

The second type is a transmitter that supports apple’s 7.5w, with a fixed-frequency voltage regulator.

Fixed-frequency voltage regulation is the standard scheme officially designated by apple. The 7.5w rapid charge proposed by apple at the MFi conference adopts the framework of fixed-frequency voltage regulation.The mp-a11 topology is adopted, the working frequency is fixed at about 127KHz, the duty ratio is constant at 50%, and the transmitting power is controlled by adjusting the voltage.It can effectively avoid the frequency band of mobile phone, so as to minimize the interference of wireless charging on mobile phone.With Q detection circuit, it will be more sensitive in FOD detection and meet the requirements of EPP.The solution can be certified by BPP+FOD Extensions and EPP.After WPC Qi v1.2.4 is executed, it is uniformly classified as EPP certification.

What performance should customers care about?

The wireless charging power of mobile phones now and soon to be released is greater than 5W, so the selected transmitter scheme should be certified by Qi v1.2.4 EPP.At the same time, the performance of charging stability, charging efficiency, FOD, interference to mobile phones should also be paid attention to.Therefore, it is a good choice to select the architecture emitter scheme of frequency and voltage regulation specified by apple.

Conclusion

According to the current trend, wireless charging will be the standard of consumer electronic products such as mobile phones, while the Qi standard has already occupied a dominant position in this field.The WPC wireless charging alliance released Qi v1.2.4 version update this time, which will further regulate the wireless charging market and promote industrial upgrading, and the competition in the wireless charging market will become more fierce.

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