Cut the charging cable TI wireless charging solution to unlock a variety of applications

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Apple and Samsung are the two major mobile phone manufacturers that brought wireless charging into the public eye: in 2015, Samsung released the Galaxy S6, a mobile phone that supports wireless charging; in 2017, iPhone 8 and iPhone X became Apple's first mobile phones that support wireless charging. Since then, domestic mobile phone manufacturers such as Huawei and Xiaomi have also tried wireless charging, and this technology has once become a new trend in mid-to-high-end mobile phones.

Wireless charging products are increasingly popular among consumers for their convenience, reliability and safety. In addition to mobile phones, more and more wearable devices such as TWS wireless headphones and smart watches that support wireless charging are constantly entering the market. At the same time, different types of wireless charging devices are gradually integrated into our life scenes, such as IKEA's launch of a desk lamp with a wireless charging base and Xiaomi's launch of a 30W super wireless flash charger.

Wireless Charging System

The wireless charging system is mainly composed of three parts: power supply, wireless charging transmitter and wireless charging receiver. The above figure shows the main components of the whole system, and the figure below shows its circuit diagram. How does the wireless charging system work? The following is a brief introduction to its working principle:

Wireless charging system circuit diagram

The wireless charging transmitter (Tx) is usually powered by a 5V to 20V DC input power supply, which comes from an AC/DC power adapter or a USB port. Some special applications (such as reverse wireless charging of mobile phones) may also power the battery.

The wireless power controller can drive a half-bridge or full-bridge converter to transfer energy and regulate the transmission power through communication with the receiver.

The transmitter coil transmits power through electromagnetic induction, and the energy is coupled to the wireless power receiver (Rx). The receiver receives energy through a similar coil and provides energy to the subsequent stage through rectification and power conversion circuits (such as charging circuits).

The receiver can send commands through the communication interface to adjust the charging voltage and can also terminate power transfer completely after receiving an indication that charging is complete.

To improve the working efficiency of the wireless charging system, the bus voltage Vbus required by the coil in the wireless charging transmitter (Tx) can be designed to vary with the transmission power: when fully loaded, the transmission power is the largest and the bus voltage rises to the highest; when in standby mode, the transmission power is the smallest and the bus voltage also drops to the lowest.

As mentioned above, the power Vin of the wireless charging transmitter may come from an AC/DC power adapter or a USB port (5V to 20V), or it may be powered by a battery, with a wide voltage range. In order to match different power supply voltages and the bus voltage required by the transmitter coil, a DC/DC converter can be used to adjust the voltage between Vin and Vbus, and the DC/DC converter topology mainly depends on the potential relationship between the power supply voltage Vin and the bus voltage Vbus required by the coil.

For example, for a 30W wireless charger, the input voltage Vin is provided by a 12V power adapter, and the bus voltage Vbus is designed to be adjusted in the range of 2V to 20V. At this time, a buck-boost converter is needed to meet the voltage matching between Vin and Vbus. Some wireless chargers are designed to save costs and sacrifice standby power consumption. In the standby state, the bus voltage of the transmitting coil is designed as the input voltage, so only a boost chip is needed to meet the Vbus voltage requirement during charging.

Texas Instruments boost and buck-boost solutions for wireless charging devices

Texas Instruments offers a range of boost and buck-boost products to meet the design needs of wireless charging transmitters in various power ranges. The following will briefly introduce the optimal solutions of Texas Instruments products in different application scenarios.

Boost and Buck-Boost Controllers for Wireless Chargers

At present, the power of wireless chargers on the market ranges from 5W to 30W. As consumers' demands for wireless charging are mostly efficient and fast, high-power wireless chargers have become a new trend. In addition, wireless chargers that support charging multiple wireless devices at the same time are also increasingly favored by consumers for their good user experience. The figure below shows an application scenario where a wireless charger can charge a mobile phone, a watch, and a headset at the same time.

Wireless charger

The figure below is a schematic diagram of the wireless charger circuit. To adapt to adapters with different rated voltages, the input voltage range is designed to be 5V to 20V. In standby mode, to reduce standby power consumption, the output voltage can be designed to be as low as 2V; under full load, the output voltage needs to be increased to the maximum design value to obtain optimal transmission efficiency. For example, in a 30W wireless fast charge, the maximum output voltage of the buck-boost circuit is generally set to around 20V.

Application of buck-boost solution in wireless charger

Texas Instruments LM34936 is a four-switch synchronous buck-boost controller with a built-in 2A MOSFET driver. The maximum output voltage can reach 30V. It has a small package and high efficiency, and is suitable for the design needs of high-power wireless chargers.

If you want to reduce costs, you can choose a boost controller solution. Texas Instruments' synchronous boost controller TPS43061 can significantly improve operating efficiency and reduce heat loss compared to ordinary non-synchronous boost solutions, making it an ideal solution for high-power wireless charger designs.

Application of boost converter in reverse wireless charging mobile phone

In recent years, reverse wireless charging has also become one of the trends in mid-to-high-end smartphones. Smartphones are not only a communication tool, but also a multifunctional smart electronic device that can wirelessly charge TWS wireless headphones, smart watches or other mobile phones, as shown in the figure below.

Support reverse wireless charging for mobile phones

The circuit diagram of reverse wireless charging for mobile phones is shown in the figure below, where the boost converter can be TPS61372 or TPS61089 from Texas Instruments.

Application of boost solution in mobile phones supporting reverse wireless charging

TPS61372 has the following significant advantages in mobile phone reverse wireless charging applications:

Wide range voltage output up to 16V, reducing coil current and coil loss;

The overall solution is small in size, simple in design, and low in BOM cost

The chip adopts a small WCSP package, which is only 1.57mm×1.52mm×0.5mm, which is particularly suitable for mobile phone applications;

Supports 1.5MHz high switching frequency, which can effectively reduce the size of external inductors and capacitors and reduce costs;

Few external components and simple design;

PFM mode or PWM mode can be selected under light load to flexibly meet customers' requirements for light load efficiency or EMI design .

With true shutdown function, when the chip is not working, the input and output terminals are truly shut down to reduce standby power consumption.

Application of boost converter in wireless charging mobile power supply

More and more mobile power banks that support wireless charging are emerging, and their wireless charging circuit structure is similar to that in mobile phones. Currently, the wireless charging power of mobile power banks ranges from 5W to 20W, and Texas Instruments' boost converters TPS61089, TPS61088, and TPS61178 can be used for this application.

Wireless charging power bank

The maximum output voltage of TPS61089 and TPS61088 is 12.6V, and they support the maximum switch current of 7A and 10A respectively; the maximum output voltage of TPS61178 is 20V, and it can provide the maximum switch current of 10A. These three chips of Texas Instruments are synchronous boost converters with integrated upper and lower tubes, which can meet the design requirements of 5W~20W wireless charging mobile power supplies.

Texas Instruments will continue to launch boost and buck-boost solutions for wireless charging applications. Click here to follow the TI Application Center to get the latest information on boost products, buck-boost products and related reference designs.

(Author: Eileen Zhang, TI E2E Chinese Community)