Transform the Way You Charge Your Devices with USB Type-C and PD



Meeting the demands of drones and other applications that use USB PD ports and must move smoothly between operation modes

Nowadays, we see more and more electronics with USB Type-C and USB Power Delivery (PD) ports on the market. They range from cell phones, laptops and power banks to drones, power tools, and smart home and portable applications. The USB PD standard allows the transmission of high power after negotiation and presents new requirements for what’s behind the port: the charger IC.

Figure 1: For compatibility with power sources that have different voltage and power levels, a buck-boost charger is a good choice for a multicell battery system such as drones use. (Credit: ollo)

Figure 1: For compatibility with power sources that have different voltage and power levels, a buck-boost charger is a good choice for a multicell battery system such as drones use. (Credit: ollo)

On one hand, as a device, your equipment should be able to negotiate the highest voltage (5-20V) and current provided by the source to charge the battery and provide power to the system. On the other hand, as a host, your equipment should provide the maximum voltage (5V-20V) and current from the battery in the on-the-go (OTG) direction to peripheral devices.

Gaining Popularity
For devices with single- or multiple-cell lithium-ion (Li-ion) battery systems, a buck-boost battery charger is a good solution for compatibility with the requirements I’ve described. When the device is charging, a buck-boost battery charger can buck (step down) the source voltage to charge the battery if the source voltage is higher than the battery, or can boost (step up) the source voltage otherwise. When providing power to the peripherals, a buck-boost charger can buck the battery voltage if the peripheral device asks for a lower voltage, and boost if the peripheral asks for a higher voltage.

Buck-boost chargers have gained a lot of popularity as more and more applications adopt USB PD and USB Type-C ports. Take drones, for example. Drones are power-hungry devices. Depending on the power level and battery capacity, most drones can fly six to 30 minutes per charge. Due to their short flight times, it’s convenient for users to buy extra batteries and have multiple charging options, from charging from the port on the drone itself to using cradle chargers in the car or at home.

Figure 2: An ability to move seamlessly from one operation mode to the next, along with a full complement of safety features, make the buck-boost battery charger suitable for applications that use USB PD ports. A variety of adapters are also readily accommodated with this solution. (credit: Texas Instruments)

Figure 2: An ability to move seamlessly from one operation mode to the next, along with a full complement of safety features, make the buck-boost battery charger suitable for applications that use USB PD ports. A variety of adapters are also readily accommodated with this solution. (credit: Texas Instruments)

Because the USB Type-C port is universal and has high power delivery capability, it is a good choice here. To be compatible with power sources with different voltage and power levels, a multicell battery system, like a drone, needs to take advantage of a buck-boost charger. It’s also critical for users to be able to charge their batteries quickly and safely during flight intervals. The bq25703A and bq25700A support up to a 6.35A charging current and have extensive protection features, including input current optimization (ICO) that helps get the maximum power out of a wide variety of adapters (Figure 3).

Efficiency is also critical in ensuring a good user experience. Equipment with bad charging efficiency becomes hot, especially when the charging is at high power. In buck-boost mode, charger efficiency can be as high as 98.5%. This is 4% higher than a competing solution operating under the same conditions offers. Thus, heat loss is only 27% of competing solution heat loss, making charging much cooler.

Figure 3: bq25703A charging efficiency vs competition in buck-boost mode (credit: Texas Instruments)

Figure 3: bq25703A charging efficiency vs competition in buck-boost mode (credit: Texas Instruments)

Finally, a drone should operate and charge at different temperature conditions. The bq25703A family provides ±0.6% battery-charging regulation accuracy from -40°C to 85°C. This high level of charging accuracy ensures that the batteries are optimally charged across temperatures.

Figure 4: bq25703A application diagram (credit: Texas Instruments)

Figure 4: bq25703A application diagram (credit: Texas Instruments)

A buck-boost battery charger is a desirable solution for applications that use USB PD ports and require smooth transitions between operation modes, adaptability for different adapters and extensive safety features.

Additional Resources

Check out the bq25700A-EVM and the bq25703A-EVM.


Will-Zhou_TIWill Zhou is a product marketing engineer at Texas Instruments, specializing in battery charger products for applications spanning consumer electronics, industrial, and automotive.

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