The use of integrated step-down chargers for faster USB charging.

In nearly all applications, designers are under constant pressure to reduce load times and reduce chassis size, increase power density, and lower costs.

The use of universal chargers for lithium-ion (Li-ion) and lithium-polymer (Li-poly) batteries with USB 3.0 (PD) power supply for mobile charging (OTG) is growing in a wide range of applications, including drones, smartphones, tablets , cordless vacuum cleaners, portable medical devices, wireless speakers and electronic devices at the point of sale. In all of these applications, designers are constantly pushing to reduce load times and chassis sizes, increase power density, and lower costs.

Booster-step-down chargers in conjunction with USB power supply can enable the development of fast, efficient charging solutions via the universal input. However, these are not simple devices and it can take a long time to design them to support the USB OTG specification. This increases costs and can affect design schedules. The design process can be further complicated by the need to adhere to the USB Fast Role Swap (FRS) timing and control criteria to ensure that the device that supplies power can quickly become an energy receiver to guarantee an uninterrupted data connection.

For universal USB PD charging applications, designers can solve many of these problems by turning to integrated chargers that streamline the design process and support the implementation of fully functional and compact step-down charging solutions that provide high power and fast charging with a small number of parts. and high power density.

This article briefly discusses the need for universal charging based on the USB 3.0 standard and USB Type-C® connector and the complexity of implementing step-down charging solutions using USB connectors, as well as OTG and FRS functions. Next, the benefits of using an integrated device will be discussed, followed by a Texas Instruments integrated step-down charging solution with dual input selector and USB 3.0 power support as well as OTG and FRS functions. An auxiliary evaluation module will also be described, which will help designers start work on the next universal USB PD charger with OTG and FRS functions.

Figure 1: The internal design of a USB PD charging solution can be complex as it has to accommodate very different configurations of battery cells and power supply voltages. (Image credit: Texas Instruments)

First, the USB PD controller (U4) needs to identify the power supply, including: USB battery charging specification version 1.2 (USB BC1.2), standard next port (SDP), charging next port (CDP), dedicated charging port (DCP) , high voltage dedicated charging port (HVDCP), and even custom power supplies. After establishing communication between the USB PD controller and the power supply, the input power supply path management and current measurement (U1) circuit turns on symmetrically connected power MOSFET transistors to connect the input voltage from VBUS to the step-down charger input (U2). The input power path management unit also measures the input voltage and current with a measuring resistor to support over voltage and overcurrent protection.

The additional four MOSFETs in the step-down charger module (U2) allow the input voltage to be increased or decreased depending on the battery voltage. Another power MOSFET and a current measuring resistor at the output of the step-down charger is needed to support the USB PD charger narrow DC voltage (NVDC) power path management and charge current measurement.

NVDC power path management is a specific control protocol that sets the system to a voltage slightly higher than the battery voltage and does not allow the voltage to drop below the minimum system voltage. The minimum system voltage is a voltage level that allows the system to operate even when the battery is removed or completely discharged. In addition, if the system power requirement exceeds the power supply rating, the battery top-up mode handles the system's additional power demand and prevents the power supply from being overloaded.

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