What kind of "protection umbrella" does the USB interface need? Wei'an load switch gives you the answer

      In recent years, the Internet industry has been developing in full swing, and the development of e-commerce and hardware manufacturing industries is also booming. An endless stream of electronic devices are becoming increasingly popular in life. As one of the most universal interfaces in the world, the USB interface has been widely used. We have witnessed the transformation from USB 2.0 to USB 3.2, and also witnessed the elimination of non-universal interfaces one by one.

      At the same time, the requirements of major electronic equipment manufacturers for output current have gradually increased, from the previous 5V/500mA to the current 20V/5A. In the application of such high current, if there are no corresponding protection measures, the internal circuit will inevitably be damaged. Statistics show that more than 40% of electronic product failures are directly or indirectly related to the USB interface, and the resulting adverse phenomena usually include system freezes, USB port burnouts, etc. The main reason is that due to the plug-and-play feature of USB, at the moment when the load is abnormal, the power switch will flow a current of several amperes, that is, it is in a long-term overcurrent state, thus causing damage to the circuit and system.

      In this context, USB interface protection solutions have also received attention from major manufacturers, among which current limiting protection solutions have become an indispensable part of the design process. Due to performance limitations, the original discrete solutions have gradually been replaced by integrated solutions.

      Therefore, WAYON, the "Hermes" in the protection industry, launched a dedicated current limiting protection product for USB interfaces - the WP25P21XX series chips, which can meet the needs of miniaturization, intelligence and integration. It has been widely used in TV panels, TWS headset charging cases, mechanical hard disk interfaces and other fields.

USB interface protection umbrella

      The input voltage of WAYON WP25P21XX series products is 2.5V~5.5V, the adjustable current limit range is between 0.4A~2A, the on-resistance is 70mΩ, the static power consumption is 28μA, and the main packaging forms are SOT23-5/6 and DFN-6 packaging, which can meet the application scenarios of small space and low power consumption products.

WP25P21XX series main parameters

Package physical picture

      When in use, the WP25P21XX series products are usually used between the USB interface and the internal power supply. The input and output pins are connected to a 1µF ceramic capacitor to provide working current to the device connected to the USB interface and provide overcurrent protection when the connected load has an overcurrent phenomenon, so that the USB interface can work safely and reliably. It can protect and prevent the power devices inside the chip from being impacted by large currents and enhance the circuit's ability to carry loads.

Application Block Diagram

      The WP25P21XX product improves the system's operating efficiency by using a current detection circuit with a SENSEFET structure, and uses the current detection circuit to monitor the output current in real time. When the load is overloaded or short-circuited, the internal current sampling tube can detect the load current change in time, and by comparing it with the reference current, a negative feedback loop is used to limit the output current to a safe constant current state to prevent the power supply system from crashing due to overload or short circuit. By using precise adjustment technology, two high-precision requirements of 10% and 20% can be achieved.

      The normal operating temperature of WP25P21XX is -40℃~+85℃, which meets the temperature requirements of outdoor applications. It also has built-in multiple protection mechanisms such as undervoltage lockout, thermal shutdown, and reverse current blocking, which can fully guarantee the electrical safety of the product.

WP25P21XX internal structure diagram

      As shown in the figure above, the FLT pin is an open-drain output and requires an external pull-up resistor. If the chip current limiting protection state is activated, FLT is LOW, indicating that a fault has occurred. The microprocessor can detect the fault flag bit and take measures such as fault alarm, which is conducive to fault location, system status display and other operations. Once the fault disappears, it will automatically return to a high level state. At the same time, the fast output discharge function of the WP25P21XX ensures that the disconnected or disabled load will not float. When EN is low, the discharge field effect transistor (FET) is turned on to create a path from VOUT to GND, ensuring that the load can quickly return to a known 0V "off" state.

Better reverse current protection and anti-static ability

      When the USB interface is in use, it acts as a power source for both external and internal device components, which can easily cause reverse current. As shown in the figure below, reverse current means that the voltage at the output of the system is higher than the voltage at the input, causing the current to flow backward through the system. Reverse current can cause damage to the internal circuit and power supply. Depending on the path from output to input, the cable may also be damaged, and the performance of the connector may be reduced. According to PD = IREV*VDROP, when the power reaches a certain level, it may even cause burning.

Reverse current

      The reverse current protection function integrated in WP25P21XX can well protect the USB interface from the harm of reverse current. The internal substrate potential selection circuit is used to monitor the voltage signals of VIN and VOUT ports in real time to always ensure that the power PMOS tube body potential is at the highest potential, prevent the body diode from being forward biased, and thus block the reverse current. In the figure below, WP25P21XX has 5 V applied to the output end and 0 V applied to the input end to demonstrate reverse current protection.

Reverse current protection function test circuit

Peak reverse current

      As can be seen from the figure above, the peak reverse current monitored by the oscilloscope is 12.8 mA.

      In addition to the super strong reverse current protection function, the WP25P21XX series products also have better anti-static ability than similar devices. By improving the uniformity of the trigger voltage of the parasitic BJT between different fingers of the GGNMOS multi-finger structure, it is ensured that all devices are turned on before the final breakdown of the first device, so that all the corresponding BJTs designed are turned on and the current discharge purpose is achieved. The measured ESD (HBM) can reach 8KV, which fully meets the more demanding use environment of users in actual use.

Human body simulation static electricity test diagram

Already supplied in batches to major mainstream customers in the market

      At present, the WP25P21XX series products have been supplied in batches to major mainstream customers in the market, and the products are widely used in TV panels, TWS headset charging cases, and mechanical hard drive interfaces.

Application pictures

Application Schematic

      The above figure is a typical application solution of the WP25P21XX series products in the market. The current limiting switch is placed between the DC-DC chip and the subsequent circuit. When a fault occurs inside the circuit, the current limiting switch limits the current to the set current limiting value to provide protection for the subsequent circuit.

Charging compartment protection circuit

      In the application of TWS headset charging case, it is usually used in conjunction with TVS, which can effectively protect the main chip from ESD and overcurrent.

      The maximum current limit of the WP25P21XX series is 2A. To meet market demand, Wei'an will continue to launch products with a wider output range and a larger current limit.

      WAYON was founded in 1996 and focuses on the field of circuit protection components and power semiconductors. WAYON always adheres to the core values ​​of "customer-oriented, technology-based, and hard work", is committed to leading the market through technological innovation, and strives to become a leading brand of circuit protection components and power semiconductors in the world.