Smartphone microUSB port data line protection scheme

1. Problems with smartphone micro USB port

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At present, smart mobile phones on the market, most devices combine large screens and multiple functions, and also require devices to work for a long time, which is bound to require a larger capacity battery to support this feature. The increase in battery capacity, if it is still charged according to the previous small current, will inevitably increase the charging time, which will greatly reduce the user experience of the smartphone. If you need to charge the same time, or can complete 90% battery charging in a short time, you must use a mobile phone charger with a larger charging current.

Therefore, in order to comply with this change of smart phones, the mainstream mobile phone chargers on the market have changed from the previous 500mA~700mA charging current to the charging current of 1A~2A. The increase of the charging current also puts forward higher requirements for the charging data line, not only the thickening of the power line and the grounding line in the data line, but also the reliability of the contact of the small microUSB port. high. If the microUSB port has poor contact during use, or if something falls into the body (like sweat or the like), then there will be a lot of power consumption at the microUSB port during 2A current charging (I2R). The relationship), if this power consumption greatly exceeds the range that the mobile microUSB port can withstand, the port will heat up, and then burn black, in severe cases, the phone will be burned and a fire will occur. In the actual use of smart phones, cases of mobile phone burning or even explosion have also been heard, which poses a major danger to the personal safety of consumers. The security protection of smart phone microUSB ports has become an urgent need for many manufacturers. Question.

For the above risks of the microUSB port of the smartphone data line, TE Connectivity (hereinafter referred to as TE) Circuit Protection Division has proposed a solution to use the polymer positive temperature coefficient recoverable resistor (PolySwitch product) installed on the microUSB data line. Internal effective temperature protection. Let's first introduce the PolySwitch product.

2.PolySwitch product features

TE's circuit protection division PolySwitch device is a composite of semi-crystalline polymer and conductive particles. At normal temperatures, the conductive particles form a low-resistance grid in the polymer (as shown in Figure 1). However, whether the current through the device rises or because the ambient temperature rises, the lens within the polymer will melt and become amorphous when the temperature is high to the switching temperature (TSw) of the device. During the melting of the lens, its volume will increase and the conductive particles will be separated, resulting in an increase in the nonlinearity of the device resistance.

Figure 1 PolySwitch works

As long as the externally applied supply voltage remains at this level, the device will remain locked in the active state (ie, the device will remain latched in the protected state). Once the voltage drops or the power is turned off and restarted, the PolySwitch device will return to normal operation.

3. TE's micro USB port protection scheme introduction

From the above, TE's Recoverable Resistor PolySwitch product is a device that can achieve over-temperature and over-current protection. In the smart phone microUSB port data line protection scheme, simply connect the PolySwitch device to the microUSB interface Vbus power supply. As long as the PolySwitch product detects that the temperature of the microUSB port exceeds a certain value, the safety resistor can be restored and the resistance is increased. Thus, the charging current of up to 2A is cut off, and the temperature of the microUSB port is cooled down without damaging the port.

In use, it should be noted that the PolySwitch product should be placed on the side of the microUSB data line to effectively protect the port from failure. If the PolySwitch is placed inside the smartphone, that is, the power input of the mobile phone, although this method can effectively protect the internal short circuit and overcurrent of the mobile phone, it cannot effectively protect the fault occurring on the microUSB port because Due to the presence of foreign objects at the port, a low-resistance loop is formed on the microUSB port, and the current of the mobile phone charger can be returned to the charger circuit via the low-resistance loop of the microUSB port, that is, the current does not flow to the inside of the mobile phone. Figure 2 is a simplified diagram of the smart phone microUSB port protection. One principle of circuit protection is that the protection component must be placed upstream of the protected circuit in order to effectively protect downstream electronics. For this type of failure, PolySwitch must be placed at the point of failure before the port to effectively protect, so PolySwitch products are a practical solution inside the microUSB data line.

Figure 2 Smart phone microUSB port protection diagram

For smartphone microUSB port protection, TE's PolySwitch solution has the characteristics of high reliability, low cost and simple use compared with integrated circuit solutions. The integrated circuit solution uses a temperature sensor to detect the temperature of the port, and requires a temperature detecting chip, an NTC temperature sensor, and a control loop. The components are numerous, the design is complicated, and the cost is high. TE's PolySwitch is UL-certified and is a highly reliable component that requires only one component for effective overall protection. At the same time, TE's Circuit Protection Division has decades of experience in recoverable fuse resistors, and the impact of the product and microUSB port installation design is minimized, and the microUSB data line is basically unchanged. Original shape.

4 Conclusion

The microUSB data cable is not only widely used on smartphones, but also has very popular applications on other mobile smart devices such as tablets. TE Circuit Protection has always been committed to improving the security of user use. Many specific implementations have been proposed for the protection of smart device microUSB ports, providing customers with a complete set of protection solutions.

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