In debugging Smart key continuous unlocking trouble troubleshooting process, in order to compare the impact of analog switch ts5a3166 for unlocking data communication, try to short-circuit analog switch input and output foot, never wanted to a black dragon, The input and output of the DC-link chip is shortened (both are sot23-5 packages). The next one on the power to find the DC power supply short-circuit prompt, aware of the supply system short. DC part of the circuit such as. So the problem is, the DC-to input and output are connected together, in other words, the DC-to output voltage, why can cause the power chip burned it? If the problem is to start with the internal structure of the DC-to chip, as shown in the TI company-DC converter TPS562201 (http://www.ti.com.cn/cn/lit/ds/symlink/tps562201.pdf) internal structural block diagram. It can be seen that the power chip output SW is two power tube, when the output SW pin plus voltage (input vin floating in the case), the following circled power MoS tube will be subjected to reverse voltage. While the positive voltage of the power tube is at least dozens of volts, the reverse pressure is only 5 V, so the output pin can be increased to cause the output port power tube burned, causing the power system short circuit. This list of commonly used NPN transistor 9013 illustrates the problem, from the following table can be seen from the emitter to the base of the breakdown voltage of only 5 V, the other transistors and MOS tubes are similar, the reverse voltage is very small. The same is true of other manufacturers ' DC-to converters, with XL1509 (http://www.docin.com/p-773783557.html) as a simple example. The internal structure of the Block diagram is as follows, the same can be seen at the output of a power tube, it is obvious that the increase in its output voltage will cause internal power pipe burned. In fact, it is not just the DC chip output voltage will burn the chip, other power converters will have similar problems. For example, a three-terminal regulator such as LM7812, which adds voltage at the output, can also cause the chip to burn. As the internal structure of the LM7812 block diagram, the same can be seen in the output is a transistor, if the output to increase the voltage, resulting in the transistor to withstand the reverse voltage and burned, resulting in the chip function is not normal. Finally, it is suggested that the protection of the output terminal should be increased when designing DC power conversion circuit. If the pressure drop requirements are not very stringent, you can then cascade a diode to the DC output to prevent the directional voltage caused by the device damage. Reference: 1, LM7812 Handbook: http://wenku.baidu.com/view/7103d93610661ed9ad51f32b.html?re=view2, XL1509 Manual:/http www.docin.com/p-773783557.html 
[Original]DC-DC output voltage will burn down
