Abstract: | Interface impedance test is a common method for judging whether the product status is normal in aerospace products. In the application of aerospace products, it is generally considered that an abnormal impedance test of an interface chip means that the interface chip has failed. The phenomenon is analyzed that the impedance test of an LVDS interface transmitter chip is abnormal due to static electricity but the function is normal. Based on the failure analysis of components, the location of electrostatic damage is determined as the electrostatic protection circuit inside the chip, and the corresponding circuit model is established to theoretically analyze the phenomenon of electrostatic damage to the chip. The analysis shows that: When the chip is struck by static electricity, an NMOS tube in its electrostatic protection circuit is damaged, but this circuit protects the functional circuit of the chip, and the broken NMOS tube is equivalent to a resistor. As a result, the impedance test is abnormal but the functional circuit of the chip is not damaged, which is the phenomenon of electrostatic soft breakdown. It can be also considered that the chip does not fail after being affected by static electricity, and the related circuits can still work normally. Therefore, the impedance anomaly is not a sufficient condition for chip failure. |