ESD Protection Diodes, VGA Port Companion Circuit

The PACVGA105 incorporates 7 channels of ESD protection for signal lines commonly found in a VGA port for PCs. ESD protection is implemented with current steering diodes designed to safely handle the high peak surge currents associated with the IEC-61000-4-2 Level-4 ESD Protection Standard (±8kV contact discharge). When the channels are subjected to an electrostatic discharge, the ESD current pulse is diverted via the protection diodes into the positive supply rails or ground where they may be safely dissipated. The upper ESD diodes for the R, G and B channels are connected to a separate supply rail (VRGB) to facilitate interfacing to graphics controller ICs with low voltage supplies. The remaining channels are connected to the main 5V rail (VCC). The lower diodes for the R, G and B channels are also connected to a dedicated ground pin (GNDA) to minimize crosstalk due to common ground impedance. Two non-inverting buffers are also included in this IC for buffering the HSYNC and VSYNC signals from the graphics controller IC. These buffers will accept TTL input levels and convert them to CMOS output levels that swing between GND and VCC. These drivers have a nominal 60Ω output impedance to match the characteristic impedance of the HSYNC and VSYNC lines of the video cables typically used. The inputs of these drivers also have high impedance pull-ups (50kW nom.) pulling up to the VAUX rail. In addition, the DDCCLOCK and DDCDATA channels have 1.8kΩ resistors pulling these inputs up to the main 5V (VCC) rail.