ZQ Pin of QDR Devices

Question: What is the purpose of the ZQ pin on QDR devices?



Response: In order to provide impedance matching from device to trace, many customers use series or parallel termination. However, termination requires the use of resistors on multiple I/Os, which presents a problem with power dissipation. To rectify this problem, the ZQ pin can be used to provide impedance matching to the trace. Internal circuitry configures the output buffer to adjust to the impedance of the trace. With this method, a single resistor with a value of 5 times the trace impedance can be connected to the ZQ pin, instead of a resistor for each I/O.