3.3V Tolerant inputs, with input of 2.5V on the CY2CC810

Question: In the CY2CC810 datasheet, it states that the input is 3.3V tolerant even when operating at 2.5V, and that it does not require any external series resistors. How can this be?

 

Answer:

The input will be 3.3V tolerant when operating at 2.5V, specified as maximum 5V for Vih in the datasheet. The device has AVCMOS outputs which means they dynamically adjust their output impedance to smooth the output edges and stop any undershoot or overshoot. This means that external source termination resistors will not be necessary to eliminate reflections. The outputs will be capable of driving 2 loads, as long as the length and loads of both traces are identical. With this configuration the outputs will be able to operate up to 160MHz, as specified under the standard load circuit in figure 1 of the datasheet.