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AVCMOS Outputs of CY2CC810 Explained | Cypress Semiconductor

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AVCMOS Outputs of CY2CC810 Explained

Last Updated: December 26, 2011

Will AVCMOS outputs require terminations? Explain Operation.


The CY2CC810 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.

A description of AVCMOS Outputs operation is as follows:

The output driver has a feedback line into the analog drive for the device. This senses the voltage level that the driver is at-- a simple volt meter concept.

The output driver consists multiple drivers tied in parallel except for the drive control.

As the device starts to swing from the ground rail towards the power rail, these are at first all on and slowly begin to shut down as the voltage is in the VOH range. When the voltage gets to the 90% value, a relatively low current driver drives the device through the last 10% of the voltage swing, helping to avoid overshoot. Naturally, if the load is dynamic, the driver becomes more dynamic in nature.

For the falling edge, the logic is reversed and the device tries to prevent overshoot/undershoot at the VOL level.

If there are reflections or noise on the line, the output driver will try to respond to these and may shut down the output early or late due to the bandwidth of the sense and that of the reflection.

The real intent is to have fast edge transitions but to also prevent over and undershoot.

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