RS-485 High-Speed Performance: ISL3179E vs. Competitors

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Video Transcript

Hello, my name is Randy Pitts, and I'm the marketing manager of the Intersil interface product line. Today I'm going to compare the high-speed performance of the ISL3179E RS-485 transceiver against similar parts from two competitors. This demonstration will show that the Intersil transceiver delivers better signal integrity over a longer distance.

For this comparison we will be running the transceivers at 40Mbps, driving 300ft of double terminated unshielded twisted pair cable. We are using a four-pulse burst test as a figure of merit to determine the acceptable transmission distance for these transceivers. Critical parameters are the differential voltage delivered at the far end of the cable, and the width of the first pulse out of the receiver.

On the left, we have a transmitter board that drives the 300ft of cable being received by the board on the right. On the screen we have the results from the first competitors' transceivers. The yellow trace at the top is the transmitter input. The orange trace below that is the differential signal at the receiver end of the cable.

The blue and pink traces are the transmitter Y and Z signals at the receiver end of the cable, and the green trace is the receiver output signal. The scope display shows the results for the first competitor. The orange cursors indicate the differential voltage of -520mV that is delivered to the receiver. The larger the magnitude of this voltage the better. The scope now shows the receiver first bit pulse width as indicated by the vertical green cursors.

An ideal pulse width would be 25ns which represents a 40Mbps data rate. This device measures only 14.4ns which indicates 10.6ns of pulse width distortion.

We are now showing the results for the second competitor. The orange cursors indicate the differential voltage of -560mV, that is delivered to the receiver. Once again the scope shows the receiver first bit pulse width as indicated by the green cursors. This device measures only 16ns which is 9ns of distortion.

Now let's look at the performance of the Intersil ISL3179E 40Mbps 3.3V transceiver. The Intersil device delivers at least a 20% larger differential voltage of -68mV delivered to the receiver. The receiver first bit pulse width of 25.6ns is only .6ns from the ideal, versus 10.6ns and 9ns from the competitors.

To summarize, the Intersil transceiver delivers 20% larger differential output voltage and less than one-tenth the bit distortion compared to the competition when driving a 300ft cable. For the best high-speed performance over long cables, we recommend Intersil's ISL3179E for 3.3V applications or the ISL3159E for 5V applications.

Thank you for watching.