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

Added on August 21, 2015
See how Intersil’s ISL3179E 40Mbps transceiver stacks up against similar parts from 2 competitors.

Related Resources

ISL3179E, ISL3180E Datasheet ISL3179E, ISL3180E Datasheet

isl3179e-80e.pdf (741 KB)
Aug 2015

ISL3159E Datasheet ISL3159E Datasheet

isl3159e.pdf (1.32 MB)
Aug 2017

ISL3259E Datasheet ISL3259E Datasheet

isl3259e.pdf (1.19 MB)
Aug 2017

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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 40 megabits per second, driving 300-foot 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 300-foot 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 -520 millivolt 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 25 nano seconds which represents a 40 megabit per second data rate. This device measures only 14.4 nano seconds which indicates 10.6 nano seconds of pulse width distortion.

We are now showing the results for the second competitor. The orange cursors indicate the differential voltage of -560 millivolts, 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 16 nano seconds which is 9 nano seconds of distortion.

Now let's look at the performance of the Intersil ISL3179E 40 megabit per second 3.3 volt transceiver. The Intersil device delivers at least a 20% larger differential voltage of -680 millivolts delivered to the receiver. The receiver first bit pulse width of 25.6 nano seconds is only .6 nano seconds from the ideal, versus 10.6 nano seconds and 9 nano seconds 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 300-foot cable. For the best high speed performance over long cables, we recommend Intersil's ISL3179E for 3.3 volt applications or the ISL3159E for 5 volt applications.

For more information about Intersil's Interface products or to download a datasheet, please visit www.intersil.com/interface. Thank you for watching.