SP331

Documentation

• Datasheet

  • Programmable Dual RS-232/RS-485 Transceiver

• Application Notes

  • ANI-16, Design Guide for Multi-Protocol Serial Ports

• Manuals

  • Evaluation Board User’s Manual

• Product Brochure

  • Interface Brochure

• Product FAQs

  • SP331 FAQ

Application

Packaging

Parts & Purchasing

Quality & Environmental Data

Click on the links above to download the Certificate of Non-Use of Hazardous Substances.

Support

Search our list of FAQs for answers to common technical questions.
For material content, environmental, quality and reliability questions review the Quality tab or visit our Quality page.
For ordering information and general customer service visit our Contact Us page.

Frequently Asked Questions

What is the maximum cable length and data rate for RS-232 and RS-485 / RS-422?

For RS-232 it is 50 feet (15 meters), or the cable length equal to a capacitance of 2500 pF, at a maximum transmission rate of 19.2kbps. When we reduce the baud rate, it allows for longer cable length. For Example:

 

Baud Rate (bps)	Maximum RS-232 Cable Length (ft)
19200	50
9600	500
4800	1000
2400	3000

 

For RS-485 / RS-422 the data rate can exceed 10Mbps depending on the cable length. A cable length of 15 meters (50 feet) will do a maximum of 10Mbps. A cable length of 1200 meters (4000 feet) will do a maximum of 90kbps over 24 AWG gauge twisted pair cable (with 10 pF/ft). Refer to Annex A TIA/EIA-422-B.

 

 

Does the SP331, SP332 and SP334 have >2kV ESD protection? Their datasheets do not mention it.

Yes, the SP331, SP332 and SP334 exceed ±2kV ESD HBM on all pins.  Some interface products have enhanced versions that exceed ±15kV, which applies to the bus data lines.  The parametric search contains ESD information and it is a selection field https://www.exar.com/products/interface/serial-transceivers/multiprotocol/dual-protocol .

How can I find out if the status of a part number is EOL / obsolete or active?

The best way to determine this is to go to maxlinear.com and type the part into the search function. At or near the top of the results you should see something that looks like:

 

 

 

In this example, we looked for XRA1201. Click on part number header or on the link at the bottom of the result.  This brings you to the product page. For example:

 

 

 

Click on Parts & Purchasing, highlighted with the blue arrow above. The screen changes to:

 

 

 

Notice the status column and the “Show obsolete parts” link.  A legend tells you the definition of the different statuses. Click on the “Show obsolete parts” link to see EOL or OBS part numbers along with the Active part numbers, the legend still present:

 

 

 

Another method to find out if a part is OBS or EOL is to click on SUPPORT at the top:

 

 

 

And then Product Change Notifications:

 

  

 

Type the part into the search, and click on one of the part numbers from the drop down menu. Then you can look for the Product Discontinuation Notice, which generally is at the top of the list, for example:

 

 

 

If you see this, it tells you that this particular orderable part has been discontinued and when the last order date is, or was. If you click on the file, then you can view the notice we sent about this if you purchased the part in the recent past. It may also advise of a replacement part. When an orderable part first becomes discontinued, Product Discontinuation Notices are sent are sent to those who have purchased the parts in the recent past, if purchased directly, with a dated opportunity to place a last order.

Does the SP331 support both a 2-wire and a 4-wire RS-485 topology?

The Modes are described on page 8 and Page 11 of the datasheet. Using decimal equivalent; modes 12, 13, 14, can be used for RS485 in either full or half duplex.

Referring to the function table on page 8, modes 12 and 13 are used for half duplex. T1 turns on and off for transmit and receive modes. These same bus lines can be used for the full duplex mode as the transmitter but the receiver is hard wired in a loop back configuration so R3 has to be used as the full-duplex receiver.

If preferred, T3 and R3 can be used as a separate full duplex channel but this requires two more bus lines.

What is the driving capacity of the SP331 and what is the number of slaves that can be multidropped on the RS 485 side?

The SP331 configured for RS485 mode operate as standard RS485 drivers and 1-Unit Load receivers. The drivers can therefore support up to 32 unit loads coexisting on a shared multidrop RS485 bus. If the other nodes on the bus are less than 1-UL a piece then more nodes can be supported. If a biasing supply or other loads are added to the bus then total number of nodes would be decreased.

How much ESD voltage could a part see in normal use?

ESD is caused by static electricity. In order for an ESD event to occur there must be a buildup of static charge. Very high charge levels are actually quite rare. In a normal factory environment, taking basic ESD precautions (grounding-straps, anti-static smocks, ionizers, humidity control, etc.) static levels can be kept below a few tens of volts. In an uncontrolled environment, like an office, static levels rarely get above 2000 volts. Under some worstcase conditions (wearing synthetic fabrics, rubbing against synthetic upholstered furniture, extremely low humidity)

levels can go as high as 12 to 15 thousand volts. Actually to get to 15000 volts or higher you would need to be in an uncomfortably dry environment (humidity below 10%) otherwise static charge will naturally dissipate through corona discharge. It would definitely be considered a “bad hair day.” Humans can generally feel a static shock only above 3000 volts. A discharge greater than 4000 volts can cause an audible “pop.” But repeated lower level discharges can be imperceptible and still may have a cumulative damaging effect on sensitive ICs. All ICs, even those with robust protection, can be damaged if they are hit hard enough or often enough.

Some RS-485 transceiver part numbers look similar to each other but they have an “E” in the part number. Others do not. What does the E mean?

Actually the letter “E” could have two different meanings, depending on where it is in the part number. Most of our interface devices are available in different temperature grades. Commercial temperature (0 to 70C) has a “C” after the numeric part number. Industrial-extended temperature (-40 to +85C) use the letter E. So for example SP485CN is commercial and SP485EN is industrial. The second letter indicates the package type, in this case N for narrow-SOIC. Another E in the suffix indicates that this device has enhanced ESD protection, typically of ±15000Volts on the interface pins. Devices that do not have the enhanced ESD still contain built-in ESD protection of at least ±2000Volts. For example the SP485ECN is ESD rated up to ±15kV, and the SP485CN is rated for ±2kV HBM.

Are your parts 100% tested for ESD?

ESD tests are “destructive tests.” The part is tested until it suffers damage. Therefore parts cannot be 100% tested in production, instead a sample of parts are characterized during the product qualification. The test procedure consists of “zapping” pins with a given voltage using the appropriate model and then running the part through electrical tests to check for functionality or performance degradation.

Why are some pins protected to higher ESD levels than others?

Most ICs in a typical system are at greatest risk of ESD damage in the factory when the PCB is assembled and the system is being built. After the system is put together they are soldered onto the PCB and shielded within a metal or plastic system enclosure. Interface ICs are designed to attach to an external connector that could be exposed to ESD when a cable is plugged in or when a person or object touches the connector. These interface pins are most likely to see ESD exposure and therefore benefit from additional protection.

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