3.3V to 5V Programmable RS232/RS485/RS422 Serial Transceiver
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Information 3.3V to 5V Programmable RS-232/RS-485/RS-422 Serial Transceiver
Supported Protocols RS232, V.28, RS485, RS422, V.24
Supply Voltage (Nom) (V) 3.3, 5
232 Tx / Rx 3 / 5
485 Tx / Rx 2 / 2
RS-232 Max Data Rate (Mbps) 1
RS-485/RS-422 Max Data Rate (Mbps) 15
HBM ESD (kV) 15
IEC 61000-4-2 Contact (±kV) -
120Ω Termination
VL Pin
232 Full Handshake
Slew Limit Pin
Fault Tolerance (V) -15 to 15
RS-485 Duplex Full
Max ICC (mA) 15
Temperature Range (°C) 0 to 70, -40 to 85
Package TSSOP-28
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The SP337E is a dual mode serial transceiver containing both RS-232 and RS-485 line drivers and receivers. The RS-232 mode provides three drivers and five receivers to support all eight signals commonly used in the DB9 serial port connector (3TX/5RX). In RS-485 mode the device features two independent high speed RS-485/RS-422 transmit and receive channels (2TX/2RX). The default RS-485 configuration is full-duplex, but half-duplex operation can be obtained by tying together the TX and RI pins, and the TXEN and RXEN signals. The SP337 is pin compatible to Exar’s SP334.

The SP337EB features a maximum data rate of 250kbps in RS-232 mode and a maximum data rate of 15Mbps in RS-485. However, the SP337EUfeatures a maximum data rate of 1Mbps in RS-232 mode and a maximum data rate of 15Mbps in RS-485 mode.

The Exar-patented high efficiency charge pumps (5,306,954) deliver true RS-232 driver output voltages from a single power supply from 3.3V to 5V. Charge pump outputs are self-monitoring to minimize power consumption. The SP337E requires only four 0.1μF capacitors for complete functionality.

All RS-485 receivers or transceivers feature high impedance inputs which allow up to 256 transceivers on a single shared bus. When configured in RS-485 mode, each driver may be individually enabled or put into tri-state, simplifying use on shared buses or for bidirectional communication. The RS-485 drivers can be disabled (high-Z output) by the TXEN enable pin. The RS-232 receiver outputs can be disabled by the RXEN enable pin.

All receivers have advanced failsafe protection to prevent oscillation when inputs are un-connected. In RS-232 mode, each receiver input has a 5kΩ pull-down to ground. In RS-485 mode, receivers will default to output logic 1 if inputs are floating, shorted, or open but terminated.

All driver outputs and receiver inputs are protected against ESD strikes up to +/-15,000 volts.

  • 3.3V to 5V Single Supply Operation
  • Robust +/-15kV ESD Protection
    • Human Body Model
  • Max Data Rate of 15Mbps in RS-485/RS-422 and up to 1Mbps in RS-232 Mode (SP337EU)
  • 3 Drivers, 5 Receivers RS-232/V.28
  • 2 Drivers, 2 Receivers RS-485/RS-422
    • Full-Duplex Configuration
    • 1/8th Unit Load, up to 256 receivers on bus
  • RS-485 Advanced Failsafe on Open, Short or Terminated Lines
  • Full Differential Driver Tri-State (Hi-Z) Control
  • Receiver Output Tri-State Control
  • SOICW-28 or TSSOP-28 Package

  • Dual Protocol Serial Ports (RS-232 or RS-485)
  • Industrial Computers
  • Industrial and Process Control Equipment
  • Point-Of-Sales Equipment
  • Networking Equipment
  • HVAC Controls Equipment
  • Building Security Equipment

Documentation & Design Tools

Type Title Version Date File Size
Data Sheets SP337E 3.3V to 5V Programmable RS232/RS485/RS422 Serial Transceiver 2.0.0 July 2021 598.3 KB
Application Notes Advantages of Designing with Multi-Protocol Transceivers Application Note R00 September 2023 2.5 MB
Application Notes DAN-190, MaxLinear UARTs in RS-485 Applications R01 July 2023 2.4 MB
Application Notes RS-232 and RS-485 PCB Layout Application Note R00 December 2022 2.8 MB
Application Notes AN211, SP337 Pinout Recommendation for Single DB-9 Connector 1.0.1 March 2013 193 KB
Application Notes AN212, RS485 Termination Resistor Switch Solution 1.0.0 August 2011 266.1 KB
User Guides & Manuals XR21B1420 Evaluation Board User’s Manual 1B January 2020 1.2 MB
Product Brochures Interface Brochure November 2023 3.7 MB
Schematics & Design Files XR21B1420/1421 Evaluation Board Design Files REV 10 June 2016 386.5 KB
Simulation Models
Package Type Vcc Temp Mode Version File
WSOIC-28 3.3V Commercial RS-232 5
WSOIC 3.3V Commercial RS-232 2
WSOIC 3.3V Commercial RS-485 2
WSOIC 5.0V Commercial RS-232 4
WSOIC 5.0V Commercial RS-485 2
TSSOP 3.3V Commercial RS-232 2
TSSOP 3.3V Commercial RS-485 2
TSSOP 5.0V Commercial RS-232 2
TSSOP 5.0V Commercial RS-485 2
WSOIC 3.3V Industrial RS-232 2
WSOIC 3.3V Industrial RS-485 2
WSOIC 5.0V Industrial RS-232 2
WSOIC 5.0V Industrial RS-485 2
TSSOP 3.3V Industrial RS-232 2
TSSOP 3.3V Industrial RS-485 2
TSSOP 5.0V Industrial RS-232 2
TSSOP 5.0V Industrial RS-485 2
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Quality & RoHS

Part Number RoHS | Exempt RoHS Halogen Free REACH TSCA MSL Rating / Peak Reflow Package
SP337EBEY-L N Y Y Y Y L1 / 260ᵒC TSSOP28
SP337EUEY-L N Y Y Y Y L1 / 260ᵒC TSSOP28
SP337EUEY-L/TR N Y Y Y Y L1 / 260ᵒC TSSOP28
SP337EBEY-L/TR N Y Y Y Y L1 / 260ᵒC TSSOP28

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

Additional Quality Documentation may be available, please Contact Support.

Parts & Purchasing

Part Number Pkg Code Min Temp Max Temp Status Suggested Replacement Buy Now Order Samples PDN
SP337EBEY-L TSSOP28 -40 85 Active Order
SP337EBEY-L/TR TSSOP28 -40 85 Active Order
SP337EUET-L WSOIC28 -40 85 OBS SP338EER1-L
SP337EUEY-L TSSOP28 -40 85 Active Order
SP337EUEY-L/TR TSSOP28 -40 85 Active Order
XR21B1420IL28-0A-EVB Board Active
Show obsolete parts
Part Status Legend
Active - the part is released for sale, standard product.
EOL (End of Life) - the part is no longer being manufactured, there may or may not be inventory still in stock.
CF (Contact Factory) - the part is still active but customers should check with the factory for availability. Longer lead-times may apply.
PRE (Pre-introduction) - the part has not been introduced or the part number is an early version available for sample only.
OBS (Obsolete) - the part is no longer being manufactured and may not be ordered.
NRND (Not Recommended for New Designs) - the part is not recommended for new designs.


Pkg Code Details Quantities Dimensions PDF
  • JEDEC Reference: MO-153
  • MSL Pb-Free: L1 @ 260ºC
  • MSL SnPb Eutectic: n/a
  • ThetaJA: 76ºC/W
  • Bulk Pack Style: Tube
  • Quantity per Bulk Pack: 50
  • Quantity per Reel: 2500
  • Quantity per Tube: 50
  • Quantity per Tray: n/a
  • Reel Size (Dia. x Width x Pitch): 330 x 16 x 8
  • Tape & Reel Unit Orientation: Quadrant 1
  • Dimensions: mm
  • Length: 9.70
  • Width: 4.40
  • Thickness: 1.2
  • Lead Pitch: 0.65
  • JEDEC Reference: MS-013
  • MSL Pb-Free: L3 @ 260ºC
  • MSL SnPb Eutectic: n/a
  • ThetaJA: 58.6ºC/W
  • Bulk Pack Style: Tube
  • Quantity per Bulk Pack: 27
  • Quantity per Reel: 1500
  • Quantity per Tube: 27
  • Quantity per Tray: n/a
  • Reel Size (Dia. x Width x Pitch): 330 x 24 x 12
  • Tape & Reel Unit Orientation: Quadrant 1
  • Dimensions: mm
  • Length: 17.90
  • Width: 7.50
  • Thickness: 2.65
  • Lead Pitch: 1.27


Distribution Date Description File
06/17/2020 Process Change Notification - Refer to PCN for details
06/17/2020 Process Change Notification - Refer to PCN for details
12/12/2018 Product Discontinuation Notice
04/19/2018 Qualification of alternate assembly subcon Greatek using copper wire.
07/11/2017 Product Discontinuation Notification
07/11/2017 Product Discontinuation Notification
05/10/2017 Qualification of alternate assembly subcon, JCET.
02/23/2017 Qualification of alternate assembly subcon, ANST, China.
02/15/2017 Qualification of alternate assembly subcon, ANST.
02/09/2016 Qualification of alternate foundry subcon, Silan.
07/03/2013 Addition of qualified 6 inch wafer processing line in Episil, in addition to the currently qualified 5 inch wafer processing line. Other change (foundry 6 inch wafer qualification).
05/23/2013 Qualified copper wire bonding assembly in addition to currently qualified gold wire bonding assembly in Carsem. Material change.
03/08/2012 Wafer Fabrication Facility Wafer foundry request.
07/30/2010 Process Change. Capacity enhancement.

FAQs & 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.
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Submit a Technical Support Question As a New Question

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)









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. Also refer the RS-485 Cable Lengths vs. Data Signaling Rate Application Note (AN-292).

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.

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.

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.

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.

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How to Design a Multiprotocol System using Only 1 Connector

Industrial networks support multiple serial interfaces such as RS-485 and RS-232.  Using a multiprotocol transceiver enables industrial equipment to support both protocols using only one connector. Enabling both smaller and lower cost equipment designs. This video describes how to design multiprotocol systems using only one connector.