Overview
| Information | 20Mbps Full-Duplex RS-485 Transceivers with +/-15KV ESD |
|---|---|
| Supported Protocols | RS-422, RS-485 |
| Supply Voltage (Nom) (V) | 5 |
| No. of Tx | 1 |
| No. of Rx | 1 |
| Duplex | Full |
| Data Rate (MAX) (Mbps) | 20 |
| HBM ESD (kV) | 15 |
| IEC 61000-4-2 Contact (±kV) | - |
| Rx Fail-Safe | Standard |
| Multi-Drop Nodes | 32 |
| Transient Tolerance (V) | |
| Fault Tolerance (V) | |
| VL Pin | |
| Temperature Range (°C) | 0 to 70, -40 to 85 |
| Package | NSOIC-14 |
| ICC (Max) (mA) | - |
| Shutdown | ✔ |
| Typ Shutdown Current (µA) | 10 |
| Hot Swap | |
| PROFIBUS (5V) or High Output (3V) |
The SP1490E is a low power differential line driver/receiver meeting RS-485 and RS-422 standards up to 20Mbps. The SP1491E is identical to the SP1490E with the addition of driver and receiver tri- state enable lines. Both products feature ±200mV receiver input sensitivity, over wide common mode range. The SP1490E is available in an 8-pin NSOIC packages for operation over the commercial and industrial temperature ranges. The SP1491E is available in a 14-pin NSOIC packages for operation over the commercial and industrial temperature ranges.
- +5V Only
- Low Power BiCMOS
- Driver/Receiver Enable
- RS-485 and RS-422 Drivers/Receivers
- Pin Compatible with SN75180
- Improved ESD Specifications
- ±15kV Human Body Model
- ±15kV IEC1000-4-2 Air Discharge
Documentation & Design Tools
| Type | Title | Version | Date | File Size |
|---|---|---|---|---|
| Data Sheets | SP1490E/SP1491E Full Duplex RS-485 Transceivers | 1.0.1 | May 2013 | 367.9 KB |
| Application Notes | RS-232 and RS-485 PCB Layout Application Note | R00 | December 2022 | 2.8 MB |
| Application Notes | AN-292, RS-485 Cable Lengths vs Data Signaling Rate | R01 | July 2022 | 2.7 MB |
| Application Notes | ANI-12, RS-485 Isolated Interface | Rev B | September 2017 | 89.5 KB |
| Application Notes | ANI-13, RS-485 and RS-422 Physical Topologies | D | December 2006 | 183.2 KB |
| Product Brochures | Interface Brochure | R01 | June 2024 | 3.6 MB |
Parts & Purchasing
| Part Number | Pkg Code | Min Temp | Max Temp | Status | Suggested Replacement | PDN |
|---|---|---|---|---|---|---|
| SP1491ECN | NSOIC14 | 0 | 70 | OBS | ||
| SP1491ECN-L | NSOIC14 | 0 | 70 | OBS | ||
| SP1491ECN-L/TR | NSOIC14 | 0 | 70 | OBS | ||
| SP1491ECN/TR | NSOIC14 | 0 | 70 | OBS | ||
| SP1491ECP | PDIP14 | 0 | 70 | OBS | ||
| SP1491ECP-L | PDIP14 | 0 | 70 | OBS | ||
| SP1491ECS | PDIP14 | 0 | 70 | OBS | ||
| SP1491EEN | NSOIC14 | -40 | 85 | OBS | ||
| SP1491EEN-L | NSOIC14 | -40 | 85 | OBS | ||
| SP1491EEN-L/TR | NSOIC14 | -40 | 85 | OBS | ||
| SP1491EEN/TR | NSOIC14 | -40 | 85 | OBS | ||
| SP1491EEP | PDIP14 | -40 | 85 | OBS | ||
| SP1491EEP-L | PDIP14 | -40 | 85 | OBS |
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.
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.
Packaging
| Pkg Code | Details | Quantities | Dimensions |
|---|---|---|---|
| NSOIC14 |
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| PDIP14 |
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Notifications
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) |
| 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. Also refer the RS-485 Cable Lengths vs. Data Signaling Rate Application Note (AN-292).
As RS-422/RS-485 uses differential signaling, it is more immune to noise and longer cables and/or high data rates can be used, especially in noisy environments. Also, RS-485 allows for multi-point operation, up to 32 unit loads. Transceivers may use a fraction of a unit load, increasing the number of devices on the bus. For example, the XR33152 receiver input impedance is at least 120 kΩ, which equates to 1/10 of a unit load. Therefore, XR33152 allows more than 320 devices (32 x 10) on the bus.
Fail Safe is an attempt to keep the output of the RS-485 receiver to a known state. Transceivers may have standard fail safe or advanced / enhanced receiver fail safe features. Standard fail safe supports open inputs while enhanced fail safe transceivers such as the SP339 and XR34350 support open input, shorted input and undriven terminated lines without external biasing. See Application Note ANI-22 for more detail.
Figure 1: Standard Failsafe Receiver Sensitivity Range
Figure 2: Standard Failsafe with Open Input
Figure 3: Enhanced Failsafe Receiver Sensitivity Range
Figure 4: Enhanced Failsafe with Open Input
Figure 5: Enhanced Failsafe with Shorted Input
Figure 6: Enhanced Failsafe with Un-driven terminated lines
Yes, this is possible using one RS-485 transceiver. The microcontrollers will have to be addressable and have tri-state outputs. The RS-485 device can be controlled by the host via the DE/RE pin. The micros will have to be in either receiving mode or tri-state mode when the RS-485 transceiver is transmitting data. When the host transmits it will have to send an address to the specific micro. If any micro transmits the transceiver will have to be in receiving mode and all other micros will have to be in receive or tri-state. So the host would have to initiate this sequence by addressing the micro first then switch the transceiver to receive.
The half duplex system would have a bus with one transceiver and multiple microcontrollers all tied to the bus. For 5V systems the SP485 family can be used. For 3V systems the SP3070 family can be used. The require speed will determine the part number. The SP3078 part runs up to speeds of 16Mbps. See the parametric search on https://www.exar.com/products/interface/serial-transceivers/rs485-422 for more options.
Care must be taken to assure the transceiver can drive the multiple micros in RX mode.
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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