Overview
| Information | Intelligent +3.0V to +5.5V RS-232 Transceivers |
|---|---|
| Supply Voltage (Nom) (V) | 3.3, 5 |
| No. of Tx | 5 |
| No. of Rx | 3 |
| Data Rate (kbps) | 250 |
| HBM ESD (kV) | 15 |
| IEC 61000-4-2 Contact (±kV) | 8 |
| Int. Charge Pump | ✔ |
| No. of Ext Caps | 4 |
| Nom Cap Value (µF) | 0.1 |
| Shutdown | ✔ |
| Internal Caps | |
| TTL Tri-State | |
| Auto On-Line | |
| VL Pin | |
| Temperature Range (°C) | 0 to 70, -40 to 85 |
| Package | TSSOP-24 |
The SP3249E device is an RS-232 transceiver solution intended for
portable or hand-held applications such as notebook and palmtop
computers. The SP3249E uses an internal high-efficiency, charge-pump
power supply that requires only 0.1μF capacitors in 3.3V operation. This
charge pump and MaxLinear's driver architecture allow the SP3249E device to
deliver compliant RS-232 performance from a single power supply ranging
from +3.0V to +5.0V. The SP3249E is a 5-driver/3-receiver device, ideal
for laptop/notebook computer and PDA applications.
- Meets true EIA/TIA-232-F Standards from a +3.0V to +5.5V power supply
- Interoperable with EIA/TIA-232 and adheres to EIA/TIA-562 down to a +2.7V power source
- Minimum 250Kbps data rate under load
- Regulated Charge Pump Yields Stable RS-232 Outputs Regardless of VCC Variations
- Enhanced ESD Specifications:
- ±15KV Human Body Model
- ±15KV IEC1000-4-2 Air Discharge
- ±8KV IEC1000-4-2 Contact Discharge
Documentation & Design Tools
| Type | Title | Version | Date | File Size |
|---|---|---|---|---|
| Data Sheets | SP3249E Intelligent +3.0V to +5.5V RS-232 Transceiver | 1.0.0 | January 2011 | 688.4 KB |
| Application Notes | RS-232 and RS-485 PCB Layout Application Note | R00 | December 2022 | 2.8 MB |
| Application Notes | ANI-10, Charge Pump Capacitor Selection Guide for 3V RS-232 Products | B | December 2006 | 71.8 KB |
| Application Notes | ANI-19, Selecting Charge Pump Capacitors for Serial RS-232 Transceivers | D | July 2006 | 386.8 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 |
|---|---|---|---|---|---|---|
| SP3249ECA | SSOP24 | 0 | 70 | OBS | ||
| SP3249ECA-L | SSOP24 | 0 | 70 | OBS | ||
| SP3249ECA-L/TR | SSOP24 | 0 | 70 | OBS | ||
| SP3249ECA/TR | SSOP24 | 0 | 70 | OBS | ||
| SP3249ECY | TSSOP24 | 0 | 70 | OBS | ||
| SP3249ECY-L | TSSOP24 | 0 | 70 | OBS | ||
| SP3249ECY-L/TR | TSSOP24 | 0 | 70 | OBS | ||
| SP3249ECY/TR | TSSOP24 | 0 | 70 | OBS | ||
| SP3249EEA | SSOP24 | -40 | 85 | OBS | ||
| SP3249EEA-L | SSOP24 | -40 | 85 | OBS | ||
| SP3249EEA-L/TR | SSOP24 | -40 | 85 | OBS | ||
| SP3249EEA/TR | SSOP24 | -40 | 85 | OBS | ||
| SP3249EEY | TSSOP24 | -40 | 85 | OBS | ||
| SP3249EEY-L | TSSOP24 | -40 | 85 | OBS | ||
| SP3249EEY-L/TR | TSSOP24 | -40 | 85 | OBS | ||
| SP3249EEY/TR | TSSOP24 | -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 |
|---|---|---|---|
| SSOP24 |
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| TSSOP24 |
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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.
For ordering information and general customer service visit our Contact Us page.
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).
RS-232 uses both positive and negative voltages for signaling. The RS-232 driver needs a charge pump circuit to generate these signal voltages from a single Vcc supply. Four capacitors are needed to generate the positive (V+ or Vdd) and negative (V- or Vss) voltages.
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.
RS232 is the most widely implemented serial interface in the world. It is commonly installed as the serial port (9 pin or 25 pin) on PCs and has become ubiquitous on literally thousands of other applications. See below for comparisons.
Even though RS232 is a very old standard (first standardized in 1962) it is still popular because it is:
- simple, no software stack required, can be used to bring-up microcontrollers or load firmware on a “bare” system
- inexpensive, standard products exist from multiple vendors
- widely understood, support is already built in to most microcontrollers, the basics of serial communication are in most of the textbooks
- performance is adequate for many applications, simple data transfer, text or console ports, diagnostics, peripheral connectivity, etc.
However RS232 does have some limitations:
- It is slow by modern standards. Typical data rates are 1200 baud, 9600 baud, 115.2kbaud. High data rate RS232 devices are available up to 1Mbps. Faster speeds are uncommon.
- Signals swing to both positive and negative voltage. This requires an onboard charge pump to generate signals from a single power-supply chip or else multiple positive and negative supply rails.
- High pin-count per function. All signals are unidirectional and the charge pump requires several pins and external capacitors. So small footprint is difficult to achieve. Cables and connectors use more pins and wires than most modern serial protocols.
- Point-to-point only. Signals go from one driver to one receiver. RS232 does not support bi-directional signals or multiple drivers or receivers.
- Limited distance. RS232 uses single-ended signals which makes it difficult to support long cables. Typical RS232 cables are only about 10 meter or less. High speed (1Mbps) are typically less than 1 meter. The wide driver signal swing makes crosstalk a problem. Unbalanced signals with a shared ground reference are less able to withstand ground shifts between driver and receiver.
- Comparatively high power consumption. The wide signal swing takes quite a bit of power. By the RS232, signals idle at mark-state and receivers have typical 5kΩ impedance to ground, therefore drivers are constantly sourcing current even while idle. Many later RS232 transceivers’ feature shutdown modes or automatic power saving features (such as Auto On-Line, Auto On-Line Plus, Intelligent charge pumps, etc.). However some of the most commoditized devices lack any shutdown function.
RS485 overcomes most of the limitations of RS232 and is an excellent complement to RS232.
- RS485 uses differential signaling and is capable of much higher data rates (up to 20Mbit/sec)
- Differential signals also allow RS485 to communicate over 1200 meter cable lengths. Longer runs are possible with some careful system optimization.
- Bi-directional and multi-drop operation. RS485 can be used to build multidrop networks with many transmitters and many receivers.
- Balanced differential signalling also makes RS485 highly immune to noise. On twisted-pair cables a noise signal will couple equally to both wires in the pair and be ignored by the differential receiver.
RS485 is found mainly in industrial, telecom and commercial applications and is not as widespread in the consumer
or PC world. Therefore it is not seen as often as RS232.
Also the RS485 protocol standard defines only the electrical characteristics of the interface. The physical and logical implementations are left up to the user. Different connectors, different methods for bus-arbitration and data framing all exist under a wide variety of implementations. RS485 has also been used as the foundation for many proprietary or semi-proprietary standards. Therefore interoperability between RS485 based interfaces is not always as simple as with RS232.
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.
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