In the world of industrial interface ICs, part numbers can be deceiving. Seeing "SN7517...", many engineers instinctively reach for their RS-485 design notes (thinking of the famous SN75176).
Stop right there.
The Texas Instruments SN751701PSR is not an RS-485 chip. It is a dedicated, compact RS-232 Line Driver and Receiver.
Designed to replace the bulky multi-chip solutions of the 1980s (like the SN75188 and SN75189), the SN751701 packs a full UART-to-Serial interface into a tiny 8-pin package. However, it has specific power requirements that catch modern designers off guard.
This guide clarifies exactly what this chip does and how to use it correctly.
Table of Contents
- 1. Decoding the Part Number
- 2. RS-232 vs. RS-485: The Critical Distinction
- 3. Technical Specs: No Charge Pump?
- 4. Hardware Considerations: The "PSR" Package
- 5. Conclusion
1. Decoding the Part Number
TI part numbers tell a precise story about functionality and packaging.
| Segment | Code | Meaning |
|---|---|---|
| SN75 | Series | Commercial Temperature ($0^\circ C$ to $70^\circ C$). (SN55 is Military). |
| 1701 | Device | Line Driver/Receiver. (Single Channel). |
| P | Base Pkg | PDIP-8. (Through-hole version). |
| SR | Mount | SOP-8 (Small Outline Package) + Tape & Reel. |
Identity: This is a surface-mount chip containing 1 Driver (TTL to RS-232) and 1 Receiver (RS-232 to TTL).
2. RS-232 vs. RS-485: The Critical Distinction
This is the most common mistake when ordering parts.
- SN75176 (RS-485): Uses Differential Signaling (Data+, Data-). Logic levels are 0V to 5V. Used for long-distance, multi-point industrial buses.
- SN751701 (RS-232): Uses Single-Ended Signaling (Tx, Rx, GND). Logic levels swing from +12V to -12V. Used for point-to-point connections (e.g., PC COM port to CNC machine).
Warning: If you connect an SN751701 to an RS-485 bus, the high voltage swings (±15V) could destroy standard 5V transceivers.
3. Technical Specs: No Charge Pump?
Modern RS-232 chips (like the MAX232) are famous for generating their own high voltages from a single 5V battery using capacitors ("Charge Pumps").
The SN751701 is old-school. It does not have an internal charge pump.
- Power Requirement: You must supply the high voltages externally.
- $V_{CC+}$: Typically +9V to +15V.
- $V_{CC-}$: Typically -9V to -15V.
- Why use it? If your system already has these rails (e.g., a desktop PC power supply or an industrial control cabinet), the SN751701 is much cheaper, smaller, and quieter (no switching noise) than a MAX232.
4. Hardware Considerations: The "PSR" Package
The SN751701PSR comes in the SOP-8 (PS) package.
- Dimensions: 6.2mm x 7.8mm (including pins).
- Pinout:
- Pin 1 ($V_{CC-}$): Negative Supply (e.g., -12V).
- Pin 2 (RA): Receiver Output (To MCU/TTL).
- Pin 3 (DY): Driver Output (To RS-232 Connector).
- Pin 8 ($V_{CC+}$): Positive Supply (e.g., +12V).
Design Tip: Ensure you have bypass capacitors (0.1µF) on both VCC+ and VCC- pins close to the chip to prevent oscillation.
5. Conclusion
The Texas Instruments SN751701PSR is a specialized tool for specific jobs. It is not a universal transceiver, but for legacy repair or systems with existing dual-rail power supplies, it offers the most robust and cost-effective way to implement a true RS-232 interface. Just remember: feed it the right voltage, and don't call it RS-485.
Sourcing TI Interface ICs Need to repair a legacy serial port? Visit Aichiplink.com to check stock for the SN751701PSR and other TI connectivity solutions.
Written by Jack Elliott from AIChipLink.
AIChipLink, one of the fastest-growing global independent electronic components distributors in the world, offers millions of products from thousands of manufacturers, and many of our in-stock parts is available to ship same day.
We mainly source and distribute integrated circuit (IC) products of brands such as Broadcom, Microchip, Texas Instruments, Infineon, NXP, Analog Devices, Qualcomm, Intel, etc., which are widely used in communication & network, telecom, industrial control, new energy and automotive electronics.
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Frequently Asked Questions
1: What is SN751701PSR used for?
It is an RS-232 line driver and receiver used for point-to-point serial communication.
2: Is SN751701PSR an RS-485 transceiver?
No. It is RS-232, not RS-485, and is not compatible with differential buses.
3: Does SN751701PSR have a built-in charge pump?
No. It requires external positive and negative supply voltages (typically ±12V).
4: What package does SN751701PSR use?
It comes in an SOP-8 (PSR) surface-mount package.
5: What applications commonly use SN751701PSR?
Legacy industrial equipment, CNC machines, instrumentation, and older RS-232 serial ports.
