الملخص

The Texas Instruments TL431 series voltage references are renowned for their precision and versatility in the realm of electronic circuit design. Introduced in 1977, these components are commonly referred to as adjustable shunt regulators or programmable precision references. They are highly regarded for their ability to maintain stable output voltages, which is crucial in applications such as power management, switching power supplies, and overvoltage protection circuits

. One of the primary features of the TL431 series is its internal temperature-compensated bandgap voltage reference, which ensures reliable performance across a broad temperature range. The TL431 operates by conducting current between its cathode and anode pins when the voltage at the reference pin exceeds 2.5 volts, signaling power supply control chips to stabilize output voltage. This precision and adaptability make the TL431 a popular choice for designers looking to implement efficient and stable voltage regulation in their circuits. Over the years, Texas Instruments has expanded the TL431 series to include several variants such as the TL432, TL431LI, and the broader TL43xx series. Each variant is tailored to meet specific performance criteria and environmental conditions, from consumer electronics to industrial applications. These derivatives offer variations in packaging, temperature ranges, and initial tolerance levels, providing engineers with a range of options to suit their precise needs. Despite their widespread use and reliability, the TL431 series has not been without controversy. Texas Instruments has acknowledged that their initial stability boundary charts were overly optimistic, recommending more conservative design targets to ensure robust performance. This has led to discussions within the engineering community regarding the optimal implementation of these voltage references to achieve the best stability and reliability in various applications.

المواصفات

The Texas Instruments TL431 series of voltage references are precision programmable references with several notable specifications and features. These devices are categorized under various descriptions such as “adjustable shunt regulator,” “programmable precision reference,” “programmable shunt voltage reference,” and “programmable zener” due to their unique functionality

.

الخصائص الكهربائية

The TL431 operates straightforwardly by conducting current between the cathode and anode pins when the voltage on the ref pin input exceeds 2.5 volts

. This conduction signals the power supply control chip to reduce power, thus stabilizing the output voltage. The chip’s internal operation includes a temperature-compensated bandgap voltage reference, utilizing transistors with different emitter areas to balance temperature effects.

الخصائص الفيزيائية

The TL431 has a single layer of metal that connects its internal components, with the physical dimensions of the die impacting its functional attributes. The chip is connected through three pins labeled “ref,” “anode,” and “cathode”

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Packaging and Variants

Texas Instruments offers the TL431 in different packaging options to cater to various application needs. The TL431 datasheet provides detailed electrical characteristics and absolute maximum ratings, which include the allowable ranges for supply voltage, input voltage, and operating temperature

. The TL431 series also includes variants such as TL432, which shares similar precision and programmability features.

Example Applications

These voltage references are widely used in power management applications, where they help maintain stable output voltages. Their precision and programmability make them suitable for use in adjustable shunt regulators, switching power supplies, and overvoltage protection circuits

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Operation

The TL431 is a three-terminal adjustable shunt regulator with a specified thermal stability over applicable automotive, commercial, and military temperature ranges. It operates in a manner similar to a Zener diode but with the additional advantage of being programmable. The pinout for the TL431 is straightforward: the center pin is the Anode (A), the left pin is the Reference (R), and the right pin is the Cathode (K)

. Internally, the TL431 contains a precision reference voltage source, a comparator, and an output transistor . When the voltage at the reference pin exceeds 2.5V, the output transistor turns on, allowing current to flow between the cathode and anode pins . This behavior makes the TL431 useful in a variety of applications including shunt regulators, precision current limiters, and as a component in switching power supplies and battery chargers . A simplified block diagram reveals that the TL431 has higher efficiency than a standard Zener diode, owing to its internal components such as a comparator Op-amp, reference voltage, and transistors . It provides a programmable output voltage up to 40V with a guaranteed 0.5% reference voltage tolerance. Other features include low dynamic output impedance, a cathode current range from 1mA to 150mA, and a low temperature coefficient of 50PPM/°C, ensuring stable operation across a wide temperature range . In practical applications, the TL431 can be configured in a basic shunt voltage regulator circuit similar to a Zener diode regulator, where the resistor (R) is connected to the cathode (K). This setup allows the TL431 to maintain a stable output voltage, with low output noise voltage and fast turn-on response times . Moreover, the TL431 is commonly found in switching power supplies and other digital electronics due to its versatility and reliability. For higher current requirements, the TL431 can be paired with a series pass transistor to convert a shunt regulator into a series regulator, thereby increasing the current capacity significantly . This adaptability and wide range of applications highlight the TL431’s role in modern electronic design.

Variants

Since its introduction in 1977 by Texas Instruments, the TL431 series has seen the development of numerous variants and derivatives, each tailored to meet specific performance criteria and application requirements. While the original TL431 remains in production, its derivatives such as the TLV431, TL432, ATL431, KA431, LM431, and TS431 have emerged to address different needs in precision, speed, and packaging

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TL432

The TL432 is essentially an electrically equivalent variant of the TL431 but is available in surface-mount packages only, featuring a different pinout. This variant provides the same reference voltage and operational characteristics, allowing for a more compact design suitable for modern PCB layouts

.

TL431LI

The TL431LI is another important derivative offered in two grades with initial tolerances of 0.5% and 1% at 25°C for the B and A grades, respectively. This variant is noted for its low output drift versus temperature, ensuring excellent stability over a broad temperature range, from –40°C to 125°C

.

TL43xx Series

The broader TL43xx series, including TL43xxC, TL43xxI, and TL43xxQ devices, are characterized for different operating temperature ranges. The TL43xxC is designed for 0°C to 70°C, the TL43xxI for –40°C to 85°C, and the TL43xxQ for –40°C to 125°C. These variants cater to different environmental conditions, making them suitable for a wide range of applications from consumer electronics to industrial equipment

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Clones and Alternatives

In addition to the official variants by Texas Instruments, the market is flooded with clones and alternative versions like the 142ЕН19, which are functionally similar but may differ in die size, layout, and specific performance metrics such as minimal operating currents and safe operating areas

. Each of these variants and clones offers a unique set of features that can be leveraged to optimize electronic designs for specific applications, whether it’s in power supplies, battery chargers, or voltage monitors. By understanding the nuances of each derivative, designers can select the most appropriate component to achieve the desired balance of precision, reliability, and efficiency .

تصميم الدوائر

The Texas Instruments TL431 series voltage references are versatile components often used in a variety of circuit designs. The internal circuitry of the TL431 includes an NPN transistor at the output biased from an op-amp with a precise 2.5V voltage reference

. This precise reference voltage is fundamental to its use in many applications such as voltage comparator circuits, battery chargers and monitors, solar applications, and switching supply circuits.

Shunt Regulator

The TL431 can be configured as a shunt regulator, capable of outputting voltages between 2.5V and 36V by using just two resistors across the specified pinouts of the device

. The device can be used as a typical shunt regulator as shown in the block diagram. In this configuration, R1 is a variable resistor that adjusts the output voltage, and the series resistor at the supply positive input can be calculated using Ohm’s law: ( R = \frac{V_i}{I} = \frac{V_i}{0.1} ), where ( V_i ) is the supply input and must be below 35V.

Voltage Detector Circuit

A simple application of the TL431 is in a 2.5V voltage detector circuit. This setup involves a voltage divider formed by resistors R1 and VR1. When the voltage at the reference (REF) terminal exceeds 2.5V, the current flows from the cathode (K) to the anode (A) of the IC, similarly to how a Zener diode operates

. This principle can be used to determine whether a pulled IC from an old circuit board is still functional, as the simplest circuit setup can indicate the operational status based on the LED behavior.

Precision Reference Voltage Source

The TL431’s precision reference voltage of 2.5V is utilized in various high-precision applications. For instance, it can act as a precision high-current series regulator or a high-current shunt regulator. The reference voltage remains stable over a wide temperature range due to its temperature-compensated design, ensuring reliable operation in various environmental conditions

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Switching Power Supply

In switching power supply designs, the TL431 can be part of the feedback loop to regulate the output voltage precisely. When the input voltage passes the set feedback voltage limit, it triggers the TL431, turning on the thyristor to generate a pulsating current that can blow a fuse to protect the circuit

. This mechanism ensures that the voltage protection point equals ( (1 + \frac{R1}{R2})V_{ref} ), providing robust overvoltage protection.

Controllable Shunt

The TL431 also features controllable shunt characteristics, allowing small voltage changes at the REF terminal to significantly impact the cathode and anode currents. This feature makes it useful for controlling indicator lights, relays, or directly driving audio loads

. The controllable shunt functionality extends the versatility of the TL431 in applications requiring precise current control.

المقارنات

Despite its popularity, the TL431 series voltage reference has several competitors and different grades that may cater to specific requirements. The TL431, TL431AIDR, and TL431BIDR share the same internal structure and materials but differ in their specifications and testing grades. This differentiation allows for a variety of applications depending on precision and stability requirements

. Texas Instruments has admitted that their stability boundary charts for the TL431 are overly optimistic, suggesting robust designs should target a minimum of a 30-degree phase margin instead of the zero phase margin they originally described. This is achieved by introducing a series resistance between the cathode and load capacitance, which cancels out unwanted phase lag caused by load capacitance alone. Moreover, the precision reference voltage circuit utilizing the TL431 provides better temperature stability and higher output current compared to other references. To prevent self-excitation in capacitive loads, careful consideration of the CL value is necessary. This enhances the TL431’s performance in various applications, including isolated power supplies and adjustable regulated power supplies. Additionally, the TL431 is praised for its simple implementation in circuits like overvoltage protection, voltage monitoring, and voltage detection. These applications leverage the TL431’s internal characteristics, such as its onboard error amplifier and stable reference voltage, to deliver reliable and efficient performance in both digital and analog circuits.

الموثوقية

Reliability is a critical aspect when designing circuits using the Texas Instruments TL431 series voltage references. Ensuring the accuracy of the TL431 calculator’s calculations by simulating and testing the circuit in real-world conditions is paramount. Comparing the simulation results with actual test outcomes allows for validation of the TL431’s performance and the accuracy of calculated values. This step helps in making necessary adjustments before finalizing the design, ensuring the desired output voltage and performance are achieved

. Texas Instruments acknowledges that their stability boundary charts for the TL431 may be overly optimistic. For robust designs, targeting at least a 30-degree phase margin is recommended. Practical applications often involve inserting a series resistance between the cathode and load capacitance, which increases the Equivalent Series Resistance (ESR) and suppresses unwanted oscillations. This method introduces a low-frequency zero, cancelling much of the unwanted phase lag caused by load capacitance alone. Moreover, the TL431’s performance can be evaluated by measuring the output voltage stability using specific test circuits. Adjusting the power supply voltage and monitoring changes in the TL431’s output helps determine its functionality under varying conditions. Proper adjustment and testing can identify whether the TL431 maintains its normal operating states, ensuring reliability in voltage regulation. The TL431’s reliability is further emphasized by the differences in grades and testing processes. Questions regarding the internal structure and material consistency across different grades, such as TL431AIDR and TL431BIDR, highlight the importance of understanding specification limits and test processes. This ensures that the chosen grade meets the reliability requirements for specific applications.

Industry Standards

Texas Instruments has established itself as a key player in the semiconductor industry, with a strong focus on adhering to industry standards to ensure the reliability and quality of its products. The company designs, manufactures, tests, and sells analog and embedded semiconductors, catering to diverse markets such as industrial, automotive, personal electronics, communications equipment, and enterprise systems

. The adherence to stringent industry standards is critical in these sectors, where performance and reliability are paramount. In 1992, Texas Instruments won the prestigious Malcolm Baldrige National Quality Award for manufacturing, which underscored its commitment to quality standards. This accolade prompted the company to adopt the Baldrige criteria as its quality benchmarks, further cementing its dedication to industry excellence. This focus on quality not only enhanced their reputation but also led to vital contracts with major corporations like Sony Corporation, General Motors Corporation, and L.M. Ericsson, highlighting the importance of industry standards in securing and maintaining business relationships. Texas Instruments’ manufacturing prowess is demonstrated through its 15 manufacturing sites worldwide, which reliably deliver high-quality products to meet customer needs. This global footprint ensures that the company can adhere to and often exceed industry standards on a consistent basis, thereby supporting growth and innovation. Additionally, Texas Instruments’ technological advancements, such as the introduction of the eXpressDSP Real-time Software technology in 1999, showcase their commitment to developing products that meet evolving industry requirements. The company’s ability to innovate while maintaining rigorous quality standards has been a cornerstone of its success and industry leadership.

الموارد

Texas Instruments (TI) offers a range of resources to help users make the most of their TL431 series voltage references.

Product Selection

Utilize TI’s PRT+ tool to identify the ideal TL431 product for your specific application with maximum efficiency

. This tool aids in matching your technical requirements with the appropriate component, ensuring optimal performance and cost-effectiveness.

Documentation

For detailed technical information, TI provides extensive datasheets, application notes, and white papers

. These documents contain critical data, including specifications, pin configurations, performance charts, and application guidelines, which are invaluable for both design and troubleshooting purposes.

Sustainability Report

TI is committed to sustainability and energy efficiency, as detailed in their Annual Sustainability Report 2023

. This report outlines TI’s efforts concerning environmental, social, and governance initiatives, reflecting the company’s dedication to making a positive impact through its technology and products.

Sales Support

For inquiries about products and services, or for assistance with design, TI’s sales support team is available to provide expert advice and solutions

. Engaging with the sales team can help address specific application challenges and provide tailored recommendations.

Career Opportunities

TI offers opportunities for individuals looking to transform their future by joining a team focused on cutting-edge intelligent technologies

. By becoming part of TI, employees contribute to shaping innovative solutions that drive the industry forward.

Community and Innovation

TI thrives by fostering an inclusive environment that encourages innovation and respect for diverse perspectives

. The company’s culture promotes curiosity and determination, essential traits for overcoming technical barriers and developing competitive products. For further information and access to these resources, users can visit TI’s official website and navigate through the provided links to the respective tools and documents.