The TL431 is an adjustable shunt voltage reference that offers a guaranteed temperature stability over different operating temperature ranges. It is also designed to operate over a wide range of current range particularly within 1 to 100mA while maintaining a dynamic impedance of 0.22Ω.
In this article you will learn more about how resistors, transistors and other components are implemented in silicon to form the TL431 chip. Ultimately this will give you a deeper understanding of the evolution of voltage reference ICs and the impact of TL431 on modern electronics. Continue reading for more.
Overview of the TL431 Voltage Reference
The TL431 is a programmable precision voltage reference that is mostly utilized in switching power supplies. This is particularly in cases where it can offer feedback that shows whether the output voltage is too low or too high. With the utilization of a bandgap which is a special circuit the TL431 offers stable voltage reference which is maintained at a wide temperature range.
The history of the TL431 dates back to 1978 when it was first introduced to the market. It has since then built a strong reputation by playing a major part in the development of many devices today. For instance it played a key role in the regulation of Apple II power supply and is also now utilized in most ATX power supplies. It is also applied for a wide range of chargers including iPhone chargers.
Other applications of the TL431 can be seen in the MagSafe adapter, laptop adapters, LED drivers, video games, televisions, audio power supplies and minicomputers. A key thing to understand about the TL431 is that it is available in different sizes and shapes. However this component doesn’t gain much attention because it doesn’t look like an IC but like a simple transistor.
Implementation of Components in TL431 Silicon
Because the TL431 is a simple IC it is easy to understand what happens on its layout and this only requires close examination. Continue reading to learn about how resistors, transistors, capacitors and fuses are implemented.
Implementation of Resistors in Silicon
Resistors are a vital component of analog chips like the TL431. They are mostly implemented as a strip of doped silicon. By using varying lengths of resistive materials one can easily obtain different resistances. The key thing to understand is that the resistance is proportional to the length to width ratio.
Another thing to note is that resistors in ICs usually have a poor tolerance. Basically this tolerance can vary 20% across different chips and this is because of the differences in their manufacturing process.
Silicon Fuses to Trim Resistors
Fuses for trimming the resistances is also a key feature of the TL431 which many may not know. When the chips are manufactured these fuses are blown with the aim of adjusting the resistance and increasing the accuracy of the chip. There are also chips with laser trimmed resistors where the laser burns away before the chip is repackaged to offer a higher level of control than the fuse.
Capacitors
There are two capacitors within the TL431 and they are implemented via different mechanisms. For the first capacitor a reverse biased diode is used for its formation. There is also a capacitance at the junction of the reverse biased diode and this is also utilized in forming a capacitor. However it’s worth noting that this type of capacitor has its own limitation particularly in terms of the capacitance which varies with changing voltage due to the junction width changes.
The formation of the second capacitor is achieved via a different mechanism which is more like a conventional capacitor that has two plates. It features a metal plate with N+ silicon below which acts as the second plate. It’s worth noting that the capacitor consumes up to 14% of the die which further indicates that the capacitor uses space inefficiently when integrating circuits.
How the Chips Works
The external operation of the TL431 is straightforward. When the voltage on the reference pin input is higher than 2.5 volts the output transistor conducts and this causes the flow of current between the anode and the cathode pins. For power supply this causes an increase in the flow of current signals for the power control chip thereby triggering the reduction in the power to bring the voltage to a more desirable level. Therefore TL431 is mainly used in power supply to keep output voltage at a stable range.
The chips also have an intriguing internal operation and the most interesting is the temperature compensated bandgap voltage reference. Basically transistors are affected by temperature in different ways and the outputs of the transistors are also combined so that the effects of temperature can be effectively canceled out to form a more stable reference.
It’s worth noting that the voltages from the temperature stabilized bandgap are sent to a comparator with inputs to drive the comparator. Also the output of the comparator goes through a transistor (Q10) before it is sent as output to the Q11 transistor.
Key Takeaway
The TL431 has had a significant impact on modern electronics since its introduction by Texas Instruments in 1977. This three-terminal adjustable shunt voltage regulator has become a staple in various applications due to its versatility and precision.
Key Contributions of the TL431
- Versatility: The TL431 can be used in numerous configurations including power adapters, voltage comparators and current sources. This flexibility makes it a go to component for many design engineers.
- Precision: With an initial reference voltage deviation measured in millivolts the TL431 ensures high accuracy in voltage regulation. This precision is crucial for applications requiring stable and reliable voltage references.
- Size and Integration: The evolution of the TL431 has led to smaller package sizes, such as the ATL431LI which is significantly smaller than typical resistors. This reduction in size allows for more compact and efficient designs particularly in space-constrained applications like LED lighting.
- High Gain Bandwidth: The TL431’s large gain bandwidth facilitates higher frequency switching which is beneficial for applications requiring precise control such as LED dimming.
The TL431’s impact on modern electronics is evident in its widespread use and the continuous development of its derivatives, which offer improved performance and smaller footprints. This evolution highlights the importance of the TL431 in advancing electronic design and innovation.
Is there a specific aspect of the TL431 or its applications that you’re particularly interested in? Find out more in the datasheet.
