Блог компании Supply TI Voltage References:Shunt Voltage References,Series Voltage Reference

Supply TI Voltage References:Shunt Voltage References,Series Voltage Reference

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Voltage references are core components in electronic systems that provide precise, stable and fixed voltages. They supply accurate voltage references for ADCs/DACs, precision sampling circuits, power supply feedback systems and industrial measurement and control modules; their accuracy, temperature drift, noise and stability directly determine the measurement accuracy and control reliability of the entire system.

I. Core Definitions and Operating Principles

1. Shunt-Type Voltage Reference (Parallel Type)

A shunt-type voltage reference is essentially a programmable precision Zener diode, featuring a two-terminal or three-terminal parallel architecture. Its operating principle is highly similar to that of a Zener diode and requires the use of an external current-limiting resistor. The chip is connected in parallel with the load and dynamically adjusts its own shunt current via an internal feedback loop to absorb excess input voltage and offset voltage fluctuations, thereby maintaining a constant output node voltage.

Core operating logic: When the input voltage fluctuates or the load current changes, the chip automatically adjusts the conduction current to clamp the node voltage at a fixed reference value. The current-limiting resistor serves to divide the voltage and limit the current, ensuring the chip operates within the voltage-regulating range. Its output voltage can be flexibly adjusted via an external voltage-dividing resistor to accommodate multi-step voltage requirements.

2. Series-type voltage reference (sequential type)

The series-type voltage reference features a three-terminal series architecture, with the chip connected in series between the input power supply and the load, eliminating the need for a high-power current-limiting resistor. Relying on an internal high-precision feedback amplification loop, it actively regulates the on-voltage drop of the internal power transistor to offset voltage deviations caused by input voltage fluctuations and changes in load current, thereby continuously outputting a stable and precise reference voltage.

Core operating logic: Closed-loop sampling and correction of the output voltage are performed directly, resulting in extremely low static power consumption and fast load response. The device features built-in voltage-differential regulation control, whilst some high-end models incorporate a shutdown mode to achieve ultra-low standby power consumption, making them suitable for high-precision, low-power applications.

II. Differences in Hardware Architecture

Shunt-type voltage references consist of at least a two-terminal structure. Conventional three-terminal products support voltage regulation but require an external current-limiting resistor to function correctly. Whilst they involve slightly more peripheral components, their architecture is flexible and can accommodate positive, negative and floating reference voltage designs.

Series-type voltage references feature a standard three-terminal architecture (input, output, ground) and require no external current-limiting resistors, resulting in a minimalist peripheral circuit. Some high-end models incorporate enable/disable pins and dual-channel output, allowing direct output of a fixed reference voltage; they are plug-and-play, simplifying circuit design.

III. Typical TI Products

1. Classic Shunt-Type Voltage References

TI’s shunt-type references are characterised by high cost-effectiveness, a wide voltage range and flexible adjustability, making them the mainstream choice for general industrial applications. Key representative models are as follows:

- TL431: An industry-standard classic, featuring a fixed 2.5V reference. The output voltage can be adjusted up to 36V via a voltage-divider resistor, with an initial accuracy of 0.5% and a typical temperature drift of 30 ppm/°C. Extremely low-cost and highly versatile, it is widely used in switch-mode power supply feedback, general-purpose sampling circuits and entry-level instruments.

- ATL431: An upgraded version of the TL431, featuring ultra-low quiescent current, enhanced stability, optimised performance under boundary conditions, and a lower input reference current, which effectively improves voltage output accuracy. It is suited to miniaturised, low-power general-purpose applications and features a more compact package.

- LM4040: A precision shunt reference with selectable fixed output voltages of 2.5 V, 4.096 V and 5 V. It offers better initial accuracy than the standard TL431 and lower temperature drift, making it suitable for mid-range precision sampling and battery monitoring circuits.

2. Classic Series Voltage Reference Products

TI’s series voltage references are characterised by high precision, low temperature drift, low noise and low power consumption, and are tailored for high-end precision measurement and control, industrial automation and high-precision data acquisition applications. Key representative models are as follows:

- REF30xx Series: General-purpose, high-precision series-connected references with fixed outputs of 1.25 V, 2.048 V, 2.5 V, 3.3 V and others. With a quiescent current of only tens of microamperes and a temperature drift as low as 15 ppm/°C, these compact packages are well-suited for battery-powered and portable precision equipment.

- REF50xx Series: Industrial-grade, high-precision models with initial accuracy as low as 0.02 per cent, temperature drift as low as 0.05 ppm/°C, ultra-low output noise and built-in temperature compensation, specifically designed for high-precision ADCs/DACs, smart meters and industrial transmitters.

- REF20xx Series: Ultra-low-power series-connected references with integrated shutdown functionality; standby power consumption is virtually zero; supports dual-channel output; balances accuracy and power consumption; suitable for IoT terminals and low-power industrial measurement and control equipment.

IV. In-depth Analysis of the Advantages and Disadvantages of the Two Product Categories

1. Advantages and Disadvantages of Shunt-Type Voltage References

Key advantages: Firstly, they are low-cost and offer excellent value for money, making them suitable for high-volume, general-purpose products; secondly, they have a wide input voltage tolerance, adapting to a variety of high- and low-voltage power supply scenarios; thirdly, voltage configuration is flexible, enabling positive, negative and floating reference voltages, with extremely strong circuit adaptability; fourthly, they possess inherent current sink and source capabilities, offering strong resistance to transient voltage fluctuations.

Key Drawbacks: An external current-limiting resistor is required, which increases PCB area and power consumption; the continuous heat generation from the resistor affects system energy efficiency; static power consumption is relatively high, making it unsuitable for battery-powered, ultra-low-power devices; accuracy and temperature drift performance are limited, failing to meet the requirements of high-precision metering and high-end measurement and control scenarios; there is no sleep or shutdown mode, meaning it operates continuously throughout, and power consumption cannot be controlled.

2. Advantages and Disadvantages of Series-Connected Voltage References

Core Advantages: Excellent accuracy, temperature drift and noise performance, making them the preferred choice for high-precision reference applications; no external current-limiting resistor is required, resulting in minimal peripheral circuitry and a simpler PCB layout; extremely low quiescent power consumption, with some models supporting shutdown and sleep modes, making them suitable for low-power devices; excellent load regulation and linearity, ensuring exceptional output voltage stability during load fluctuations.

Main drawbacks: Higher cost than shunt-type references, offering poor value for money in cost-sensitive applications; input voltage is subject to a maximum limit and minimum voltage difference, restricting the input voltage range; cannot operate in reverse sink mode, making it impossible to establish floating or negative reference voltages, resulting in slightly reduced flexibility in application suitability.

V. Suitable Applications and Selection Principles

1. Applications for Shunt-Type Voltage References

Suitable for general-purpose, low-cost applications that do not require ultra-high precision, primarily including: voltage regulation feedback circuits in switching power supplies, standard microcontroller sampling systems, battery voltage monitoring, general measurement and control in consumer electronics, entry-level industrial control modules, and general-purpose circuits requiring an adjustable reference voltage. Shunt-type references should be the preferred choice for cost-sensitive projects with non-stringent requirements for temperature drift and accuracy, and where flexible voltage configuration is required.

2. Applications for Series-Type Voltage References

Suitable for high-precision, low-power and high-stability applications, primarily including: high-precision ADC/DAC data acquisition systems, industrial automation transmitters, precision instruments and meters, battery-powered portable devices, low-power IoT terminals, measurement and control systems requiring low temperature drift and low noise, and industrial equipment requiring long-term stable operation. For applications with stringent requirements regarding measurement accuracy, temperature drift and power consumption, a series-type reference must be selected.

3. Summary of Key Selection Criteria

For applications requiring the best value for money, flexible voltage adjustment and universal compatibility, select TI’s shunt-type voltage references (TL431, ATL431, LM4040); for applications requiring high precision, low temperature drift, low noise, low power consumption and high stability, select TI’s series-type voltage references (REF30xx, REF50xx, REF20xx).

VI. Conclusion

TI’s shunt-type and series-type voltage references are not mutually exclusive alternatives, but rather two complementary categories of core products suited to different scenarios. Shunt-type references dominate the general-purpose market due to their flexibility, low cost and broad compatibility, and are the standard choice for industrial and consumer electronics; series-type references are established in high-end precision measurement and control applications due to their high accuracy, low power consumption and high stability, ensuring the precision of system measurement and control.