feature

The TL431 and TL432 devices are three terminal 25°C reference voltage adjustable shunt regulators with specified thermal – suitable for automotive, commercial and

–1% (Class A) military temperature range. The output voltage can be set to any value between Vref – 2% (standard grade) (approximately 2.5 V) and 36 V with two external resistors. These adjustable output voltage: Vref to 36 V devices have a typical output impedance of 0.2Ω.

The active output circuit provides very sensitive turn-on typical temperature drift (TL431B) characteristics when operating over a temperature range of -40°C to 125°C, making these devices excellent replacements for Zener diodes in many applications,

– 6 mV (C temp) such as on-board regulation, adjustable power – 14 mV (I temp, Q temp) power supplies and switching power supplies. TL432

The low output noise device has the exact same functionality and electrical specifications as the TL431 device, but has a typical output impedance of 0.2Ω with different pinouts for DBV, DBZ and PK packages.

Sink Current Capability: 1 mA to 100 mA TL431 and TL432 devices are available in three grades with an initial tolerance (25°C) of 0.5%, two applications 1% and 2% for B, A and Standard grades, Adjustable voltage and current references. In addition, low output drift with

The secondary-side regulation of the flyback switching power supply temperature ensures a good stability temperature range for the entire system.

Zener replacement

Voltage monitoring TL43xxC devices feature operation from 0°C to 70°C, TL43xxI devices are comparators with an integrated reference and feature operation over a temperature range of -40°C to 85°C, and TL43xxQ devices feature is operated from -40°C to 125°C.

Pin Configuration and Function

Detailed description

Overview

This standard device has proven to be ubiquitous and versatile in a wide range of applications, from power supply to signal path. This is because its key components contain an accurate voltage reference & opamp, which are very basic analog building blocks. The TL43xx is used with its key components as a single voltage reference, error amplifier, voltage clamp or integrated reference comparator.

The TL43xx can operate and regulate over a cathode voltage range of 2.5V to 36V, making this part useful in a wide range of industrial, automotive, telecom, computer and other end equipment. In order for this device to function as a shunt, a regulator or error amplifier greater than 1 mA (max) must be supplied to the cathode pin. In this case, feedback can be applied from the cathode and Ref pins to create a copy of the internal reference voltage.

Various reference voltage options are available for purchase with initial tolerances (25°C) of 0.5%, 1% and 2%. These reference options are denoted by B (0.5%), A (1.0%) and blank (2.0%) after TL431 or TL432. Both the TL431 and TL432 are functional, but have separate pinout options.

TL43xxC devices are characterized for operation over a temperature range of 0°C to 70°C, TL43xxI devices are characterized for operation over a temperature range of -40°C to 85°C, and TL43xxQ devices are characterized for operation over a temperature range of -40°C to 85°C. 85°C operating temperature range to 125°C.

Functional block diagram

Feature description

The TL43xx consists of an internal reference and amplifier based on reference pins and virtual internal pins. The sinking current is generated by the internal Darlington pair, the Darlington pair is used to enable this device to be capable of a maximum current of 100mA.

When operating with sufficient voltage headroom (≥2.5V) and cathode current (IKA), the TL431 forces the reference pin voltage to be 2.5V. However, the reference pin cannot be left floating as it requires IREF ≥ 4µA (see Electrical Characteristics, TL431C, TL432C). This is because the reference pin is driven into an npn that needs a base for current to work properly.

When feedback is applied from the cathode and reference pins, the TL43xx behaves as a Zener diode, regulating a constant voltage depending on the current in the cathode. This is due to the internal amplifier and the reference into the proper operating area. The same current required for the feedback described above must be applied in an open loop, servo or error amplifier setup to give the TL43xx adequate gain in the proper linear region. Unlike many linear regulators, the TL43xx is internally compensated to remain stable between cathode and anode without an output capacitor. However, if an output capacitor is required, a guide to help select the correct capacitor for stability.

Device functional mode

Open loop (comparator)

When the cathode/output voltage or current of the TL43xx is not fed back into any form, the device operates in open loop. In this configuration, the TL43xx has such a high gain when a suitable cathode current (Ika) is applied to the device, typically used for comparators. Integration with a reference makes the TL43xx the preferred level of a single signal when a user is trying to monitor.

closed loop

This device operates in closed loop when the cathode/output voltage or current of the TL43xx is fed back in any form to the reference/input pin. Most applications involving the TL43xx use it in this way to regulate a fixed voltage or current. Feedback enables this device to act like an error amplifier, calculating a fraction of the output voltage and adjusting it to maintain the desired regulation. This is done by returning the output voltage to the reference pin in a way that makes it equal to the internal reference voltage, which can be done through a resistor or direct feedback.

Application and Implementation

Notice

The information in the application section below is not part of the specifications for TI components, and the technical information is not guaranteed to be accurate or complete. TI's customer is responsible for determining part suitability. Customers should validate and test their design implementation to confirm system functionality.

Application Information Since there are many applications and settings for this device, in many cases this data sheet cannot describe in detail. The linked application notes will help the designer make the best choice when using this section.

The application note SLVA482 will provide a deeper understanding of the stability characteristics of this device and help the user make the right choice when choosing a load capacitor. The application note, the SLVA445, helps the designer set the shunt voltage for the best accuracy of the device.

typical application

Integrated reference comparator

Typical Application (continued) Design Requirements For this design example, use the parameters listed in Table 1 as input parameters.

Detailed design procedure

When using the TL431 as a reference comparator, determine the following:

Input voltage range

Reference voltage accuracy

Output Logic Input High and Low Thresholds

Current source resistance

Basic operation

The TL431 will be used as a comparator to compare the VREF pin voltage with an internal virtual reference voltage. The TL43xx will have sufficient open loop gain to provide a fast response when the appropriate cathode current (IK) is supplied. This can be seen in Figure 26, where the RSUP=10kΩ (IKA=500µA) case has a much slower response than RSUP=1kΩ (IKA=5ma). The maximum operating current (IMIN) of the TL43xx is 1 mA, operation below this value may result in low gain, resulting in a slow response.

speeding

A slow or inaccurate response may also occur when the reference pin does not provide sufficient overdrive voltage.

This is the amount of voltage above the internal virtual reference voltage. The internal dummy reference voltage will be in the range of 2.5 V ± (0.5%, 1.0% or 1.5%) depending on the version used. The greater the overdrive voltage this provides, the faster the TL431 responds.

For applications using the TL431 as a comparator, it is best to set the trigger point to be larger than the positive expected error (ie +1.0% of the A version). For fast response, setting the trigger point to the internal VREF should be sufficient.

To minimize the voltage drop or difference from the VIN to the reference pin, it is recommended to provide Iref with an input resistor of less than 10kΩ.

Output Voltage and Logic Input Levels In order to properly use the TL431 as a comparator, the logic output must be readable by the receiving logic device.

The output low voltage of the TL431 in open loop/comparator mode is ~2V, which is typically enough 5V to provide logic. However, the logic provided for 3.3 V and 1.8 V does not work. To accommodate this a resistive voltage divider can be connected to the output to attenuate the output voltage to a voltage that can be recognized by the receiving low voltage logic device.

Since the TL431 is an open collector, the output high voltage of the TL431 is equal to VSUP. If VSUP is greater than the maximum input voltage tolerance of the receiving logic, the output must decay to accommodate the reliability of the output logic.

When using a resistive divider at the output, make sure that the total of the resistive divider is much larger than RSUP so as not to interfere with the TL431's ability to close to VSUP when it turns off.

input resistance

An input resistor is required in this application in order to obtain the desired reference current (IREF) from the device in the correct operating region when Turing is on. The actual voltage at the reference pin is VREF=VIN-IREF*RIN. Since IREF can be as high as 4µA, it is recommended to use a small enough resistor that will mitigate the error that IREF creates from VIN.

Apply Curve

Detailed design procedure

When using the TL431 as a shunt regulator, determine the following:

Input voltage range

temperature range

total accuracy

cathode current

Reference initial accuracy

output capacitor

Program output/cathode voltage

In order to program the cathode voltage as an adjustable voltage, the cathode and anode pins must be connected at the midpoint to the reference pin. This can be seen in Figure 27, using R1 and R2 as a resistor bridge. The cathode voltage can be calculated by calculating the cathode current:

Vo=(1+R1/R2)*VREF-IREF*R1

For this equation to work, the TL43xx must be fully biased so that it has enough open loop gain to reduce any gain error. This can be achieved by meeting the Imin specification shown in Electrical Characteristics TL431C, TL432C.

Detailed design procedure

When using the TL431 as a shunt regulator, determine the following:

Input voltage range

temperature range

total accuracy

cathode current

Reference initial accuracy

output capacitor

Program output/cathode voltage

In order to program the cathode voltage as an adjustable voltage, the cathode and anode pins must be connected at the midpoint to the reference pin. This can be seen in Figure 27, using R1 and R2 as a resistor bridge. The cathode voltage can be calculated by calculating the cathode current:

Vo=(1+R1/R2)*VREF-IREF*R1

For this equation to work, the TL43xx must be fully biased so that it has enough open loop gain to reduce any gain error. This can be achieved by meeting the Imin specification shown in Electrical Characteristics TL431C, TL432C.

total accuracy

When the programmed output is above unity gain (VKA=VREF), the TL43xx is susceptible to other errors that may affect

Overall accuracy exceeds VREF. These errors include:

R1 and R2 Accuracy

VI(dev) - Reference Voltage Over Temperature Variation

VREF/ΔVKA - Variation of reference voltage and cathode voltage

|zKA| - dynamic impedance, causing the cathode voltage to vary with cathode current The worst-case cathode voltage can be determined taking all variables into account. The application description SLVA445 assists the designer in setting the shunt voltage for the best accuracy of the device.

stability

While the TL43xx is stable without a capacitive load, the device receiving the output voltage of the shunt regulator may present a capacitive load within the TL43xx's stability region. Additionally, designers can use capacitive loads to improve transient response or power supply to coupled.

The application note SLVA482 will provide a deeper understanding of the stability characteristics of this device when additional capacitors are used between the cathode and anode and help the user make the right choice when choosing a load capacitor.

Start Time

The TL43xx has a fast response up to ~2V, then slowly charges to the programmed state value. This is due to the compensation capacitors (shown in Figure 24) that the TL43xx must meet its stability criteria. Despite the secondary delay, the TL43xx still has a fast response suitable for many clamping applications.

Apply Curve

System example (continued)

Precision constant flow cell

Power Recommendations

When using the TL43xx as a linear regulator to provide a load, designers typically use the output/cathode pin. When doing this, make sure the capacitor is within the stability criteria shown in To not exceed the maximum cathode current, make sure the supply voltage is current limited. Also, be sure to limit the current to the input reference pin so as not to exceed the Absolute Maximum Ratings.

For applications that shunt large currents, pay attention to the trace lengths of the cathode and anode, and adjust the width to have an appropriate current density.

Layout Guidelines

Bypass capacitors should be placed as close to the part as possible. The current-carrying traces need to have a width appropriate for the currents they carry; for the TL43xx, these currents will be low.

layout example