TL431CDR - Adjustable Shunt Voltage Reference 2.495V | TI
MPN: TL431CDR ✓ Active| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $0.22 | $0.22 |
| 10 | $0.19 | $1.90 |
| 100 | $0.13 | $13.00 |
| 500 | $0.11 | $55.00 |
| 1,000 | $0.09 | $90.00 |
TL431CDR Overview
A shunt voltage reference is a type of voltage reference IC that regulates voltage by shunting excess current to ground, operating in parallel with the load. Within the power management IC hierarchy, the TL431 functions as a three-terminal programmable reference, an error amplifier, and a Zener-diode replacement, making it one of the most widely used reference topologies in switched-mode power supply (SMPS) feedback loops.
Key features include an adjustable output from Vref (2.495V) up to 36V using two external resistors, a standard-grade initial tolerance of 2.2% (the C grade at 25C), and low output noise. The device operates from -40C to +85C in the C temperature grade and sinks up to 100mA, allowing it to directly drive optocoupler LEDs in isolated flyback converters.
Technically, the TL431 contains an internal 2.495V bandgap reference feeding the inverting input of an output comparator/amplifier stage. When the REF pin voltage exceeds 2.495V, the device conducts cathode current, providing precise closed-loop regulation. According to the TI TL431/TL432 precision programmable reference datasheet, the TL432 variant shares identical electrical specifications with a different pinout only in the DBV, DBZ, and PK packages; B and A grades offer 0.5% and 1% initial accuracy respectively.
Typical applications include isolated SMPS feedback (optocoupler error amplification), adjustable series regulators, overvoltage protection comparators, and analog current-source circuits in industrial power supplies and adapters.
A key design consideration: the device requires a minimum cathode current (approximately 1mA typical) to maintain regulation, so the bias resistor network must guarantee this under all load conditions.
This page synthesizes distributor pricing, drop-in alternatives, comparison tables, and practical design notes not found in the manufacturer datasheet, with pricing as of 2026-10-12.
Drop-in alternatives for TL431CDR — same package, pin-to-pin compatible. Different-package parts requiring PCB rework are excluded.
Quick Comparison Tool — Select alternative parts for side-by-side comparison:
TL431ACDR
✅ Drop-In📋 Reference alternative (not in catalog)
TL431BIDR
✅ Drop-In📋 Reference alternative (not in catalog)
TL431AIDR
✅ Drop-In📋 Reference alternative (not in catalog)
TL431BIDR2G
✅ Drop-In📋 Reference alternative (not in catalog)
KA431
✅ Drop-In📋 Reference alternative (not in catalog)
LM431
✅ Drop-In📋 Reference alternative (not in catalog)
TL431CDR Maximum Ratings & Electrical Characteristics
| Reference Type | Shunt |
| Output Type | Adjustable |
| Reference Voltage | 2.495 V |
| Adjustable Output Range | Vref to 36 V |
| Maximum Cathode Voltage | 36 V |
| Maximum Cathode Current | 100 mA |
| Initial Accuracy (C grade) | 2.2% at 25C |
| Operating Temperature | -40C to +85C |
| Package | SOIC-8 (D) |
| Mounting Type | Surface Mount |
| Pin Compatibility | TL432 (same specs, different pinout in DBV/DBZ/PK packages only) |
| Available Grades | B (0.5%), A (1%), C (2%) initial tolerance at 25C |
| RoHS Status | Compliant |
| Lifecycle Status | Active |
| Manufacturer | Texas Instruments |
TL431CDR Pin Configuration
| Pin 1 | REF — Reference input (2.495V threshold) |
| Pin 2 | ANODE — Anode terminal |
| Pin 3 | ANODE — Anode terminal |
| Pin 4 | ANODE — Anode terminal |
| Pin 5 | ANODE — Anode terminal |
| Pin 6 | CATHODE — Cathode terminal (output/regulation node) |
| Pin 7 | NC — Not connected (per datasheet) |
| Pin 8 | CATHODE — Cathode terminal |
Typical Applications
TL431CDR is suitable for 6 applications: Isolated Flyback SMPS Feedback, Adjustable Series Voltage Regulator, Overvoltage Protection / Crowbar, Precision Current Source and Current Limiter, Voltage Monitor and Supervisory Circuit, Adjustable Reference for ADC and Analog Front Ends.
Isolated Flyback SMPS Feedback
The TL431CDR is the de-facto industry-standard error amplifier in isolated flyback and forward converter feedback circuits. Its 2.495V reference compares the divided output voltage, and the device sinks LED current through an optocoupler (such as PC817) to modulate the PWM controller duty cycle across the isolation barrier. The 36V cathode rating and 100mA sink capability comfortably cover typical 1-10mA optocoupler LED drive requirements, while the 2.2% C-grade reference is accurate enough when combined with 1% divider resistors for consumer adapter output tolerances of about 5%. Frequency compensation (RC network between cathode and REF) is mandatory to stabilize the internal loop formed with the optocoupler CTR and PWM gain.
Recommended
Adjustable Series Voltage Regulator
When paired with an external NPN pass transistor, the TL431CDR forms a precise adjustable series regulator. The TL431 monitors the output via a resistor divider and pulls the pass-transistor base down when the output exceeds the programmed threshold, achieving output voltages from 2.495V up to 36V with line and load regulation far superior to a Zener-transistor regulator. Because the TL431 sinks only up to 100mA, the pass transistor handles the load current while the TL431 supplies the precision. This topology is common in bench supplies, white-good aux rails, and battery charger setpoints, where the 2.2% C-grade accuracy is adequate and the component cost must remain minimal.
Recommended
Overvoltage Protection / Crowbar
The TL431CDR works as an inexpensive, precise overvoltage comparator: a divider from the monitored rail drives the REF pin, and when the rail exceeds the programmed trip point, the TL431 conducts, pulling down the gate of an SCR or driving a latch that disconnects the load. The 2.495V reference with 2.2% tolerance sets an accurate, temperature-stable trip threshold - far better than a raw Zener threshold. Typical uses include protecting 5V logic rails in industrial equipment, clamping automotive 12V inputs, and delaying blow of a fuse via a crowbar SCR. Designers should add a small hysteresis resistor from cathode to REF to prevent chatter near the threshold and verify the 36V absolute maximum against transient events.
Recommended
Precision Current Source and Current Limiter
By sensing the voltage across a shunt resistor with the REF pin, the TL431CDR regulates current: when the shunt drop reaches 2.495V, the device conducts and clamps a MOSFET gate or transistor base, holding current constant. This creates a simple, accurate constant-current sink or charge-current limiter with a threshold set solely by the shunt value - for example, a 2.49-ohm resistor programs a 1A limit. The 2.2% C-grade reference yields a current accuracy of roughly ±3% including resistor tolerance, suitable for LED drivers and battery pre-charge limits. Keep shunt power dissipation in check and place the REF connection directly across the shunt kelvin terminals to avoid layout-induced error.
Recommended
Voltage Monitor and Supervisory Circuit
The TL431CDR serves as a low-cost voltage monitor: a divider scales the supervised rail to the REF pin, and the open-collector-like cathode output pulls low (or signals via pull-up) when the rail crosses the programmed threshold. Chained TL431 stages monitor multiple rails and combine outputs for reset generation or fault flags in microcontroller systems, chargers, and industrial sensors. The 2.495V reference and -40C to +85C C-grade temperature range give stable thresholds across environmental conditions, while the SOIC-8 package shares footprint with higher-accuracy A and B grades, allowing an accuracy upgrade during production without a PCB respin. Add hysteresis for noisy rails to avoid output oscillation.
Recommended
Adjustable Reference for ADC and Analog Front Ends
In cost-sensitive analog front ends, the TL431CDR provides a programmable reference or bias voltage for ADC full-scale setting, comparator thresholds, and sensor excitation. Buffered by an op-amp follower, the TL431-based reference delivers the 2.495V-to-36V range at whatever load the buffer can supply, while the shunt regulator itself handles only microamp-to-milliamp bias currents. The 2.2% initial accuracy of the C grade suits 8-10 bit systems; for 12-bit designs such as the ADC on this site, the B-grade TL431BIDR at 0.5% is the recommended pin-compatible upgrade. Output noise is low for a shunt reference, and adding a small output capacitor with ESR in the stable region preserves loop stability.
Recommended
Recommended Products Summary
Engineering reference data for TL431CDR — comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | TL431ACDR | TL431BIDR | TL431BIDR2G | KA431 | LM431 |
|---|---|---|---|---|---|---|
| Package | SOIC-8 (D) | SOIC-8 (D) - same | SOIC-8 (D) - same | SOIC-8 - same | SOIC-8 (D suffix) - same | SOIC-8 (D suffix) - same |
| Brand | Texas Instruments | Texas Instruments | Texas Instruments | onsemi | onsemi | Texas Instruments |
| Reference Voltage | 2.495 V | 2.495 V | 2.495 V | 2.495 V | 2.495 V | 2.495 V |
| Max Cathode Voltage | 36 V | 36 V | 36 V | 36 V | 36 V | 36 V |
| Max Cathode Current | 100 mA | 100 mA | 100 mA | 100 mA | 100 mA | 100 mA |
Key Differentiators
- Lowest-cost standard grade (vs TL431BIDR)
- Industry-standard SMPS feedback part (vs KA431)
- Same-die accuracy upgrade path (vs TL431ACDR)
Design Notes
Ensure the cathode bias network supplies at least the minimum regulation current (approximately 1mA typical per the TI datasheet family) at all times, especially at low line and with the optocoupler LED drawing current in SMPS designs. A feed resistor sized for 2-5mA at minimum input gives margin. Never rely on the device regulating below Vref (2.495V) - outputs below this require a different reference or an external divider scheme with a lower-threshold part.
Connect the REF pin divider directly at the point of regulation (e.g., at the output capacitor or load terminals) to sense the true output voltage, not at the TL431 pins, to avoid resistive drop errors. Keep the divider resistors in the 1k-100k range: too high and the REF bias current creates error; too low and the divider wastes loop gain. Place the compensation network (typically RC from cathode to REF) close to the IC to minimize noise pickup in the high-impedance REF node.
Do not confuse TL431 and TL432 pinouts: the TL432 swaps pin assignments in DBV, DBZ, and PK packages, so a schematic copied between the two will mis-wire the device. In optocoupler feedback loops, omitting frequency compensation causes output oscillation - the TL431/optocoupler/PWM combination forms a multi-pole loop requiring a dominant-pole RC. Finally, respect the 36V absolute maximum cathode voltage; on off-line converters, snub the primary clamp so leakage-inductance spikes do not reach the feedback pin during transients.
Compliance Information
RoHS compliance indicated on distributor listings (DigiKey/Mouser). REACH, halogen-free, and conflict-minerals status not stated in the provided data.
