TL431AIPK - 2.495V Adjustable Shunt Reference, SOT-89 | TI
MPN: TL431AIPK ✓ Active| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $0.29 | $0.29 |
| 10 | $0.23 | $2.30 |
| 100 | $0.15 | $15.00 |
| 500 | $0.12 | $60.00 |
| 1,000 | $0.1 | $100.00 |
TL431AIPK Overview
A shunt voltage reference is a type of voltage reference IC that regulates by shunting excess current to ground, holding a fixed voltage across its terminals. Within the power-management hierarchy (voltage reference -> shunt regulator -> power management IC -> semiconductor), shunt references are valued for their simplicity: the output voltage can be set to any value between Vref (approximately 2.5 V) and 36 V using only two external resistors, according to TI product documentation.
Key features of the TL431AIPK include the A-grade ±1% reference tolerance at 25C, low output temperature-drift behavior, a wide adjustable output range from 2.495 V to 36 V, and operation from 1 mA minimum cathode current up to 100 mA. Because the internal bandgap reference and output stage are fully specified over the industrial temperature range, the device provides stable regulation across commercial and industrial environments.
Technically, the TL431 behaves like an op-amp with a 2.495V internal reference on its inverting input: when the REF pin rises above Vref, the cathode conducts and pulls the cathode voltage down, making it a building block for error amplifiers in isolated flyback power supplies, comparators with precise thresholds, and series pass elements.
Typical applications include optocoupler feedback error amplification in AC-DC and DC-DC switching supplies, adjustable voltage monitors and threshold comparators, and local regulation of analog supply rails.
Design consideration: keep cathode current above the 1 mA minimum for regulation and respect the 36V maximum cathode-to-anode voltage; the divider resistors should be sized to limit Iref-induced error.
This page synthesizes distributor pricing, drop-in alternatives across TI grade variants, and practical design notes not found in the manufacturer datasheet.
Drop-in alternatives for TL431AIPK — same package, pin-to-pin compatible. Different-package parts requiring PCB rework are excluded.
Variants in this series
Same-series models that are drop-in compatible with TL431AIPK (same form factor and footprint) — differing in Package.
Quick Comparison Tool — Select alternative parts for side-by-side comparison:
TL431ACPK
✅ Drop-In📋 Reference alternative (not in catalog)
TL431IPK
✅ Drop-In📋 Reference alternative (not in catalog)
TL431CPK
✅ Drop-In📋 Reference alternative (not in catalog)
TL431AIPKG3
✅ Drop-In📋 Reference alternative (not in catalog)
TL431AIPKQ1
✅ Drop-In ⚠️ Specs Unverified📋 Reference alternative (not in catalog)
TL431AIPK Maximum Ratings & Electrical Characteristics
| Reference Type | Shunt |
| Reference Voltage | 2.495 V (Vref) |
| Initial Tolerance | ±1% (A grade, at 25C) |
| Output Type | Adjustable, 2.495 V to 36 V |
| Maximum Cathode Current | 100 mA |
| Minimum Cathode Current for Regulation | 1 mA |
| Maximum Cathode Voltage | 36 V |
| Operating Temperature Range | -40C to +85C (I grade) |
| Package | SOT-89-3 (PK, 3-pin + tab) |
| Mounting Type | Surface Mount |
| MSL Level | MSL 2 - 260C - 1 year |
| RoHS Status | Compliant |
| Packaging | Tape & Reel (T/R) |
| Configuration | 3-terminal (Cathode, Anode, REF) |
TL431AIPK Pin Configuration
| Pin 1 | REF — Reference input - compare node against internal 2.495V reference |
| Pin 2 | ANODE — Anode terminal - lowest potential, connect to ground rail |
| Pin 3 | CATHODE — Cathode terminal - regulates current sink; also connected to the metal tab |
Typical Applications
TL431AIPK is suitable for 6 applications: SMPS Optocoupler Feedback Error Amplifier, Adjustable Shunt Voltage Regulation, Precision Voltage Comparator / Threshold Detector, Battery Charger Voltage Regulation Loop, Programmable Reference for ADC/DAC Systems, Overvoltage Protection and Crowbar Circuits.
SMPS Optocoupler Feedback Error Amplifier
The TL431AIPK is the de facto standard secondary-side error amplifier in isolated flyback and forward AC-DC converters. Its 2.495V reference compares the sensed output voltage through a resistor divider, and the cathode sinks current from an optocoupler LED (typically limited to 1-10 mA by a series resistor), modulating the primary-side PWM controller. The ±1% A-grade tolerance directly translates into output-voltage accuracy of the finished supply, and the wide 36V cathode rating covers 5V, 12V, 19V, and 24V output rails. A compensation network (typically an RC from REF to cathode) stabilizes the loop; the 1 mA minimum cathode current sets the minimum bias requirement and must be guaranteed at no-load for regulation.
Recommended
Adjustable Shunt Voltage Regulation
Connected with a single series resistor from an unregulated rail, the TL431AIPK functions as a complete low-power shunt regulator delivering any rail between 2.495V and 36V at up to 100 mA. Because it regulates by shunting current rather than dropping it in series, it is inherently short-circuit-safe on the load side (bounded by the series resistor) and requires no output capacitor for stability in basic configurations. Typical uses include bias rails for analog front ends, local regulation of 5V logic from noisy supplies, and clamp circuits protecting sensitive nodes. Power dissipation in the SOT-89 package (VIN - VOUT) x ICATHODE must be respected; the tab provides thermal relief on the PCB.
Recommended
Precision Voltage Comparator / Threshold Detector
The TL431AIPK's REF input behaves like the inverting input of an op-amp with a built-in 2.495V reference, so driving REF above Vref pulls the open-collector-like cathode low - creating a precision comparator with an inherent threshold. With a divider at REF, thresholds from 2.5V up to 36V are set with ±1% accuracy, far better than bare comparator ICs with external references. Applications include undervoltage/overvoltage monitoring, battery low-voltage cutoff, power-good indication, and crowbar triggers for SCR protection. The open cathode output can directly sink LED indicators or drive transistor bases, though designers must account for the device's finite gain and slew characteristics versus dedicated comparators.
Recommended
Battery Charger Voltage Regulation Loop
In Li-ion and lead-acid charger designs, the TL431AIPK regulates the float/termination voltage by comparing a divider at the battery node against its 2.495V reference and controlling a pass element or optocoupler feedback path. The ±1% initial tolerance matters because Li-ion float accuracy requirements (typically ±1% at the cell) consume the entire error budget - designers often combine the TL431 tolerance with precision divider resistors to stay within spec. The 36V cathode rating supports multi-cell stacks, and the industrial -40C to +85C range covers automotive and outdoor charging environments. Compensation around the TL431 prevents oscillation when driving MOSFET pass transistors or converter feedback loops.
Recommended
Programmable Reference for ADC/DAC Systems
While not a ultralow-noise series reference, the TL431AIPK serves as an economical programmable reference source for moderately accurate data-converter systems. Adjusted via two resistors, it generates reference rails (for example 3.0V or 4.096V approximately, derived from its adjustable output) for ratiometric ADC measurements and DAC output scaling in industrial monitoring nodes. Its ±1% tolerance suits 8- to 10-bit ratiometric accuracy levels; for 12-bit+ systems, series references with tighter drift are preferred. Shunt operation provides good ripple rejection when fed through a series resistor from a noisy switching rail, and the low cost allows per-channel referencing in multi-channel acquisition designs built around SAR ADCs.
Recommended
Overvoltage Protection and Crowbar Circuits
The TL431AIPK makes a precise OV trigger: a divider monitors the protected rail, and when the node exceeds 2.495V x (1 + R1/R2), the cathode sinks base/gate current into an SCR or MOSFET crowbar, or pulls down an enable pin to latch off the supply. Compared to zener-based triggers, the TL431 threshold is adjustable and ±1% accurate, avoiding the wide tolerance and knee softness of zener diodes. Its 100 mA sink capability directly drives small SCRs; larger crowbars use a transistor buffer. The industrial temperature range ensures thresholds do not drift out of protection windows across -40C to +85C operation, important in telecom -48V rail monitoring and industrial 24V bus protection circuits.
Recommended
Recommended Products Summary
Engineering reference data for TL431AIPK — comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | TL431ACPK | TL431IPK | TL431CPK | TL431AIPKG3 | TL431AIPKQ1 |
|---|---|---|---|---|---|---|
| Package | SOT-89-3 (PK) | SOT-89-3 (PK) - same | SOT-89-3 (PK) - same | SOT-89-3 (PK) - same | SOT-89-3 (PK) - same | SOT-89-3 (PK) - same |
| Brand | Texas Instruments | Texas Instruments | Texas Instruments | Texas Instruments | Texas Instruments | Texas Instruments |
| Reference Tolerance | ±1% (A grade) | ±1% (A grade) | ±2.4% (standard) | ±2.4% (standard) | ±1% (A grade) | ±1% (A grade) |
| Reference Voltage | 2.495 V | 2.495 V | 2.495 V | 2.495 V | 2.495 V | 2.495 V |
| Adjustable Output Range | 2.495 V to 36 V | 2.495 V to 36 V | 2.495 V to 36 V | 2.495 V to 36 V | 2.495 V to 36 V | 2.495 V to 36 V |
| Max Cathode Current | 100 mA | 100 mA | 100 mA | 100 mA | 100 mA | 100 mA |
| Operating Temperature | -40C to +85C (I grade) | 0C to +70C (C grade) | -40C to +85C (I grade) | 0C to +70C (C grade) | -40C to +85C (I grade) | -40C to +125C (Q1 automotive) |
| Automotive Grade (AEC-Q100) | No | No | No | No | No | Yes (Q1) |
Key Differentiators
- ±1% reference tolerance at industrial temperature range (vs TL431IPK)
- Wide 36V cathode rating in a compact SOT-89 package (vs TL431ACPK)
- Lower cost with relaxed accuracy available (vs TL431AIPK (as baseline))
Design Notes
Always guarantee the minimum 1 mA cathode current across all load and line conditions - below this the TL431AIPK leaves regulation and output voltage accuracy collapses. Size the series resistor so ICATHODE at maximum output load still exceeds 1 mA, while at minimum load the resistor limits current below 100 mA and keeps dissipation within SOT-89 ratings. Estimated: for a 12V input, 5V output shunt setup, (12V-5V)/1k = 7 mA continuous, dissipating about 49 mW in the device - well within limits.
When the TL431AIPK operates inside an optocoupler feedback loop, the loop gain includes the TL431, the optocoupler CTR (which degrades with LED current and age), and the PWM controller. Add a compensation network - typically an RC (for example 100nF + series resistor) from REF to cathode - to roll off gain and guarantee phase margin. According to TI datasheet application sections, instability without compensation is the most common field failure mode for TL431-based flyback supplies.
The SOT-89 (PK) package tab is electrically the cathode; provide a copper pour under the tab to improve thermal dissipation when the device sinks tens of milliamps across a large VIN-VOUT delta. Estimated: at 36V cathode, 20 mA, dissipation is 0.72W, which is significant for SOT-89 - check junction temperature against the package theta-JA before finalizing. Keep the REF divider close to the pin and use 1% or better resistors so the divider does not dominate the ±1% reference error budget.
Do not confuse TL431 and TL432 in the PK package: they have different pinouts (REF/ANODE swapped in some packages per TI documentation), so a TL432 will not work on a TL431 footprint. Also verify the grade suffix: TL431AIPK is ±1% industrial grade; accidentally BOM-substituting TL431IPK or TL431CPK halves reference accuracy and reduces temperature range - both fail silently in finished systems rather than at test.
Compliance Information
RoHS compliant and MSL 2 - 260C - 1 year per distributor compliance data (PartGenie). REACH, halogen-free, and conflict-minerals status not stated in retrieved data.
