Texas Instruments TLV431BCPK

Overview

TLV431BCPK from Texas Instruments is a low-voltage adjustable precision shunt regulator with 0.5% initial reference voltage tolerance at 25°C, 1.24V nominal VREF, and operation down to 1.24V cathode-anode voltage. It delivers 0.25Ω typical dynamic impedance, 80µA typical minimum cathode current, and supports output voltage adjustment from 1.24V to 6V using two external resistors. It serves as a Zener diode replacement in isolated flyback secondary-side regulation circuits.

For engineers reviewing the TLV431BCPK datasheet, TLV431BCPK pinout, TLV431BCPK application, or TLV431BCPK equivalent, key selection considerations include its SOT-89-3 package footprint (4.5mm × 4.095mm), ±4mV reference drift over 0°C to 70°C, ultra-low I_REF (0.1–0.5µA), and compatibility with optocoupler-based feedback in 3.3V SMPS designs.

Technical Context

The TLV431BCPK operates as a 3-terminal adjustable shunt reference with an internal bandgap-derived 1.24V reference and high-gain NPN-based error amplifier. Its functional modes include open-loop comparator operation (with integrated reference) and closed-loop shunt regulation-both enabled by cathode current ≥55µA and proper REF-to-CATHODE feedback configuration.

Unlike the TL431, it achieves regulation at lower headroom (≥1.24V VKA) and lower minimum cathode current (≤100µA), making it suitable for low-voltage systems. The device is internally compensated and stable without an output capacitor, though capacitive load stability depends on VKA and CL per Figure 5-19–5-21.

Key Specifications

Pinout & Package

SOT-89-3 (PK) package with exposed thermal pad; 3-pin surface-mount outline measuring 4.5mm × 4.095mm. Pin 1 = CATHODE, Pin 2 = ANODE, Pin 3 = REFERENCE.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar shunt-regulator applications.

Compared with TLV431BCPK, TLV431ACPK trades 0.5% accuracy for lower unit cost while maintaining identical thermal and dynamic performance, whereas TLVH431IPK extends voltage and current capability at the expense of pinout compatibility and increased quiescent current.

Availability

TLV431BCPK is available at Aetrix Electronics and suitable for isolated flyback SMPS design, precision voltage monitoring, and low-voltage Zener replacement applications requiring stable component supply across commercial and industrial temperature ranges.

Supply support for TLV431BCPK includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Texas Instruments is a global semiconductor company delivering analog and embedded processing solutions, with leadership in precision analog, power management, and signal chain technologies.

The TLV431 family was designed specifically for low-voltage, high-accuracy shunt regulation in space-constrained power systems-including isolated DC/DC converters, battery monitors, and programmable references-replacing legacy TL431-based designs with improved efficiency and smaller footprint.

FAQ

What is the maximum cathode current rating for TLV431BCPK?

The absolute maximum continuous cathode current for TLV431BCPK is 20 mA, per Section 5.1 Absolute Maximum Ratings. However, the recommended operating condition limits IK to 15 mA for reliable long-term operation at TA ≤70°C. At higher temperatures or with elevated power dissipation, derating is required-e.g., ≤10 mA at 85°C ambient-to maintain junction temperature below 150°C.

Can TLV431BCPK replace TL431 in existing designs?

TLV431BCPK can replace TL431 only if the circuit operates with ≥1.24V cathode-anode voltage and supports the lower 0.5% reference tolerance. It cannot substitute in 2.5V-reference-only TL431 circuits without resistor-divider recalibration. Also, TLV431BCPK's lower I_K(min) (55µA vs. 1mA) may cause instability in legacy TL431 feedback networks designed for higher bias current.

What is the thermal resistance (RθJA) of TLV431BCPK in SOT-89 package?

The junction-to-ambient thermal resistance (RθJA) for TLV431BCPK in the PK (SOT-89-3) package is 52°C/W, as specified in Table 5.4 Thermal Information. This value assumes standard JEDEC 2-layer board conditions (2 oz copper, 1 in² copper pour under thermal pad). With proper PCB copper area, TLV431BCPK sustains 15 mA cathode current at 70°C ambient without exceeding 125°C junction temperature.

Does TLV431BCPK require an output capacitor for stability?

No, TLV431BCPK is internally compensated and stable without an output capacitor between CATHODE and ANODE. However, when driving capacitive loads (e.g., optocoupler CTR variation or long PCB traces), stability must be verified using Figures 5-19 to 5-21 in the datasheet. For CL > 100 pF at VKA = 5V, phase margin drops below 45°, requiring series resistance or reduced CL.

How does the REF pin function in TLV431BCPK open-loop comparator mode?

In open-loop comparator mode, the REF pin serves as the input threshold node: when voltage at REF exceeds 1.24V (±0.5%), the internal amplifier saturates and pulls CATHODE low. The REF pin draws only 0.1–0.5 µA, enabling direct connection to high-impedance sources like RC networks or sensor outputs-no external buffer is needed unless source impedance exceeds 100 kΩ.