TLVH431AIDBZR

The TLVH431AIDBZR is a low-voltage adjustable precision shunt regulator from Texas Instruments, featuring an internal 1.24 V bandgap reference with 1% initial accuracy (A grade) at 25 C. As a three-terminal device, the output voltage can be programmed to any value between VREF (1.24 V) and 18 V by using two external resistive dividers connected to the REF pin. This architecture enables flexible voltage regulation without requiring a fixed-voltage Zener diode for each target output level. The device operates from a minimum cathode current of just 60 uA (typical), significantly lower than the TL431 which requires 1 mA, making it ideal for low-power and battery-operated systems. The wide cathode current range of 100 uA to 70 mA provides substantial design margin for both biasing and load-driving scenarios. With a typical dynamic output impedance of 0.25 Ohm, the TLVH431A delivers tight voltage regulation that outperforms standard Zener diodes by an order of magnitude. The active output circuitry provides a sharp turn-on characteristic, enabling precise threshold behavior in comparator and monitoring applications. When paired with an optocoupler, the TLVH431A serves as the voltage reference and error amplifier in isolated feedback loops for 3 V to 3.3 V switching-mode power supplies, where its low reference voltage enables direct regulation of low-voltage outputs. The industrial-grade (I suffix) version is fully specified from -40 C to +85 C, while Q-suffix versions extend to +125 C with AEC-Q100 Grade 1 qualification for automotive applications.

The TLVH431A operates as a precision shunt regulator through three functional subsystems:

1. Bandgap Reference and Error Amplifier: The core of the device is an internal 1.24 V bandgap voltage reference connected to the non-inverting input of a high-gain comparator. The REF pin serves as the inverting input to this comparator. When the voltage at the REF pin exceeds the internal 1.24 V reference, the error amplifier drives the output Darlington stage to sink more cathode current. Conversely, when the REF pin voltage falls below 1.24 V, the amplifier reduces cathode current. This negative feedback loop forces the REF pin to maintain 1.24 V when the device is in regulation, establishing a stable voltage reference point.

2. Adjustable Output Voltage via External Resistor Divider: When configured with two external resistors R1 (from cathode to REF) and R2 (from REF to anode), the output voltage at the cathode is determined by: VO = VREF x (1 + R1/R2) + Iref x R1. Since Iref is typically only 0.1 uA, the Iref x R1 term is negligible for resistor values below 10 kOhm, yielding VO approximately equal to VREF x (1 + R1/R2). This allows the output voltage to be set from 1.24 V (R1 = 0) up to 18 V (R1/R2 ratio permitting), providing flexibility across a wide range of applications.

3. Shunt Regulation and Dynamic Impedance: The device regulates by shunting excess current from the cathode to the anode. When the output voltage rises above the programmed setpoint, the internal Darlington pair conducts more heavily, sinking additional current and pulling the cathode voltage down. The dynamic output impedance of 0.25 Ohm (typical at f <= 1 kHz) quantifies how effectively the device maintains regulation against load current variations. In the off state (REF pin below 1.24 V), cathode current drops to just 0.02 uA (typical), minimizing power dissipation during standby conditions.

• Isolated SMPS feedback regulation: Paired with an optocoupler in the secondary side of 3 V to 3.3 V flyback converters, the TLVH431A compares a fraction of the output voltage against its 1.24 V reference and drives the optocoupler LED to close the feedback loop, enabling precise output regulation with +/-1% accuracy.
• On-board adjustable voltage reference: Using two external resistors, the device provides a programmable reference from 1.24 V to 18 V for ADC/DAC voltage references, bias networks, or comparator thresholds without needing multiple fixed-voltage Zener diodes.
• Low-leakage Zener replacement: With off-state current of only 0.02 uA and sharp turn-on, the TLVH431A replaces Zener diodes in applications requiring precise voltage clamping with minimal leakage and tight tolerance, such as voltage monitoring and protection circuits.
• Precision current sink: Configured with a sense resistor at the REF pin, the device maintains a constant voltage across the resistor, establishing a precision constant-current sink for LED bias, sensor excitation, or battery charging circuits.
• Power-rail voltage monitor: The sharp threshold at 1.24 V and low reference current make this device suitable for undervoltage and overvoltage detection when combined with a resistive divider and a pull-up resistor on the cathode.