The **TL431K-AE2-R** is a precision programmable shunt voltage reference. It is widely used in power management circuits as a stable voltage reference or an error amplifier in feedback loops. --- ### 1. General Specifications The TL431 is often referred to as an "adjustable Zener diode" because it behaves like a Zener diode with a programmable breakdown voltage. | Parameter | Value / Range | | :--- | :--- | | **Output Voltage ($V_{ref}$)** | 2.495V to 36V (Adjustable) | | **Reference Voltage Accuracy** | ±1% (Standard for K-suffix) | | **Sink Current Capability** | 1.0mA to 100mA | | **Dynamic Impedance** | 0.22 $\Omega$ (Typical) | | **Package Type** | SOT-23-3 (Typical for AE2 suffix) | | **Operating Temperature** | -40°C to +125°C | --- ### 2. Pin Configuration (SOT-23) In the AE2 package variant (SOT-23), the pinout is typically structured as follows: 1. **Reference (REF):** Input to the internal comparator. 2. **Cathode (K):** The "positive" terminal; sinks current from the load. 3. **Anode (A):** The ground or common terminal. --- ### 3. Functional Block Components The internal architecture consists of three main stages: * **Voltage Reference:** A high-stability bandgap reference (typically 2.495V). * **Error Amplifier:** Compares the voltage at the REF pin with the internal reference. * **Output Transistor:** An NPN transistor that sinks current from the Cathode to the Anode based on the error amplifier's output. --- ### 4. Typical Application Circuit To set the output voltage ($V_{out}$), a voltage divider is used between the Cathode and the Reference pin. ```text (Cathode) Vout | [R1] |-------(REF) [R2] | (Anode) GND ``` **Formula for Output Voltage:** $$V_{out} = V_{ref} \times \left(1 + \frac{R1}{R2}\right) + I_{ref} \times R1$$ *(Note: Since $I_{ref}$ is very small, it is often ignored in basic calculations).* --- ### 5. Key Use Cases * **Switch Mode Power Supplies (SMPS):** Used on the secondary side as an error amplifier to provide feedback to an optocoupler. * **Voltage Monitoring:** Acting as a comparator to trigger an alarm or shutdown when a threshold is reached. * **Constant Current Sources:** By placing a precision resistor in the feedback path. ---