## Overview of TL432-AB3-R The **TL432-AB3-R** is a three-terminal adjustable shunt regulator with specified thermal stability. It is often described as a "programmable zener diode" because its output voltage can be set to any value between $V_{ref}$ (approx 1.25V) and 18V using two external resistors. The "AB3" suffix typically denotes the package type (**SOT-89**), and the "R" denotes the packing (Tape & Reel). --- ### 1. Key Technical Specifications | Parameter | Value / Description | | :--- | :--- | | **Reference Voltage ($V_{ref}$)** | 1.24V to 1.26V (1.25V Nominal) | | **Cathode Voltage ($V_{ka}$)** | $V_{ref}$ to 18V | | **Cathode Current ($I_k$)** | 80 $\mu$A to 100 mA | | **Reference Input Current** | 0.15 $\mu$A (Typical) | | **Dynamic Impedance** | 0.2 $\Omega$ (Typical) | | **Operating Temperature** | -40°C to +125°C | | **Package Type** | SOT-89 | --- ### 2. Pin Configuration (SOT-89) The TL432 has a different pinout compared to the standard TL431 in some packages. For the SOT-89 package (AB3): 1. **REF**: The reference input. 2. **CATHODE**: The positive terminal (equivalent to a Zener cathode). 3. **ANODE**: The negative terminal (ground). --- ### 3. Functional Description The device operates by comparing the voltage at the **REF** pin to an internal 1.25V bandgap reference. * If the voltage at REF increases above 1.25V, the internal transistor conducts more current from Cathode to Anode. * If the voltage at REF drops below 1.25V, the device reduces conduction. #### Output Voltage Formula To set the output voltage ($V_{out}$), a resistor divider ($R_1$ and $R_2$) is used: $$V_{out} = V_{ref} \times (1 + \frac{R_1}{R_2}) + I_{ref} \times R_1$$ *(Note: Since $I_{ref}$ is very small, it is often ignored for general calculations).* --- ### 4. Applications * **Linear Regulators:** Used as the reference element for adjustable power supplies. * **Switching Power Supplies:** Frequently used in the feedback loop (with an optocoupler) to provide isolated voltage regulation. * **Voltage Monitoring:** Acts as a precise comparator for over-voltage or under-voltage detection. * **Constant Current Source:** Can be configured to maintain a steady current across a load. --- ### 5. Comparison: TL431 vs. TL432 The primary difference between the TL431 and TL432 series is the **Internal Reference Voltage**: * **TL431:** Reference voltage is **2.5V**. * **TL432:** Reference voltage is **1.25V**. This makes the TL432 ideal for low-voltage applications (e.g., 1.8V or 3.3V rails) where a 2.5V reference is too high to provide effective regulation.