The **REF30xx** and **REF31xx** (often collectively referred to as the **REF3** family) are a series of high-precision, low-power, low-dropout, CMOS voltage references developed primarily by Texas Instruments. These components are essential in electronic design to provide a stable, constant voltage "baseline" for Analog-to-Digital Converters (ADCs) and Digital-to-Analog Converters (DACs). --- ### 1. Key Technical Specifications The REF3 family is favored for its small footprint (typically SOT23-3 packages) and high efficiency. | Feature | Specification (Typical) | | :--- | :--- | | **Output Voltages** | 1.25V, 2.048V, 2.5V, 3.0V, 3.3V, 4.096V | | **Input Voltage Range** | $V_{OUT} + 50mV$ to 5.5V | | **Quiescent Current** | ~100 µA to 120 µA | | **Drift (Temperature)** | 20 ppm/°C to 50 ppm/°C | | **Output Current** | Up to 10 mA (source/sink) | | **Initial Accuracy** | ±0.2% | --- ### 2. Internal Block Diagram Overview The internal circuitry of a REF3 device generally consists of three main stages: 1. **Bandgap Reference:** The core "engine" that generates a stable voltage by balancing the negative temperature coefficient of a PN junction against the positive temperature coefficient of a thermal voltage ($V_T$). 2. **Error Amplifier:** High-gain operational amplifier that ensures the output remains stable despite changes in load or input voltage. 3. **Output Buffer:** Provides the necessary drive current (low impedance) to power the reference pins of high-speed converters without dropping voltage. --- ### 3. Connection and Application Because the REF3 is a **Series Reference**, it is connected in series with the load, similar to a linear regulator. #### Typical Wiring Diagram ```text (Input Supply) ---- [ IN ]-------[ REF3xx ]-------[ OUT ] ---- (To ADC Vref+) | | [ GND ] [ C_out ] (0.1uF - 1uF) | | (Ground) -------------------- (Ground) ``` #### Common Use Cases * **Battery-Powered Equipment:** Due to low quiescent current ($<125\mu A$). * **Data Acquisition Systems:** Providing the reference for 12-bit and 14-bit ADCs. * **Precision Industrial Sensors:** Stability across a temperature range of -40°C to +125°C. --- ### 4. Comparison: Series vs. Shunt | Feature | Series (REF3xx) | Shunt (e.g., LM4040) | | :--- | :--- | :--- | | **Efficiency** | Higher (only draws current needed by load) | Lower (always draws max current through resistor) | | **Complexity** | Simple 3-pin setup | Requires external resistor calculation | | **Best For** | Varying input voltages | Very noisy supplies |