## Overview of the REF195FS The **REF195FS** is a precision micro-power, low dropout, voltage reference belonging to the REF19x series manufactured by Analog Devices. It is specifically designed to provide a stable **5.0V output** from a wide range of input voltages. The "FS" suffix typically denotes the package type (SOIC-8) and the temperature grade/performance characteristics of the device. --- ### Key Specifications Below are the primary technical parameters for the REF195FS: | Parameter | Value / Description | | :--- | :--- | | **Output Voltage ($V_{out}$)** | 5.0 V | | **Input Voltage Range** | 5.1 V to 15 V | | **Output Current** | Up to 30 mA | | **Quiescent Current** | < 45 $\mu$A (Very Low Power) | | **Dropout Voltage** | 100 mV @ 10 mA load | | **Initial Accuracy** | ±2.0 mV (for F grade) | | **Temperature Coefficient** | 25 ppm/°C | | **Package Type** | 8-lead SOIC (Narrow Body) | --- ### Core Internal Components The REF195FS is more than just a simple regulator; it contains several precision sub-circuits: 1. **Bandgap Reference Core:** The heart of the chip that generates a stable voltage based on the physical properties of silicon transistors. 2. **Error Amplifier:** Monitors the output and compares it to the internal reference to maintain tight regulation. 3. **PMOS Pass Transistor:** Unlike standard regulators that use NPN transistors, the REF195 uses a PMOS design, which allows for the **Low Dropout (LDO)** characteristic. 4. **Shutdown Circuitry:** Includes a "Sleep" mode (via the SLEEP pin) to reduce current consumption to less than 15 $\mu$A when the reference is not needed. --- ### Pin Configuration (SOIC-8) To integrate the REF195FS into a circuit, the following pinout is used: | Pin Number | Name | Function | | :--- | :--- | :--- | | 1 | **TP** | Test Pin (Leave Unconnected) | | 2 | **$V_{in}$** | Supply Voltage Input | | 3 | **SLEEP** | Active Low Shutdown Control | | 4 | **GND** | Ground Reference | | 5 | **TP** | Test Pin (Leave Unconnected) | | 6 | **$V_{out}$** | 5.0V Precision Output | | 7 | **NC** | No Internal Connection | | 8 | **NC** | No Internal Connection | --- ### Typical Application Circuit When wiring the REF195FS, it is recommended to use decoupling capacitors to ensure stability and reduce noise. ```spice Input (5.1V - 15V) ----> [Pin 2: Vin] | [0.1uF Ceramic Cap] | Ground Output (5.0V) <-------- [Pin 6: Vout] | [1.0uF Tantalum Cap] | Ground ``` ### Main Advantages * **High Efficiency:** The extremely low supply current makes it ideal for battery-powered portable instruments. * **Precision:** Low drift over temperature ensures that ADC (Analog-to-Digital Converter) readings remain accurate. * **Load Drive:** Despite being a "reference," it can provide up to 30mA, allowing it to act as a small power supply for precision sensors.