## Overview of the AD7680 The **AD7680** is a high-performance, 16-bit, successive-approximation (SAR) Analog-to-Digital Converter (ADC). It is known for its compact size and low power consumption, making it ideal for battery-powered or space-constrained electronic designs. --- ### Key Technical Specifications | Feature | Specification | | :--- | :--- | | **Resolution** | 16-Bit | | **Throughput Rate** | Up to 100 kSPS (kilo-samples per second) | | **Architecture** | SAR (Successive Approximation Register) | | **Supply Voltage** | 2.5 V to 5.5 V | | **Interface** | SPI/QSPI™/MICROWIRE™/DSP Compatible | | **Package Options** | 6-lead SOT-23 and 8-lead MSOP | | **Power Dissipation** | 3 mW (at 100 kSPS with 3V supply) | --- ### Internal Electronic Architecture The AD7680 consists of several critical functional blocks: 1. **Analog Input Track-and-Hold:** This stage captures the analog input voltage. The AD7680 features a unipolar analog input range from $0V$ to $V_{DD}$. 2. **SAR ADC Core:** The heart of the chip converts the sampled voltage into a 16-bit digital word by comparing the input against a capacitive DAC (Digital-to-Analog Converter) ladder. 3. **Clocking:** The conversion process is controlled by an external serial clock (SCLK), which also shifts out the data. 4. **Reference:** Unlike some ADCs with internal references, the AD7680 uses the **supply voltage ($V_{DD}$)** as the reference. This simplifies the circuit but requires a very stable, low-noise power source for high accuracy. --- ### Pin Configuration (6-Lead SOT-23) | Pin No. | Mnemonic | Description | | :--- | :--- | :--- | | 1 | **$V_{DD}$** | Power Supply and Reference Input. | | 2 | **GND** | Ground Reference. | | 3 | **$V_{IN}$** | Analog Input Channel. | | 4 | **SCLK** | Serial Clock Input (synchronizes data transfer). | | 5 | **SDAT** | Serial Data Output (16-bit conversion result). | | 6 | **$\overline{CS}$** | Chip Select (activates the conversion and frames data). | --- ### Typical Application Circuit To achieve 16-bit performance, specific external components are recommended: * **Decoupling Capacitor:** A 10µF tantalum and a 0.1µF ceramic capacitor should be placed as close as possible to the $V_{DD}$ pin to filter noise. * **Anti-Aliasing Filter:** A simple RC filter (e.g., $100\Omega$ and $1nF$) at the $V_{IN}$ pin helps reduce high-frequency noise. * **Driver Op-Amp:** Since SAR ADCs have switched-capacitor inputs, using a low-noise precision op-amp (like the AD8605) to drive $V_{IN}$ ensures the input settles within the acquisition time. --- ### Digital Timing Diagram (Pseudo-code Logic) The conversion is initiated by the falling edge of $\overline{CS}$. Data is shifted out bit-by-bit on the SCLK pulses. ```c // Pseudocode for reading AD7680 digitalWrite(CS_PIN, LOW); // Start conversion for (int i = 0; i < 16; i++) { bit = shiftIn(SDATA_PIN, SCLK); // Read 16 bits of data } digitalWrite(CS_PIN, HIGH); // End conversion/Reset ```