## AD7691: Overview and Electronic Specifications The **AD7691** is a high-performance, 18-bit, charge redistribution, successive approximation register (SAR) Analog-to-Digital Converter (ADC). It is part of Analog Devices' *PulSAR* family and is designed for low-power, high-precision applications. --- ### 1. Key Technical Specifications The following table summarizes the primary electronic characteristics of the AD7691: | Parameter | Specification | Note | | :--- | :--- | :--- | | **Resolution** | 18 Bits | No missing codes | | **Throughput Rate** | 250 kSPS | Samples per second | | **INL (Integral Nonlinearity)** | ±0.5 LSB (Typical) | High precision linearity | | **Dynamic Range** | 101 dB | Typical at 5V reference | | **Power Consumption** | 1.35 mW | At 250 kSPS, 2.5V supply | | **Supply Voltage (VDD)** | 2.3 V to 5 V | Analog supply range | | **Input Type** | Differential | Improves noise immunity | | **Interface** | SPI / QSPI / MICROWIRE | Serial interface | --- ### 2. Functional Blocks and Features The AD7691 operates on a single power supply and contains several critical internal components: * **SAR Core:** The core architecture uses a capacitive DAC for the successive approximation process. * **Zero-Error Interface:** The serial interface is compatible with 1.8V, 2.5V, 3V, or 5V logic. * **VIO Pin:** A separate digital interface supply allows the chip to communicate with low-voltage microcontrollers without level shifters. * **No Pipeline Delay:** As a SAR ADC, it has no latency, making it ideal for multiplexed applications. --- ### 3. Pin Configuration and Basic Wiring To integrate the AD7691 into a circuit, the following connections are standard: | Pin Name | Function | Description | | :--- | :--- | :--- | | **REF** | Reference Input | Sets the full-scale input range (e.g., 2.5V to 5V). | | **IN+ / IN-** | Analog Inputs | Differential input pair. | | **VDD** | Analog Supply | Power for the internal analog circuitry. | | **VIO** | Digital Supply | Power for the SPI digital interface signals. | | **SCK / SDO / CNV** | Digital I/O | Clock, Data Out, and Convert Start pins. | --- ### 4. Typical Application Circuit When designing with the AD7691, an **RC Filter** is usually placed at the analog inputs to minimize alias interference and limit noise. ```python # Pseudo-code logic for reading the AD7691 via SPI def read_adc(): pulse_high(CNV_PIN) # Trigger conversion wait_conversion_time() # Max 3.2 microseconds data = spi_transfer(0x00) # Clock out 18 bits of data return data ``` ---