## AD7828LP: High-Speed 8-Channel 8-Bit ADC The **AD7828LP** is a high-speed, multi-channel 8-bit Analog-to-Digital Converter (ADC) manufactured by Analog Devices. It is designed for high-speed data acquisition systems where multiple analog signals need to be digitized rapidly. --- ### 1. Key Technical Specifications The AD7828 series is known for its "Half-Flash" conversion technique, which balances speed and power consumption. | Feature | Specification | | :--- | :--- | | **Resolution** | 8 Bits | | **Input Channels** | 8 Single-Ended Channels | | **Conversion Time** | 2.5 µs (Max) | | **Throughput Rate** | Up to 400 kSPS | | **Supply Voltage** | +5V Single Supply | | **Package Type** | PLCC-28 (indicated by the 'LP' suffix) | | **Power Dissipation** | 75 mW (Typical) | --- ### 2. Internal Architecture and Parts The device consists of several critical internal functional blocks: 1. **Analog Multiplexer:** A 1-of-8 selector that routes one of the eight analog input channels ($V_{IN}0$ to $V_{IN}7$) to the converter. 2. **Half-Flash Converter:** Uses two 4-bit flash stages to achieve 8-bit resolution in a single conversion cycle. 3. **Address Latch:** Stores the 3-bit channel address ($A0, A1, A2$) so the processor doesn't have to hold the address signals during the entire conversion. 4. **Control Logic:** Manages the interface signals like $\overline{RD}$ (Read), $\overline{WR}$ (Write/Convert), and $\overline{CS}$ (Chip Select). 5. **Three-State Output Buffers:** Allows the device to be connected directly to a microprocessor data bus. --- ### 3. Pinout and Interface Signals The 'LP' version comes in a **28-terminal Plastic Leaded Chip Carrier (PLCC)**. Key pins include: | Pin Name | Function | | :--- | :--- | | **DB0 - DB7** | 8-Bit Data Bus Outputs | | **V_IN 0 - 7** | Analog Input Channels | | **A0, A1, A2** | Channel Address Lines | | **$\overline{WR}$ / RDY** | Write signal to start conversion or Ready output | | **$\overline{RD}$** | Read signal to enable output buffers | | **V_REF(+) / V_REF(-)** | Reference voltage inputs (defines the input range) | --- ### 4. Comparison of Operating Modes The AD7828 can operate in two primary modes: * **Mode 0 (Full-Memory Interface):** The conversion is started by a pulse to the $\overline{WR}$ pin. The microprocessor can then read the data after the conversion time has elapsed. * **Mode 1 (Static RAM Interface):** The device behaves like a standard memory location. A $\overline{RD}$ pulse initiates conversion and, once finished, the data is automatically placed on the bus. --- ### 5. Application Areas * **High-speed data acquisition:** Monitoring multiple sensors in real-time. * **Process Control:** Managing multi-variable feedback loops. * **DSP Front-ends:** Providing digital input for signal processors. * **Instrumentation:** Portable or bench-top measuring equipment. ---