**AD7828KNZ: A Comprehensive Guide to the 8-Channel 500 kSPS SAR ADC**

In the realm of data acquisition systems, the ability to accurately and efficiently convert real-world analog signals into digital values is paramount. The **AD7828KNZ from Analog Devices** stands out as a robust solution, integrating an **8-channel multiplexer** with a high-speed, low-power **Successive Approximation Register (SAR) Analog-to-Digital Converter (ADC)**. This device is engineered for applications demanding simultaneous multi-channel sampling or rapid sequential sampling across multiple inputs, making it a versatile choice for industrial control, instrumentation, and medical systems.

**Architecture and Key Features**

At the heart of the AD7828KNZ is a precision **SAR ADC core** capable of conversion rates up to **500 kilosamples per second (kSPS)**. The SAR architecture is renowned for its simplicity and speed, providing a deterministic conversion time without the latency typically associated with delta-sigma (ΔΣ) ADCs. This makes it ideal for control loops and other time-critical applications.

The device features a **built-in 8-channel single-ended multiplexer**, allowing a single ADC to sequentially digitize up to eight different analog voltage sources. The on-chip track-and-hold amplifier acquires the input signal in under 500 ns, ensuring accurate capture of fast-changing signals. The AD7828KNZ operates from a single **2.7 V to 5.25 V supply**, making it compatible with both 3 V and 5 V systems. Its power consumption is remarkably low, typically drawing just 8 mW at 500 kSPS with a 5 V supply, and it features a flexible power-down mode that reduces current consumption to 1 µA, enhancing efficiency in battery-powered or portable devices.

The digital interface is parallel, with an 8-bit tri-state output bus, facilitating easy connection to microprocessors, microcontrollers, and digital signal processors (DSPs). The **8-bit resolution** provides 256 discrete output codes, with a typical integral nonlinearity (INL) error of ±0.5 LSB, ensuring good accuracy across the entire analog input range.

**Operation and Application**

Operation is straightforward. The three address lines (A0, A1, A2) select the desired input channel. A conversion is initiated by pulling the **CONVST (Conversion Start)** pin low. The BUSY pin then goes high, indicating that a conversion is in progress. Once complete, the result is available on the parallel data output bus and can be read by pulling the **RD (Read)** pin low.

The combination of high speed and multiple channels makes the AD7828KNZ exceptionally useful in systems monitoring several sensors. For instance, in a **programmable logic controller (PLC)**, it can read temperatures, pressures, and voltages from various points. In medical devices, it can be used to monitor multiple patient vitals from different sensors.

**Design Considerations**

While powerful, designers must consider several factors to maximize performance. **Proper bypassing** with 10 µF and 0.1 µF capacitors close to the power supply pins is crucial to minimize noise. The analog input should be driven by a low-impedance source to avoid acquisition errors. For dynamic signals, an external op-amp driver might be necessary to ensure the signal settles within the track-and-hold's acquisition window.

Due to its parallel interface, the AD7828KNZ requires more microcontroller I/O pins than a serial ADC. This is a trade-off for the simplicity and speed of a parallel data transfer. For space-constrained designs, this pin count must be considered in the system layout.

**ICGOOODFIND**

The AD7828KNZ is a highly integrated, high-performance data acquisition solution. Its **8-channel input multiplexer, 500 kSPS conversion rate, and low-power operation** make it an excellent choice for multi-channel systems where speed, efficiency, and integration are critical. Its straightforward parallel interface and robust performance simplify design-in for a wide range of industrial and instrumentation applications.

**Keywords:**

SAR ADC

500 kSPS

8-Channel Multiplexer

Low Power

Parallel Interface