**AD7873ARQ: A Comprehensive Technical Overview and Application Guide**
The **AD7873ARQ** is a highly integrated, 12-bit successive approximation analog-to-digital converter (ADC) specifically designed for touch screen control applications. Housed in a compact 16-pin QSOP package, this device from Analog Devices combines a sophisticated touch screen digitizer with a versatile 4-wire sensing interface and additional auxiliary input channels, making it a cornerstone component for embedded human-machine interfaces (HMIs).
**Core Architecture and Technical Specifications**
At its heart, the AD7873ARQ features a **high-speed 125 kHz successive approximation ADC**. This core is responsible for digitizing the analog signals from the touch screen. The device operates on a single **2.2V to 5.25V supply**, making it compatible with a wide range of system voltages, including 3.3V and 5V logic.
The integrated touch screen controller utilizes a **4-wire analog resistive touch screen** interface. The controller sequentially applies a voltage gradient across one layer of the touch screen and measures the corresponding voltage from the opposing layer using the ADC to determine the X and Y coordinates of the touch point with high accuracy. A dedicated **touch pressure measurement** channel (Z-axis) allows the system to estimate the force of the touch, which can be used to differentiate between a light tap and a hard press.
Beyond the touch screen inputs, the AD7873ARQ offers **two additional auxiliary analog input channels** (IN1, IN2). These can be used to monitor other system variables, such as battery voltage or temperature, from a potentiometer or a thermistor, effectively consolidating multiple measurement functions into a single IC.
Communication with a host microcontroller is achieved via a high-speed **SPI-/QSPI-/MICROWIRE-compatible 3-wire serial interface**. This simple interface minimizes the number of required I/O pins on the host controller. An integrated **2.5V reference** is provided, which can be used for the ADC and is also available externally, simplifying system design and ensuring stable conversion results.
**Key Application Circuits and Design Considerations**
The primary application circuit for the AD7873ARQ involves connecting the four pins (X+, X-, Y+, Y-) directly to the corresponding terminals of a 4-wire resistive touch screen. **Proper debouncing and filtering** on the interrupt output (PENIRQ) are crucial for reliable touch detection. This pin is driven low when a touch is detected, signaling the host controller to initiate a conversion sequence.
To ensure accuracy, attention must be paid to **noise suppression on the analog supply and reference lines**. Bypass capacitors should be placed as close as possible to the device's power pins. The internal reference is typically sufficient for most applications, but for the highest accuracy, especially when using the auxiliary inputs, an external precision reference can be used.
The conversion process is managed by the host controller through the serial interface. The controller sends a command byte to initiate a conversion on a specific channel (X, Y, Z, IN1, IN2, or temperature sensor). The result is then clocked out over the DOUT line. **Averaging multiple consecutive samples** for each coordinate is a common software technique to smooth out noise and improve the precision of the reported touch position.
**Typical Applications and Use Cases**
The AD7873ARQ is ideally suited for a vast array of embedded systems requiring a responsive and reliable user interface.
* **Industrial Controls:** HMIs for PLCs, motor drives, and test and measurement equipment.
* **Portable Instruments:** Handheld multimeters, data loggers, and GPS devices.
* **Point-of-Sale (POS) Terminals:** Payment systems and self-service kiosks.
* **Medical Devices:** Patient monitoring systems and portable diagnostic equipment.
* **Automotive Infotainment Systems:** Central control panels (though automotive-grade parts may be preferred for this environment).
ICGOODFIND: The **AD7873ARQ** stands out as a **highly integrated and versatile solution** for adding touch screen control to embedded designs. Its combination of a **precision 12-bit ADC, dedicated touch screen driver, on-chip reference, and auxiliary inputs** provides exceptional functionality in a minimal footprint. By simplifying the interface between a resistive touch screen and a microcontroller, it accelerates development and ensures robust performance, making it a perennial choice for engineers across numerous industries.
**Keywords:**
1. **Touch Screen Controller**
2. **12-bit ADC**
3. **Resistive Touch Interface**
4. **SPI Interface**
5. **Embedded HMI**
