Microchip MCP4631T-104E/ML 100kΩ Dual Digital Potentiometer Overview and Application Note
Introduction to Digital Potentiometers
Digital potentiometers (digipots) have revolutionized circuit design by replacing traditional mechanical potentiometers with solid-state, digitally-controlled variable resistors. The MCP4631T-104E/ML from Microchip Technology is a prime example of this innovation, offering a compact, reliable, and highly programmable solution for a wide range of analog signal conditioning and calibration applications. This article provides an overview of its key features and discusses practical application circuits.
Device Overview: MCP4631T-104E/ML
The MCP4631 is a dual-channel, 7-bit (128 wiper steps) non-volatile digital potentiometer. The "104" in its part number denotes a nominal end-to-end resistance of 100kΩ. Housed in a miniature 16-pin QFN (4x4mm) ML package, it is designed for space-constrained applications.
Key features include:
Dual Independent Potentiometers: Integrates two 100kΩ potentiometers in a single package, saving board space and cost.
Non-Volatile Wiper Storage: The wiper position (value) is stored in EEPROM memory upon command, meaning it retains its last setting even after a power cycle, which is critical for calibration and initial configuration settings.
Simple Serial Interface: It is controlled via a standard I²C serial interface, allowing communication with a wide array of microcontrollers and processors using only two bus lines.
Low Power Consumption: Features low standby and operating current, making it suitable for battery-powered devices.
Wide Operating Voltage: Supports a supply voltage (VDD) range from 1.8V to 5.5V, enabling operation in both 3.3V and 5V systems.
Application Circuits and Usage
The MCP4631’s versatility allows it to be configured in all the classic ways a mechanical potentiometer is used.
1. Programmable Voltage Divider:
This is the most straightforward application. The device directly functions as a digitally-controlled voltage divider. By connecting Terminal A to a voltage reference (Vref) and Terminal B to ground, the wiper (Terminal W) outputs a variable voltage determined by the programmed wiper position. This is ideal for generating precise reference voltages for ADCs, DACs, or as set-points for other circuits.
2. Variable Gain for Op-Amps:
The MCP4631 excels in controlling the gain of operational amplifier circuits.
Non-Inverting Amplifier: One potentiometer can be used to replace the two fixed resistors in the feedback loop, creating a digitally programmable gain amplifier. The gain can be adjusted on-the-fly via the I²C commands.
Instrumentation Amplifiers: Its dual nature is perfect for simultaneously matching and adjusting the gain-setting resistors in an instrumentation amp configuration, ensuring high common-mode rejection.
3. System Calibration and Trimming:
A primary use case for non-volatile digipots is end-of-line calibration in manufacturing. Parameters like sensor offset, output power, or frequency can be finely tuned by adjusting the digipot. The setting is then saved to EEPROM, making the calibration permanent until a future recalibration is needed, eliminating the need for physical trimming.
Design Considerations:
Wiper Resistance: The wiper itself has a nominal resistance (typically ~75Ω). This can affect performance in very low-resistance applications.
Bandwidth: The digipot has an associated bandwidth; for AC signal applications, ensure its specifications meet the required frequency range.
Voltage Compliance: The analog signals applied to terminals A, B, and W must remain within the supply rails (VSS and VDD).
ICGOODFIND Summary
The Microchip MCP4631T-104E/ML is a highly integrated and efficient dual digital potentiometer. Its non-volatile memory, compact form factor, and simple digital interface make it an superior alternative to mechanical pots. It is an excellent choice for designers seeking to add programmable analog adjustment, automated calibration, and design flexibility to their systems in areas such as industrial control, consumer electronics, automotive, and test and measurement equipment.
Keywords:
Digital Potentiometer, I²C Interface, Non-Volatile Memory, Programmable Gain Amplifier, System Calibration
