Microchip MCP4011T-202E/SN 7-Bit Digital Potentiometer: Features and Application Circuit Design
The Microchip MCP4011T-202E/SN is a compact, 7-bit (128 wiper steps) volatile digital potentiometer, providing a digitally controlled variable resistor solution. This device serves as a modern, solid-state replacement for traditional mechanical potentiometers and trimmers, enabling precise adjustments through a simple digital interface. It is particularly valuable in space-constrained applications and systems requiring automated calibration, volume control, or programmable voltage settings.
Key Features of the MCP4011T-202E/SN
This digital pot, offered in a space-saving 8-pin SOIC (SN) package, is designed for ease of integration and robust performance. Its standout features include:
7-Bit Resolution: Offers 128 resistor tap points for fine-grained adjustment of resistance.
Nominal Resistance: A 2 kΩ end-to-end terminal resistance (RAB), suitable for many low-power signal and control applications.
Simple Digital Interface: Utilizes a 2-wire I²C-compatible serial interface for communication, simplifying control from microcontrollers (MCUs) or other digital logic.
Volatile Wiper Memory: The wiper position resets to a mid-scale (64/128) upon power-up. This is sufficient for applications where the setting does not need to be stored after power removal.
Low Power Consumption: Operates with a wide supply voltage range (2.7V to 5.5V) and features very low standby and active current, making it ideal for battery-powered devices.
High Reliability: As a solid-state device, it eliminates the wear-and-tear, noise, and physical size issues associated with mechanical pots.
Application Circuit Design
A typical application circuit for the MCP4011T-202E/SN involves using it as a programmable voltage divider or a variable resistor. Below is a fundamental circuit design and explanation.
1. Programmable Voltage Reference Circuit
One of the most common uses is generating an adjustable voltage reference from a fixed source. This is crucial for setting thresholds in comparators, bias points for amplifiers, or reference levels for ADCs.
Circuit Description:
The VDD pin (Pin 1) and the A terminal (Pin 8) are connected to the positive supply rail (e.g., +3.3V or +5V).
The B terminal (Pin 7) is connected to ground.
The W (wiper) terminal (Pin 6) is the output, providing a variable voltage between VDD and GND.
The SDA (Pin 4) and SCL (Pin 3) lines are connected to the corresponding pins of a host microcontroller, pulled up to VDD with resistors (typically 4.7 kΩ).
The VSS pin (Pin 2) is tied to ground.
The A0 pin (Pin 5) is the device address select. Since this is a single device on the bus, it can be connected directly to GND.
Operation:
The microcontroller sends commands over the I²C bus to set the wiper's position. The output voltage at the W pin is calculated as:
VW = VDD (Wiper_Value / 127)
For example, with a 5V supply and a wiper value of 64, VW would be approximately 2.52V.
2. Variable Gain Control for an Op-Amp
The MCP4011T can be configured as a variable resistor in the feedback loop of an op-amp to create a non-inverting amplifier with digitally programmable gain.
Circuit Description:
The B and W terminals are shorted together, effectively creating a two-terminal variable resistor (RWB).
This variable resistance (RWB) is placed in series with another resistor (R1) in the feedback path between the output and the inverting input of the op-amp.
A fixed resistor (R2) is connected from the inverting input to ground.
Operation:
The gain of this non-inverting amplifier is set by:
Gain = 1 + ( (R1 + RWB) / R2 )
By sending digital commands to change the value of RWB, the overall gain of the amplifier can be precisely and remotely controlled without any manual intervention.
Design Considerations:
Bandwidth: The internal capacitance of the digital pot can limit bandwidth in high-frequency signal applications.
Wiper Resistance: The ~100Ω wiper resistance (RW) adds a small error in series with the set value, which is often negligible in low-current applications but should be considered for precision designs.
Voltage Compliance: The analog signals applied to terminals A, B, and W must remain within the supply rails (VSS to VDD).
ICGOODFIND: The Microchip MCP4011T-202E/SN stands out as an exceptionally easy-to-use and cost-effective solution for adding digital adjustability to analog circuits. Its I²C interface and small form factor make it a perfect choice for modern designs dominated by MCUs, enabling automation and programmability in audio equipment, sensor calibration modules, power supplies, and test and measurement gear. Its primary strength lies in simplifying complex mechanical adjustment processes into a sleek, software-controlled command.
Keywords:
1. Digital Potentiometer
2. I²C Interface
3. Programmable Voltage Divider
4. Variable Gain Amplifier
5. Automated Calibration
