Microchip MCP4351-502E/ST Digital Potentiometer: Features, Application Circuit, and Configuration Guide
Digital potentiometers (digipots) have become fundamental components in modern electronic design, replacing mechanical potentiometers for enhanced precision, reliability, and remote control. The Microchip MCP4351-502E/ST is a quad-channel, 8-bit digital potentiometer that offers a versatile and compact solution for a wide range of applications requiring programmable resistance. This article explores its key features, a typical application circuit, and a guide to its configuration.
Key Features of the MCP4351-502E/ST
The MCP4351 is part of Microchip's MCP43xx series of non-volatile digipots. The "502" denotes a nominal end-to-end resistance of 5 kΩ. Its standout features make it an excellent choice for sophisticated designs.
Quad Independent Channels: The device integrates four separate potentiometers in a single 14-pin TSSOP package. This allows for controlling multiple circuit parameters simultaneously, saving board space and reducing component count.
Non-Volatile Wiper Memory: A critical advantage is its ability to retain wiper position in EEPROM memory after power-down. Upon power-up, the device automatically restores the wiper to its last saved position, ensuring consistent operation without the need for microcontroller (MCU) re-initialization.
SPI Interface: It features a simple and fast Serial Peripheral Interface (SPI) for communication with a host MCU. This enables high-speed digital control of the wiper position and device configuration.
Wide Operating Voltage: With an operating voltage range from 1.8V to 5.5V, it is compatible with both 3.3V and 5V logic systems, making it suitable for low-power and battery-operated devices.
Additional Digital I/O: The device provides general-purpose input/output (GPIO) pins that can be controlled via the SPI interface, adding extra utility for system control or status monitoring.
Typical Application Circuit
A common use for the MCP4351 is as a programmable gain controller for an operational amplifier (op-amp). The following circuit illustrates this configuration for one channel.
In this configuration:
1. The MCP4351's `PAx` (Terminal A) and `PBx` (Terminal B) pins are connected across the 5 kΩ fixed resistive element.
2. The `PWx` (Wiper) pin is connected to the inverting input of the op-amp.
3. The op-amp, along with resistors R1 and the digipot, forms a non-inverting amplifier.
4. The gain of the amplifier is given by the formula: Av = 1 + (R_fb / R_top), where `R_top` is the resistance between the wiper (PWx) and Terminal A (PAx), and `R_fb` is the resistance between the wiper (PWx) and Terminal B (PBx).
By sending digital commands over the SPI bus from an MCU, the wiper position is changed, dynamically altering the resistance ratio and thus the gain of the amplifier. This allows for software-controlled, precise gain adjustment without any physical interaction.
Configuration Guide
Configuring the MCP4351 involves sending 16-bit commands over the SPI bus. The command structure is as follows:
Command Bits (C1:C0): These bits select the operation to be performed (e.g., write to wiper, write to memory, read status, configure I/O).
Potentiometer Select Bits (P1:P0): These bits select which of the four potentiometer channels the command addresses.
Data Bits (D9:D0): These 10 bits contain the data for the operation. For an 8-bit wiper write, the 8 Most Significant Bits (MSBs) are used.
A basic sequence to set a wiper position is:
1. Pull the `CS` (Chip Select) pin low to initiate communication.
2. The MCU transmits a 16-bit word. For example, to set the wiper of potentiometer 0 to mid-scale (128 decimal), the command would be `0b0000 1000000000` (Write Wiper command for pot0, data = 128).
3. Pull the `CS` pin high to latch the command and execute it.
To save the current wiper position to non-volatile memory, a separate "Store Wiper to Memory" command must be issued. This command is powerful but should be used judiciously, as the EEPROM has a finite number of write cycles (~1,000,000).
ICGOOODFIND
The Microchip MCP4351-502E/ST stands out as a highly integrated and robust solution for digital resistance control. Its combination of four non-volatile potentiometers, a simple SPI interface, and small form factor provides designers with unparalleled flexibility for automating calibration, tuning, and signal conditioning processes. It is an indispensable component for applications demanding precision, reliability, and remote management.
Keywords:
1. Digital Potentiometer
2. SPI Interface
3. Non-Volatile Memory
4. Programmable Gain
5. Wiper Control
