Analog and Interface Product Solutions Digital Potentiometers Design Guide Supporting digital potentiometer applications, including: mechanical potentiometer replacement, amplifiers with offset and trimming, band pass filtering with offset and gain trimming, programmable filter, Wheatstone bridge trimming and general embedded system design techniques. Design ideas in this guide use the following devices. A complete device list and corresponding data sheets for these products can be found at www.microchip.
Digital Potentiometer Solutions Microchip’s Family of Digital Potentiometers Microchip offers a range of devices that allow the customer to select a device that is a best fit for their application. Some of the selection options include: ■ A wide range of resistor values – RAB resistance (typical) from 2.
Digital Potentiometer Solutions Low Power Applications Normal vs. Shutdown Mode Many applications are power sensitive. This is because they are battery powered or design goals on the power supply. Microchip Technology’s digital potentiometer families are low power, with the maximum IDD as low as 1 μA in some devices. This current is when the serial interface is inactive and a non-volatile memory write cycle is not active.
Digital Potentiometer Solutions Low Voltage Applications 1.8V operational devices are all volatile devices except for the MCP41010, MCP41050, MCP41100, MCP42010, MCP42050 and MCP42100 devices. Some applications require a low operating voltage. Microchip offers most of their volatile memory devices specified down to 1.8V for their digital operation. The analog performance at this low voltage is not specified, but is characterized. For many applications this may be acceptable.
Digital Potentiometer Solutions Small Footprint Applications Small Footprint Devices Some applications have package size limitations and require devices with the smallest footprint possible. Microchip offers several devices in small footprint packages. These packages include 8-pin DFN (3x3 mm and 2x3 mm), 5 and 6-pin SOT-23 and 5 and 6-pin SC70 packages. DFN SOT-23 MSOP 3 mm 4.9 mm Package MSOP DFN (3x3) SOT-23 DFN (2x3) SC70 SC70 DFN 3 mm 2.95 mm 3 mm 3 mm Area (mm2) 2 mm 2 mm 2.
Digital Potentiometer Solutions Non-Volatile Applications This inhibits accidental modification of the wiper setting, as long as the high voltage is not present to the digital potentiometer during normal operation. Many of the non-volatile devices also have some bytes of general purpose EEPROM memory available. This could be used to store system information, such as calibration codes, manufacture date, serial number or user information.
Digital Potentiometer Solutions Serial Interfaces Up/Down Interface Microchip currently offers devices with one of the following three serial interfaces: ■ An Up/Down interface ■ An SPI interface ■ An I2C interface This is an easy to implement interface that requires two pins and can be implemented with minimal software overhead. This interface is also easy for test systems when using the non-volatile devices as replacements for mechanical potentiometers.
Digital Potentiometer Solutions SPI Interface Controller to Single Peripheral with Multiplexed SDI and SDO Pins This is also an easy to implement interface, that requires three or four I/O pins. The additional pins allow data to be read back from the device or to allow device daisy chaining. Daisy chaining allows the SPI interface to update all devices in that chain at the same time. Many microcontrollers offer this interface as a hardware module, further simplifying the code development.
Digital Potentiometer Solutions Volatile (Vol) Non-Volatile (NV) # RS Resistors Rs Ω (typ.) Zero-Scale/ Full-Scale(3) # of Channels WiperLock™ Technology HV Commands Shutdown Mode Configuration Voltage Range # of Pins MCP4131(2) SPI Vol 128 39.1/78.1/390.6/781.3 Y/Y 1 N Y(9) Y(8) Pot 1.8V to 5.5V(6) 8 PDIP, SOIC, MSOP, DFN 5 MCP4132(2) SPI Vol 128 39.1/78.1/390.6/781.3 Y/Y 1 N Y(9) Y(8) Rheo 1.8V to 5.5V(6) 8 PDIP, SOIC, MSOP, DFN 5 MCP4141(2) SPI NV 128 39.1/78.
Digital Potentiometer Solutions I2C™ Interface Controller to Single Peripheral The I2C interface is a two wire interface, where the output drivers are open drain. This protocol supports reads and writes using only the interface’s two wires. The I2C protocol allows multiple devices on the I2C bus, where each device has a unique device address. The I2C protocol requires more host controller firmware overhead than the SPI protocol, but requires less hardware resources (2 pins vs. 3 or 4 pins).
Digital Potentiometer Solutions # RS Resistors Rs Ω (typ.) Zero-Scale/ Full-Scale(3) # of Channels WiperLock™ Technology HV Commands Shutdown Mode Voltage Range # of Pins I2C Vol 127 39.4/78.7/393.7/787.4 Y/Y 1 N N N Rheo 1.8V to 5.5V(6) 6 SC70 5 MCP4018(2) I2C Vol 127 39.4/78.7/393.7/787.4 Y/Y 1 N N N Pot(7) 1.8V to 5.5V(6) 6 SC70 5 MCP4019(2) I2C Vol 127 39.4/78.7/393.7/787.4 Y/Y 1 N N N Rheo(7) 1.8V to 5.5V(6) 5 SC70 5 MCP40D17(2) I2C Vol 127 39.
Digital Potentiometer Solutions Single, Dual and Quad Potentiometer Options Some devices offer multiple resistor networks on the same device. Currently up to 4 resistor networks are available on a single device. These resistor networks are referred to as Pot 0 (Potentiometer 0), Pot 1, Pot 2 and Pot 3. Having multiple potentiometers on the same device offers several advantages, including: ■ Cost per potentiometer ■ PCB layout area per potentiometer ■ Variation between potentiometers Quad Pinout vs.
Digital Potentiometer Solutions Volatile (Vol) Non-Volatile (NV) # RS Resistors Rs Ω (typ.) Zero-Scale/ Full-Scale(3) # of Channels WiperLock™ Technology HV Commands Shutdown Mode Configuration Voltage Range # of Pins MCP4011(1) U/D Vol 63 33.3/79.4/158.7/793.7 Y/Y 1 N Y(9) N Pot 1.8V to 5.5V(6) 8 DFN 2x3 1 MCP4012(1) U/D Vol 63 33.3/79.4/158.7/793.7 Y/Y 1 N Y(9) N Rheo 1.8V to 5.5V(6) 6 SOT 1 5.
Digital Potentiometer Solutions N Y(9) Y(8) Pot 1.8V to 5.5V(6) 14, 16 2 N Y(9) Y(8) Rheo 2 Y Y Y(8) Pot Y Y(8) Rheo 2.7V to 5.5V 10 Y(9) Y(8) Pot 1.8V to 5.5V(6) 14, 16 Y(9) Y(8) Rheo 1.8V to 5.5V(6) 10 Y Y(8) Pot 2.7V to 5.5V 14, 16 SPI Vol 128 39.1/78.1/390.6/781.3 Y/Y MCP4241(2) SPI NV 128 39.1/78.1/390.6/781.3 Y/Y MCP4242(2) SPI NV 128 39.1/78.1/390.6/781.3 Y/Y 2 Y MCP4251(2) SPI Vol 256 19.5/39.1/195.3/390.
Digital Potentiometer Solutions SPI Vol 128 39.1/78.1/390.6/781.3 Y/Y MCP4341(2) SPI NV 128 39.1/78.1/390.6/781.3 Y/Y N Y(9) Y(8) 4 N Y(9) Y(8) Rheo 4 Y Y Y(8) Pot IDD max (μA)(5) 4 Pot 1.8V to 5.5V(6) 20 TSSOP, QFN 5.5V(6) 14 TSSOP 5 20 TSSOP, QFN 5 1.8V to 2.7V to 5.5V Packages # of Pins Y/Y Voltage Range 39.1/78.1/390.6/781.3 Configuration Zero-Scale/ Full-Scale(3) 128 Shutdown Mode Rs Ω (typ.
Digital Potentiometer Solutions Resistance Options and Resolutions Voltage Windowing Microchip offers Digital Potentiometer devices with typical RAB resistances of 2.1 KΩ, 5 KΩ, 10 KΩ, 50 KΩ and 100 KΩ. The devices offer either 6-, 7- or 8-bits of resolution. The step resistance (RS) is the RAB resistances divided by the number of RS resistors in the RAB ladder.
Digital Potentiometer Solutions Application Circuits and Techniques Digital potentiometers are a good fit for applications to trim offset and gain in amplifier circuits. In this following circuit, a resistor ladder is used to create a voltage window where Pot1 is used to trim the desired offset for the inverting amplifier. A second potentiometer (Pot2) is used in a rheostat mode along with resistor R3 to control the gain of the amplifier.
Digital Potentiometer Solutions Logarithmic Steps Logarithmic steps are desirable since the human ear hears in a logarithmic manner. The use of a linear potentiometer can approximate a log potentiometer, but with fewer steps. An 8-bit potentiometer can achieve fourteen 3 dB log steps plus a 100% (0 dB) and a mute setting. The figure below shows a block diagram of one of the MCP44X1 resistor networks being used to attenuate an input signal. In this case, the attenuation will be ground referenced.
Digital Potentiometer Solutions Demo/Evaluation Support Microchip Technology offers several boards that support the demonstration and evaluation of the digital potentiometer devices. These boards fall into two categories: ■ Populated boards to demonstrate/evaluate the specific device(s) ■ Blank printed circuit boards (PCBs) The blank PCBs allow customers to populate the device and supporting circuit to best evaluate the performance and characteristics of the desired device configuration.
Digital Potentiometer Solutions MCP42XX PICtail Plus Daughter Board (MCP42XXDM-PTPLS) This daughter board is used to demonstrate the operation of Microchip’s MCP42XX or MCP41XX digital potentiometers. This board is designed to be used in conjunction with either the PIC24 Explorer 16 Demo Board or the PICkit™ Serial Analyzer. MCP46XX PICtail Plus Daughter Board (MCP46XXDM-PTPLS) This daughter board demonstrates the features and abilities of Microchip’s MCP45XX and MCP46XX Digital Potentiometers.
Digital Potentiometer Solutions AN747: Communicating with Daisy Chained MCP42XXX Digital Potentiometers The MCP41XXX and MCP42XXX family of digital potentiometers allow for daisy chaining of multiple devices on a single SPI bus. It is possible to communicate to multiple devices using one 3-wire data bus (CS, CLK and DATA), by connecting the SO pin on one device to the SI pin of the next device in the chain.
Support Training Microchip is committed to supporting its customers in developing products faster and more efficiently. We maintain a worldwide network of field applications engineers and technical support ready to provide product and system assistance. In addition, the following service areas are available at www.microchip.com: ■ Support link provides a way to get questions answered fast: http://support.microchip.com ■ Sample link offers evaluation samples of any Microchip device: http://sample.
