A new Digital Potentiometers Design Guide for design ideas supporting digital potentiometer applications, is available from Microchip Technology. It includes: mechanical potentiometer replacement, amplifiers with offset and trimming, band pass filtering with offset and gain trimming, programmable filter, Whetstone bridge trimming and general embedded system design techniques.
Microchip offers a range of devices that allows you to select a product that best fits your application. Some of the selection options include:
* A wide range of resistor values: RAB resistance (typical) from 2,1 kΩ to 100 kΩ.
* Step resolution: 6/8-bit.
* Serial interfaces: up/down/SPI.
* Memory types: volatile/non-volatile.
* Resistor network configurations: potentiometer (resistor divider)/rheostat (variable resistor).
* Single/dual potentiometer options.
* Package options.
* Special features: Shutdown mode/WiperLock technology.
* Low voltage, low power options.
Resistor sizes and resolutions allow the designer to select the step resistance and number of steps. For the device with the resistance (RAB) equal to 2,1 kΩ, there are 64 steps (63 resistors), so the step resistance (RS) equals RAB/63 (or 33,33 Ω). Now at the other end of the spectrum, for the device with the resistance (RAB) equal to 50 kΩ, there are 64 steps (63 resistors), so the step resistance (RS) equals RAB/63 (or 793,65 Ω).
The serial interface options allow you to easily integrate the device into the application. For some applications the simple Up/Down interface will be adequate, while for other applications the SPI interface will better meet your system requirements.
The availability of both volatile and non-volatile devices gives you flexibility in optimising the application. Some applications may use the digital potentiometer as a replacement for a mechanical potentiometer. In this case, a non-volatile device with the serial interface connecting to the test hardware interface allows a low cost device with low cost manufacturing.
Resistor Network configurations allow the package size/cost to be minimised for the desired functionality. If a variable resistor (rheostat) with one terminal tied to ground is desired, then only one resistor terminal (the wiper) needs to be implemented. In the MCP402X family, this configuration is shown in the MCP4024 and allows the functionality to be achieved in the low-cost SOT-23-5 package. The potentiometer pinout with all terminals available requires an 8-pin package.
Dual potentiometer options allow you to have potentiometers/variable resistors that are closely matched in the system, since the two devices are on the same device die. Packaging options help you to address your system requirement trade-offs including device cost, board area and manufacturing sites (surface mount vs. through-hole). Packages include tiny 3x3 SOT-23 and 3x2 DFN packages.
Microchip 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) and blank PCBs. The blank PCBs allow you to populate the device and supporting circuit to best evaluate the performance and characteristics of the desired device configuration.
The guide can be downloaded at ww1.microchip.com/downloads/en/DeviceDoc/22017a.pdf, or contact Arrow Altech Distribution, +27 (0)11 923 9600, Avnet Kopp, +27 (0)11 809 6100, Electrocomp, +27 (0)11 458 9000, Future Electronics, +27 (0)31 262 7743, or Tempe Technologies, +27 (0)11 452 0530.
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