Digital potentiometers
23 May 2001
Analogue, Mixed Signal, LSI
Expanding its suite of standalone analog components for digital designers, Microchip Technology has introduced the MCP4XXXX family of six single and dual-channel digital potentiometers with an SPIT interface. Both single and dual-channel versions are available with resistor values of 10, 50 and 100 kOhm; the wiper position for each potentiometer is changed using a standard SPIT serial interface. A software shutdown command in the dual-channel devices provides the means for reducing current consumption while not in use by allowing the user to open circuit each resistor individually. The dual channel devices also feature a shut-down pin that performs the same function.
The MCP4XXXX features high accuracy at 8 bit resolution (256 wiper steps); single supply operation of 2,7-5,5 V; low static current of 1 µA maximum; and an industrial temperature range of -40 to +85°C. The devices offer INL and DNL of ±1 LSB maximum.
In a typical application, the system MCU will send an initialisation value at power on; alternatively the potentiometers will reset to mid-scale on power up. The digital potentiometers can be used in both the voltage divider and rheostat modes. The dual-channel devices can be connected in series to simplify communication and control. The digital solution provides the ability to control system parameters under CPU command if desired. Systems requiring complex calibration or tuning during and after manufacturing can now be automatically calibrated, eliminating the need for manual calibration. Permanent settings can be saved in microcontroller EEPROM during power off.
Applications for the MCP4XXXX family include audio equipment (volume and tone controls), servo-motor control, battery charging and control, communications (line impedance matching), power supplies, instrumentation (gain, offset adjust), LCD contrast control and programmable filters. The devices can be used in many existing Microchip customer designs using analog-to-digital converters (ADCs), op-amps and microcontrollers.
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