Digital Potentiometer Glossary

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A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

Analog Crosstalk - CTA

This is the ratio of the amplitude of the signal at the wiper of one RDAC to a sine wave applied to terminal A of another RDAC. It is measured in dBs.

Bandwidth¹ - BW

Frequency at which the output falls to 2/2 of the maximum value.

Crosstalk - CT

This is the area of the glitch transferred to the output of one RDAC due to the full-scale change in the output of another RDAC. The area of the glitch is expressed in nV-secs.

Differential Nonlinearity - DNL

Differential Nonlinearity is the difference between the measured change and the ideal 1 LSB change between any two adjacent codes. A DNL of ±1 LSB maximum ensures monotonicity. A non-monotonic device is defined as a device that has one or more levels of analog output that may actually be less than the values corresponding to codes of smaller weight.

Digital Potentiometer -- DigiPOT, VR, Variable Resistor

The Digital Potentiometer is an integrated circuit that performs the same resistance adjustment as a mechanical trimmer or Rheostat. In addition, it can be configured to perform the three-terminal mechanical potentiometer voltage divider function. Digital Potentiometers are known by several abbreviated names: E²POT, DACPOT, VR, variable resistor, RDAC, Rheostat, etc.

Full Scale Error - V_WFSE

In the voltage divider mode, this is the error in the RDAC output voltage with all 1’s loaded to the RDAC. Ideally the output voltage, with all 1’s loaded to the RDAC registers, should be V_A. The error is expressed in LSBs.

This is a measure of the maximum deviation from a straight line passing through the endpoints of the RDAC transfer function. It is expressed in LSBs. In other words, for a nonlinear device, the differences between heights of adjacent values are not equal.

Nominal Resistor Tolerance - R_AB

Possible deviation of R_AB from its ideal value measured as a percentage.

Power Supply Sensitivity - PSS

Power supply sensitivity is the sensitivity of a converter to changes in the power-supply voltages. This is normally expressed in terms of the percent of full-scale change in the output for a 1% dc change in the power supply.

Resistor Noise Voltage¹ - e_{N_WB}

This is defined as random noise generated by internal resistors. It is characterized as a spectral density (voltage per root Hertz).

Resistor Temperature Coefficient - R_AB / T

This is a measure of the dependency of R_AB's value on temperature. It is measured in ppm/°C which is found from (R/T)*(10^6/R_AB).

Resolution - N

A measure of the adjustability of the resistor value. To convert bits(N) to number of steps, simply do the following...steps = 2^N.

SCL Clock Frequency - fSCL

Maximum allowable clock frequency.

Settling Time¹ - t_s

The time required, following a data change, for the output to reach and remain within ±0.5 LSB of the final value.

Voltage Divider Temp. Coefficient - Vw/ T

In the voltage divider mode, the output voltage is dependant on the ratio of the internal resistors RWA and RWB and not their absolute values. Because of this, the temperature coefficient is reduced when compared to the Rheostat mode. It is measured in ppm/°C.

Voltage Range - VA,B,W

Maximum allowable voltage across resistor terminals. Note: the resistor terminals have no limitations on polarity with respect to each other.

Wiper Resistance - RW

The wiper resistance is the resistance of the transmission gate, which is the physical switch that implements the data conversion.

Zero Scale Error - V^WZSE

In the voltage divider mode, this is the error in the RDAC output voltage with all 0's loaded to the RDAC. Ideally the output voltage with all 0's loaded to the RDAC registers should be 0. The error is expressed in LSBs.

NOTES

¹Bandwidth, settling time, and noise are all functions of the terminal resistance value chosen. The lowest R value results in the highest bandwidth, fastest settling time, and lowest noise. The highest R value results in the minimum overall power consumption.

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