MCP4725 datasheet(12/42 Pages) MICROCHIP

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MCP4725

DS22039C-page 12

FIGURE 4-2:

DNL Accuracy.

4.5

Offset Error

Offset error (Figure 4-3) is the deviation from zero volt-

age output when the digital input code is zero. This

error affects all codes by the same amount. In the

MCP4725, the offset error is not trimmed at the factory.

However, it can be calibrated by software in application

circuits.

FIGURE 4-3:

Offset Error.

4.6

Gain Error

Gain error (see Figure 4-4) is the difference between

the actual full-scale output voltage from the ideal output

voltage on the transfer curve. The gain error is

calculated after nullifying the offset error, or full scale

error minus the offset error.

The gain error indicates how well the slope of the actual

transfer function matches the slope of the ideal transfer

function. The gain error is usually expressed as percent

of full-scale range (% of FSR) or in LSB.

In the MCP4725, the gain error is not calibrated at the

factory and most of the gain error is contributed by the

output op amp saturation near the code range beyond

4000. For the applications which need the gain error

specification less than 1% maximum, the user may

consider using the DAC code range between 100 and

4000 instead of using full code range (code 0 to 4095).

The DAC output of the code range between 100 and

4000 is much linear than full-scale range (0 to 4095).

The gain error can be calibrated by software in applica-

tions.

4.7

Full-Scale Error (FSE)

Full-scale error (Figure 4-4) is the sum of offset error

plus gain error. It is the difference between the ideal

and measured DAC output voltage with all bits set to

one (DAC input code = FFFh).

EQUATION 4-4:

FIGURE 4-4:

Gain Error and Full-Scale

Error.

4.8

Gain Error Drift

Gain error drift is the variation in gain error due to a

change in ambient temperature. The gain error drift is

typically expressed in ppm/oC.

010

001

000

Analog

Output

(LSB)

DAC Input Code

011

111

100 101

DNL = 2LSB

DNL = 0.5 LSB

110

Ideal Transfer Function

Actual Transfer Function

Analog

Output

Ideal Transfer Function

Actual Transfer Function

DAC Input Code

Offset

Error

FSE

OUT

Ideal

–

()

LSB

---------------------------------------

Where:

VIdeal

=(VREF) (1 - 2

-n) - V

OFFSET

VREF

The reference voltage.

VREF = VDD in the MCP4725

Analog

Output

Actual Transfer Function

DAC Input Code

Gain Error

Ideal Transfer Function

after Offset Error Removed

Full-Scale

Error

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