MCP4728 datasheet(47/66 Pages) MICROCHIP

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DS22187C-page 47

MCP4728

6.0

TERMINOLOGY

6.1

Resolution

The resolution is the number of DAC output states that

divide the full scale range. For the 12-bit DAC, the

resolution is 212, meaning the DAC code ranges from 0

to 4095.

6.2

LSB

The least significant bit or the ideal voltage difference

between two successive codes.

EQUATION 6-1:

6.3

Integral Nonlinearity (INL)

Integral nonlinearity (INL) error is the maximum

deviation of an actual transfer function from an ideal

transfer function (straight line). In the MCP4728, INL is

calculated using two end-points (zero and full scale).

INL can be expressed as a percentage of full scale

range (FSR) or in fraction of an LSB. INL is also called

relative accuracy. Equation 6-2 shows how to calculate

the INL error in LSB and Figure 6-1 shows an example

of INL accuracy.

EQUATION 6-2:

INL ERROR

FIGURE 6-1:

INL Accuracy.

6.4

Differential Nonlinearity (DNL)

Differential nonlinearity (DNL) error (see Figure 6-2) is

the measure of step size between codes in actual

transfer function. The ideal step size between codes is

1 LSB. A DNL error of zero would imply that every code

is exactly 1 LSB wide. If the DNL error is less than

1 LSB, the DAC guarantees monotonic output and no

missing codes. The DNL error between any two

adjacent codes is calculated as follows:

EQUATION 6-3:

DNL ERROR

LSB

REF

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

Where

VREF

=VDD

If external reference is

selected

2.048V If internal reference is

selected

The number of digital input bits,

n = 12 for MCP4728.

Full Scale

Zero Scale

–

()

4095

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

Full Scale

Zero Scale

–

()

–

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

INL

OUT

Ideal

–

()

LSB

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

Where:

INL is expressed in LSB

VIdeal

Code*LSB

VOUT

The output voltage measured at

the given input code

010

001

000

Analog

Output

(LSB)

DAC Input Code

011

111

100

101

110

Ideal Transfer Function

Actual Transfer Function

INL = < -1 LSB

INL = 0.5 LSB

INL = - 1 LSB

DNL

ΔV

OUT

LSB

–

LSB

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

Where:

DNL is expressed in LSB.

ΔV

OUT

The measured DAC output

voltage difference between two

adjacent input codes.

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