MCP4921 datasheet(16/40 Pages) MICROCHIP

16 / 40 page

MCP4921/4922

DS21897A-page 16

 2004 Microchip Technology Inc.

4.0

GENERAL OVERVIEW

The MCP492X devices are voltage output string DACs.

These devices include input amplifiers, rail-to-rail out-

put amplifiers, reference buffers, shutdown and reset-

management circuitry. Serial communication conforms

to the SPI protocol. The MCP492X operates from 2.7V

to 5.5V supplies.

The coding of these devices is straight binary and the

ideal output voltage is given by Equation 4-1, where G

is the selected gain (1x or 2x), DN represents the digital

input value and n represents the number of bits of

resolution (n = 12).

EQUATION 4-1:

LSB SIZE

1 LSB is the ideal voltage difference between two

successive codes. Table 4-1 illustrates how to calculate

LSB.

4.0.1

INL ACCURACY

INL error for these devices is the maximum deviation

between an actual code transition point and its corre-

sponding ideal transition point once offset and gain

errors have been removed. These endpoints are from

0x000 to 0xFFF. Refer to Figure 4-1.

Positive INL means transition(s) later than ideal.

Negative INL means transition(s) earlier than ideal.

FIGURE 4-1:

INL Accuracy.

4.0.2

DNL ACCURACY

DNL error is the measure of variations in code widths

from the ideal code width. A DNL error of zero would

imply that every code is exactly 1 LSB wide.

FIGURE 4-2:

DNL Accuracy.

4.0.3

OFFSET ERROR

Offset error is the deviation from zero voltage output

when the digital input code is zero.

4.0.4

GAIN ERROR

Gain error is the deviation from the ideal output,

VREF– 1 LSB, excluding the effects of offset error.

TABLE 4-1:

LSB SIZES

Device

VREF, GAIN

LSB SIZE

MCP492X

External VREF, 1x

VREF/4096

MCP492X

External VREF, 2x

2 VREF/4096

OUT

REFGDN

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

111

110

101

100

011

010

001

000

Digital

Input

Code

Actual

transfer

function

INL < 0

Ideal transfer

function

INL < 0

DAC Output

111

110

101

100

011

010

001

000

Digital

Input

Code

Actual

transfer

function

Ideal transfer

function

Narrow code < 1 LSB

DAC Output

Wide code, > 1 LSB

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