MCP4902-ESLASHST datasheet(19/48 Pages) MICROCHIP

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DS22250A-page 19

MCP4902/4912/4922

4.0

GENERAL OVERVIEW

The MCP4902, MCP4912 and MCP4922 are dual

voltage-output 8-bit, 10-bit and 12-bit DAC devices,

respectively. These devices include input amplifiers,

rail-to-rail output amplifiers, reference buffers for

external

voltage

reference,

shutdown

and

reset-management circuitry. The devices use an SPI

serial communication interface and operate with a

single supply voltage from 2.7V to 5.5V.

The DAC input coding of these devices is straight

binary. Equation 4-1 shows the DAC analog output

voltage calculation.

EQUATION 4-1:

ANALOG OUTPUT

VOLTAGE (VOUT)

The ideal output range of each device is:

• MCP4902 (n = 8)

(a) 0 V to 255/256 * VREF when gain setting = 1x.

(b) 0 V to 255/256 * 2 * VREF when gain setting = 2x.

• MCP4912 (n = 10)

(a) 0 V to 1023/1024 * VREF when gain setting = 1x.

(b) 0 V to 1023/1024 * 2 * VREF when gain setting = 2x.

• MCP4922 (n = 12)

(a) 0 V to 4095/4096 * VREF when Gain setting = 1x.

(b) 0 V to 4095/4096 * 2 * VREF when gain setting = 2x.

1 LSb is the ideal voltage difference between two

successive codes. Table 4-1 illustrates the LSb

calculation of each device.

4.1

DC Accuracy

4.1.1

INL ACCURACY

Integral Non-Linearity (INL) error is the maximum

deviation between an actual code transition point and

its corresponding ideal transition point, after offset and

gain errors have been removed. The two end points

(from 0x000 and 0xFFF) method is used for the calcu-

lation. Figure 4-1 shows the details.

A positive INL error represents transition(s) later than

ideal. A negative INL error represents transition(s) ear-

lier than ideal.

FIGURE 4-1:

Example for INL Error.

4.1.2

DNL ACCURACY

A Differential Non-Linearity (DNL) error is the measure

of variations in code widths from the ideal code width.

A DNL error of zero indicates that every code is exactly

1LSb wide.

Note:

See the output swing voltage specification

in Section 1.0 “Electrical Characteris-

tics”.

VOUT

VREF Dn





-------------------------------G

Where:

VREF =EXternal voltage reference

Dn =

DAC input code

Gain Selection

2 for <GA> bit = 0

1 for <GA> bit = 1

DAC Resolution

8 for MCP4902

10 for MCP4912

12 for MCP4922

TABLE 4-1:

LSb OF EACH DEVICE

Device

Gain

Selection

LSb Size

MCP4902

(n = 8)

VREF/256

(2* VREF)/256

MCP4912

(n = 10)

VREF/1024

(2* VREF)/1024

MCP4922

(n = 12)

VREF/4096

(2* VREF)/4096

where VREF is the external voltage reference.

111

110

101

100

011

010

001

000

Digital

Input

Code

Actual

Transfer

Function

INL < 0

Ideal Transfer

Function

INL < 0

DAC Output

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