MCP4822-ESLASHMS datasheet(24/36 Pages) MICROCHIP

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MCP4821/MCP4822

DS21953A-page 24

6.8

Designing A Double-Precision

DAC Using A Dual DAC

Example 6-5 illustrates how to design a single-supply

voltage output capable of up to 24-bit resolution from a

dual 12-bit DAC. This design is simply a voltage divider

with a buffered output.

As an example, if a similar application to the one

developed in Section 6.6.1 “Design a Bipolar DAC

Using Example 6-3” required a resolution of 1 µV

instead of 1 mV, and a range of 0V to 4.1V, then 12-bit

resolution would not be adequate.

Calculate the resolution needed:

4.1V/1 µV = 4.1e06. Since 222 = 4.2e06, 22-bit

resolution is desired. Since DNL = ±0.75 LSb,

this design can be attempted with the MCP482X

family.

Since DACB‘s VOUTB has a resolution of 1 mV,

its output only needs to be “pulled” 1/1000 to

meet the 1 µV target. Dividing VOUTA by 1000

would allow the application to compensate for

DACB‘s DNL error.

If R2 is 100Ω, then R1 needs to be 100 kΩ.

The resulting transfer function is shown in the

equation of Example 6-5.

EXAMPLE 6-5:

Simple, Double-Precision DAC.

MCP482X

VDD

MCP482X

VDD

DACA (Fine Adjust)

DACB (Course Adjust)

SPI™

R1 >> R2

OUTAR2

OUTBR1

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

G = Gain select (1x or 2x)

D = Digital value of DAC (0 – 4096)

0.1 µF

VCC+

VCC–

OUTA

2.048V G

-------

⋅

OUTB

2.048V G

-------

⋅

VOUTA

VOUTB

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