MCP4821 datasheet(27/50 Pages) MICROCHIP

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DS20002249B-page 27

MCP4802/4812/4822

6.5.1.2

Building a “Window” DAC

When calibrating a set point or threshold of a sensor,

typically only a small portion of the DAC output range is

utilized. If the LSb size is adequate enough to meet the

application’s accuracy needs, the unused range is

sacrificed without consequences. If greater accuracy is

needed, then the output range will need to be reduced

to increase the resolution around the desired threshold.

If the threshold is not near VREF, 2VREF or VSS, then

creating a “window” around the threshold has several

advantages. One simple method to create this

“window” is to use a voltage divider network with a pull-

up and pull-down resistor. Example 6-2 shows this

concept.

EXAMPLE 6-2:

SINGLE-SUPPLY “WINDOW” DAC

DAC

VDD

SPI

3-wire

VTRIP

0.1 µF

Comparator

VCC-

VCC+

VCC-

VOUT

2R3

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

CC+R2



CC-R3



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

trip

OUTR23

23R1

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

R23

V23

VOUT

Thevenin

Equivalent

RSENSE

OUT

2.048 G

------



(a) Single Output DAC:

MCP4801

MCP4811

MCP4821

(b) Dual Output DAC:

MCP4802

MCP4812

MCP4822

Gain selection (1x or 2x)

Dn = Digital value of DAC (0-255) for MCP4801/MCP4802

Digital value of DAC (0-1023) for MCP4811/MCP4812

Digital value of DAC (0-4095) for MCP4821/MCP4822

DAC bit resolution

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