MCP4821 datasheet(21/36 Pages) MICROCHIP

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DS21953A-page 21

MCP4821/MCP4822

6.5.1.2

Building a “Window” DAC

When calibrating a set point or threshold of a sensor,

rarely does the sensor utilize the entire output range of

the DAC. If the LSb size is adequate to meet the appli-

cation’s accuracy needs, the resolution 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 AVSS, 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-

and

pull-down

resistor.

Example 6-2

and

Example 6-4 illustrates this concept.

The

MCP482X

family’s

low

±0.75

(max.)

DNL

performance is critical to meet calibration accuracy in

production.

EXAMPLE 6-2:

Single-Supply “Window” DAC.

MCP482X

VDD

SPI™

VTRIP

0.1 µF

Comparator

VCC-

G = Gain select (1x or 2x)

D = Digital value of DAC (0 – 4096)

VCC+

VCC-

VOUT

OUT

2.048 G

-------

⋅

2R3

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

CC+R2

()

CC-R3

()

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

trip

OUTR23

23R1

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

R23

V23

VOUT

Thevenin

Equivalent

RSENSE

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