MCP4921 datasheet(29/50 Pages) MICROCHIP

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 2010 Microchip Technology Inc.

DS22248A-page 29

MCP4901/4911/4921

6.4.1.2

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 or VSS, then creating

“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 and

Example 6-4 illustrate this concept.

EXAMPLE 6-2:

SINGLE-SUPPLY “WINDOW” DAC.

VREF

VDD

SPI

Vtrip

0.1 µF

Comparator

VCC-

VCC+

VCC-

VOUT

2R3

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

CC+ R2



CC-R3



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

tr ip

OUTR23

23R1

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

R23

V23

VOUT

Thevenin

Equivalent

Rsense

G = Gain selection (1x or 2x)

Dn = Digital value of DAC (0-255) for MCP4901/MCP4902

OUT

REF

------



= Digital value of DAC (0-1023) for MCP4911/MCP4912

= Digital value of DAC (0-4095) for MCP4921/MCP4922

N = DAC Bit Resolution

DAC

MCP4901

MCP4911

MCP4921

(a) Single Output DAC:

(b) Dual Output DAC:

MCP4902

MCP4912

MCP4922

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