MCP4802-ESLASHMS datasheet(27/46 Pages) MICROCHIP

27 / 46 page

 2010 Microchip Technology Inc.

DS22249A-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

R23

R2R3

R2 R3

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

V23

VCC+R2



VCC-R3



R2 R3

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

Vtrip

VOUTR23 V23R1

R1 R23

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

R23

V23

VOUT

Thevenin

Equivalent

RSENSE

VOUT

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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