MCP4822-ESLASHMS datasheet(25/36 Pages) MICROCHIP

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DS21953A-page 25

MCP4821/MCP4822

6.9

Building A Programmable Current

Source

Example 6-6 illustrates a variation on a voltage follower

design where a sense resistor is used to convert the

DAC’s voltage output into a digitally-selectable current

source.

Adding the resistor network from Example 6-2 would

be advantageous in this application. The smaller

RSENSE is, the less power dissipated across it.

However, this also reduces the resolution that the

current can be controlled with. The voltage divider, or

“window”, DAC configuration would allow the range to

be reduced, thus increasing resolution around the

range of interest. When working with very small sensor

voltages, plan on eliminating the amplifier's offset error

by storing the DAC's setting under known sensor

conditions.

EXAMPLE 6-6:

Digitally-Controlled Current

Source.

MCP482X

Rsense

Load

VDD

SPI™

VCC+

VCC–

VOUT

G = Gain select (1x or 2x)

D = Digital value of DAC (0 – 4096)

OUT

se nse

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

β 1

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

OUT

2.048V G

-------

⋅

----

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