MCP4822-ESLASHMS datasheet(20/36 Pages) MICROCHIP

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MCP4821/MCP4822

DS21953A-page 20

6.5

Single-Supply Operation

The MCP482X devices are Rail-to-Rail (R-R) input and

output DACs designed to operate with a VDD range of

2.7V to 5.5V. Its output amplifier is robust enough to

drive common, small-signal loads directly, thus eliminat-

ing the cost and size of an external buffer for most

applications.

6.5.1

DC SET POINT OR CALIBRATION

A common application for a DAC with the MCP482X

family’s performance is a digitally-controlled set point

and/or calibration of variable parameters, such as sen-

sor offset or slope. 12-bit resolution provides 4096 out-

put steps. If G = 1 is selected, then the internal 2.048

VREF would produce 500 µV of resolution. If G = 2 is

selected, the internal 2.048 VREF would produce 1 mV

of resolution.

6.5.1.1

Decreasing The Output Step Size

If the application is calibrating the threshold of a diode,

transistor or resistor tied to AVSS, a threshold range of

0.8V may be desired to provide 200 µV resolution. Two

common methods to achieve a 0.8V range is to either

reduce VREF to 0.82V (would require MCP492X device

and external voltage reference) or use a voltage divider

on the DAC’s output. Typically, when using a low-

voltage VREF, the noise floor causes SNR error that is

intolerable. The voltage divider method provides some

advantages when VREF needs to be very low or when

the desired output voltage is not available. Using two

resistors to scale the output range down to the precise

desired level is a simple, low-cost method to achieve

very small step sizes. Example 6-1 illustrates this

concept. Note that the bypass capacitor on the output

of the voltage divider plays a critical function in

attenuating the output noise of the DAC and the

induced noise from the environment.

The

MCP482X

family’s

low

±0.75

(max.)

DNL

performance is critical to meeting calibration accuracy

in production.

EXAMPLE 6-1:

Set Point or Threshold Calibration.

MCP482X

VDD

SPI™

VTRIP

0.1 uF

Comparator

G = Gain select (1x or 2x)

D = Digital value of DAC (0 – 4096)

OUT

2.048 G

---------

⋅

VCC+

VCC–

VOUT

trip

OUT

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

⎝⎠

⎜⎟

⎛⎞

VDD

RSENSE

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