MCP4902-ESLASHST datasheet(31/48 Pages) MICROCHIP

31 / 48 page

 2010 Microchip Technology Inc.

DS22250A-page 31

MCP4902/4912/4922

6.6

Selectable Gain and Offset Bipolar

Voltage Output Using a Dual DAC

In some applications, precision digital control of the

output range is desirable. Example 6-4 illustrates how

to use the MCP4902/4912/4922 to achieve this in a

bipolar or single-supply application.

This circuit is typically used in Multiplier mode and is

ideal for linearizing a sensor whose slope and offset

varies. Refer to Section 6.9 “Using Multiplier Mode”

for more information on Multiplier mode.

The equation to design a bipolar “window” DAC would

be utilized if R3, R4 and R5 are populated.

EXAMPLE 6-4:

BIPOLAR VOLTAGE SOURCE WITH SELECTABLE GAIN AND OFFSET

VREFA

DACB

VDD

DACA

VDD

DACA (Gain Adjust)

DACB (Offset Adjust)

SPI

VCC+

Thevenin

Bipolar “Window” DAC using R4 and R5

0.1uF

VCC–

VCC+

VCC–

VOUTB

VREFBGB



-------

VOUTA

VOUTB

VOUTA

VREFAGA



-------

VIN+

VOUTBR4 VCC-R3

R3 R4

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

VIN+ 1

------



 V

OUTA

------





–

Equivalent

V45

VCC+R4 VCC-R5

R4 R5

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

R45

R4R5

R4 R5

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

VIN+

VOUTBR45 V45R3

R3 R45

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

VIN+ 1

------



 V

OUTA

------





–

Offset Adjust Gain Adjust

VREFB

GX = Gain selection (1x or 2x)

DA, DB = Digital value of DAC (0-255) for MCP4902

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

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

N = DAC Bit Resolution

Dual Output DAC:

MCP4902

MCP4912

MCP4922

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