MCP4716 datasheet(49/70 Pages) MICROCHIP

49 / 70 page

 2012 Microchip Technology Inc.

DS25154A-page 49

MCP47A1

8.2

Selectable Gain and Offset Bipolar

Voltage Output

In some applications, control of the output range is

desirable. Figure 8-4 shows a circuit using a DAC

device to achieve a bipolar or single-supply application.

This circuit is typically used for linearizing a sensor

whose slope and offset varies. Depending on the out-

put range desired, resistor R4 or resistor R5 may not be

required. Equation 8-4 shows the calculation of the

Gain, while Equation 8-5 shows the calculation of the

VO voltage.

This circuit can be simplified if the window range is

limited (by removing either the R4 or R5 resistor).

Figure 8-5 shows a circuit for the case where the R5

resistor is removed. Resistors R1 and R2 control the

gain, while resistors R3 and R4 shift the DAC's output

to a selected offset. Equation 8-6 shows the calculation

of the VO voltage.

FIGURE 8-4:

Bipolar Voltage Source with

Selectable Gain and Offset Circuit.

FIGURE 8-5:

Simplified Bipolar Voltage

Source with Selectable Gain and Offset Circuit.

EQUATION 8-4:

GAIN CALCULATION

EQUATION 8-5:

BIPOLAR “WINDOW” DAC

CALCULATIONS

EQUATION 8-6:

SIMPLIFIED BIPOLAR

“WINDOW” DAC

CALCULATIONS

Note:

R4 can be tied to VDD, instead of VSS, if a

higher offset is desired.

VCC+

VCC–

I2C™

2-wire

VREF

MCP47A1

VDD

VOUT

VIN

VOA+

VCC+

VCC–

Note: Capacitor C1 is recommended (0.1uF typical)

VCC+

VCC–

I2C™

2-wire

VREF

MCP47A1

VDD

VOUT

VIN

VOA+

Note: Capacitor C1 is recommended (0.1uF typical)

Gain =

If desired Gain = 0.5, and R1 is selected as 20 k

then R2 would need to be 10 k .

Offset Adjust

Gain Adjust

VOA+ =

(VOUT • R45) + (V45 • R3)

R3 + R45

VO = VOA+ • ( 1 +

) - VIN • (

)

VOUT = N * VS

(1)

Note 1: V

OUT calculation does not take into

account RFS and RZS resistors of the DAC’s

resistor ladder (see

Section 7.1 for additional

information).

V45 =

(VCC+ • R4) + (VCC- • R5)

R4 + R5

R45 =

R4 • R5

R4 + R5

VS =

VREF

192

VOA+ = VOUT • (

)

R3 + R4

VO = VOA+ • ( 1 +

) - VIN • (

)

VOUT = N * VS

Note 1: V

OUT calculation does not take into

account RFS and RZS resistors of the DAC’s

resistor ladder (see

Section 7.1 for additional

information).

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