+

-

A1

+

-

A2

+5

+5

Pressure

Sensor

0.2mV/Volt/PSI

AV = 100

SCLK

DOUT

/CS

+IN

-IN

ADC161S626

+3.3

6

7

8

9

1

2

3

4,5

VREF

2.02K

100K

100K

DAC121S101

.2uF

.2uF

A1 and A2 = LMP7701

SCLK

DIN

/SYNC

4

5

6

2

3

VA

VOUT

1

3

4

5

2

1

3

4

5

2

1

.1uF

1uF

4

3

2

LM4132-3.3

5

+5

470pF

470pF

180

180

120pF

+5

10

VA

VIO

Copyright © 2016, Texas Instruments Incorporated

21

DAC121S101QML-SP

www.ti.com

SNAS410F – MAY 2008 – REVISED JULY 2016

Product Folder Links: DAC121S101QML-SP

Submit Documentation Feedback

Copyright © 2008–2016, Texas Instruments Incorporated

8.2 Typical Application

Figure 38. Pressure Sensor Gain Adjust

8.2.1 Design Requirements

The DAC121S101QML-SP is a positive supply-only data acquisition system capable of digitizing a pressure

sensor output. In addition to digitizing the pressure sensor output, the system designer can use the DAC121S101

to correct for gain errors in the pressure sensor output by adjusting the bias voltage to the bridge pressure

sensor.

8.2.2 Detailed Design Procedure

As shown in Equation 4, the output of the pressure sensor is relative to the imbalance of the resistive bridge

times the output of the DAC121S101, thus providing the desired gain correction.

Pressure Sensor Output = (DAC_Output × [(R2 / (R1 + R2) – (R4 / (R3 + R4)]

(4)

Likewise for the ADC161S626, Equation 5 shows that the ADC output is function of the Pressure Sensor Output

times relative to the ratio of the ADC input divided by the DAC121S101 output voltage.

ADC161S626 Output = (Pressure Sensor Output × 100 / (2 × VREF)) × 2

16

(5)