DRV425 Datasheet, PDF (25/37 Pages) Texas Instruments – DRV425 Fluxgate Magnetic-Field Sensor

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DRV425
SBOS729 – OCTOBER 2015
8.2.1.2 Detailed Design Procedure
Use the following procedure to design a solution for a linear-position sensor based on the DRV425:
• Select the proper supply voltage VDD to support the desired magnetic field range (see Table 2 for reference).
• Select the proper reference voltage V_REFIN to support the desired magnetic field range and to match the input
voltage specifications of the desired ADC.
• Use the DRV425 System Parameter Calculator, SLOC331 (RangeCalculator tab) to select the proper shunt
resistor value of R_SHUNT.
• The sensitivity drift performance of a DRV425-based linear position sensor is dominated by the temperature
coefficient of the external shunt resistor. Select a low-drift shunt resistor for best sensor performance.
• Use the DRV425 System Parameter Calculator, SLOC331 (Problems Detected Table in DRV425 System
Parameters tab) to verify the system response.
The amplitude of the magnetic field is a function of distance to and the shape of the magnet, as shown in
Figure 69. If the magnetic field to be measured exceeds 3.6 mT, see the datasheet of the magnet to calculate
the appropriate minimum distance to the DRV425 to avoid saturating the fluxgate sensor.
The high sensitivity of the DRV425 may require shielding of the sensing area to avoid influence of undesired
magnetic field sources (such as the earth magnetic field). Alternatively, an additional DRV425 can be used to
perform difference measurement to cancel the influence of a static magnetic field source, as shown in Figure 68.
Figure 70 shows the differential voltage generated by two DRV425 devices in such a circuit.
Direction of Linear
Movement
DRV425-1
>
REFOUT
REFIN
VOUT
DRV425-2
>
REFOUT
REFIN
VOUT
ADC
Figure 68. Differential Linear-Position Sensing Using Two DRV425 Devices
8.2.1.3 Application Curves
2.6
2.4
2.2
2
1.8
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
0
50 100 150 200 250 300 350 400 450 500
Distance (mm)
D064
1500
1400
1300
1200
1100
1000
900
800
700
600
500
400
300
200
100
0
0
20 40 60 80 100 120 140 160 180 200
Distance (mm)
D065
Figure 69. Analog Output Voltage of the DRV425 vs
Distance to the Magnet
Figure 70. Difference Between Two DRV425 Outputs vs
Distance to the Magnet
Copyright © 2015, Texas Instruments Incorporated
Product Folder Links: DRV425
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