DRV425 Datasheet, PDF (17/37 Pages) Texas Instruments – DRV425 Fluxgate Magnetic-Field Sensor

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7 Detailed Description
DRV425
SBOS729 – OCTOBER 2015
7.1 Overview
Magnetic sensors are used in a broad range of applications (such as position, indirect ac and dc current, or
torque measurement). Hall-effect sensors are most common in magnetic field sensing, but their offset, noise,
gain variation, and nonlinearity limit the achievable resolution and accuracy of the system. Fluxgate sensors offer
significantly higher sensitivity, lower drift, lower noise, and high linearity and enable up to 1000-times better
accuracy of the measurement.
As shown in the Functional Block Diagram section, the DRV425 consists of a magnetic fluxgate sensor with the
necessary sensor conditioning and compensation coil to internally close the control loop. The fluxgate sensor is
repeatedly driven in and out of saturation and supports hysteresis-free operation with excellent accuracy. The
internal compensation coil assures stable gain and high linearity.
The magnetic field (B) is detected by the internal fluxgate sensor in the DRV425. The device integrates the
sensor output to assure high-loop gain. The integrator output connects to the built-in differential driver that drives
an opposing compensation current through the internal compensation coil. The compensation coil generates an
opposite magnetic field that brings the original magnetic field at the sensor back to zero.
The compensation current is proportional to the external magnetic field and its value is 12.2 mA/mT. This
compensation current generates a voltage drop across an external shunt resistor, R_SHUNT. An integrated
difference amplifier with a fixed gain of 4 V/V measures this voltage and generates an output voltage that is
referenced to REFIN and is proportional to the magnetic field. The value of the output voltage at the VOUT pin
(V_VOUT) is calculated using Equation 1:
V_VOUT [V] = B × G × R_SHUNT × G_AMP = B [mT] × 12.2 mA/mT × R_SHUNT [Ω] × 4 [V/V]
(1)
7.2 Functional Block Diagram
RSHUNT
COMP1
COMP2
DRV2
Fluxgate Sensor Front-End
Compensation
Coil
Fluxgate
Integrator
Sensor
Differential
Driver
DRV1 AINP
AINN
Shunt
Sense
Amplifier
VOUT
REFIN
Device Control
DRV425
Voltage Reference
REFOUT
OR ERROR BSEL
RSEL0 RSEL1
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