Data Sheet

ADA4570

APPLICATIONS INFORMATION

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Rev. 0 | 11 of 14

The ADA4570 is designed for magnetoresistive sensing applica-

tions with a differential analog output. The sensor is designed to

operate with an external ADC that is controlled by a separate

processing IC or electronic control unit (ECU) as indicated in

Figure 18.

SUPPLY AND ADC REFERENCE

Connect a decoupling capacitance of 100 nF to the ADA4570 VDD

supply pin to minimize interferences on the power supply from

entering the system. To achieve optimum power supply related

noise performance, connect the VDD supply of the ADA4570 as

the voltage reference of the ADC, as shown in Figure 18. Using

the ADA4570 VDD supply as the reference input voltage to the

external ADC provides a ratiometric configuration where the output

dependency on the supply voltage changes is minimized. This con-

figuration also optimizes the use of the ADC input range because

the output voltages of the VSIN+, VSIN−, VCOS+, and VCOS− pins

track the supply voltage.

CONNECTING THE ADA4570

A typical circuit to connect the ADA4570 to a differential ADC

is shown in Figure 18. The ADA4570 signal driving capability is

sufficient to connect the analog outputs directly to a differential

successive approximation register (SAR) or a Σ-Δ ADC.

Minimize the signal trace lengths to the ADC or the processing

IC. Using proper layout techniques and ground planes around

the analog signal tracks provides shielding on the PCB and im-

proves electromagnetic compatibility (EMC) robustness. For each

outputs (see Figure 18.). The load resistors and capacitors must

match to achieve the best angular accuracy. In addition, take the

desired system sampling frequency into account when adding noise

reducing filters to the front of the ADC.

ANGLE CALCULATION

The angle of the incident magnetic field is calculated from the out-

put of the ADA4570, and the trigonometric function arctangent(2)

(arctan2) is used. To calculate the ADA4570 output angle, use the

following equation:

α = arctan2(VSIN/VCOS)/2

With the sensing range of the AMR sensor, the calculated angle

repeats every 180° rotation of the magnetic field. For a dipole

magnet, the ADA4570 reports an angle with twice the frequency of

the rotation.

The direction of a homogeneous magnetic field for an angle of α =

0°is shown in Figure 19

Figure 19. Direction of Homogeneous Magnetic Field for α = 0°

SIGNAL DEPENDENCE ON AIR GAP

DISTANCE

The ADA4570 measures the direction of the external magnetic field

within the sensor x-y plane.

Within a homogeneous field in the xy direction, where the magnetic

flux density is at least 30 mT, the accuracy and voltage levels of the

angular measurement is independent of the field strength and the

sensor placement in z direction (air gap).

The nominal z distance of the internal x-y plane to the top surface

of the plastic package is shown in Figure 22.

SIGNAL OFFSET AND CALIBRATION

The ADA4570 provides two differential output signals, VSIN and

Matching inaccuracies and other imperfections during the produc-

tion process may result in offsets in the outputs. To minimize

additional offsets, caused by the external filter components, match

the external capacitive and resistive loads to each other by using

the same nominal values for the external components connected to

VSIN+, VSIN−, VCOS+, and VCOS−.

a full magnetic rotation as follows:

The VSIN and VCOS output offset can be removed by subtracting

VSIN and VCOS measurement result.

A single point calibration is usually done at 25°C and removes

the system offset at this temperature. This simple calibration does

not take temperature related offset drifts into account that may be

caused by drifts within the internal or external components. This

calibration may be sufficient for many applications in particular

where no large changes in temperature are expected. To compen-

sate for offset drifts over the full temperature range, dynamic offset

calibrations are required.