ADA4571

Data Sheet

Rev. 0 | Page 16 of 21

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APPLICATIONS INFORMATION

The integrated AMR sensor is designed for applications with a

separate processing IC or electronic control unit (ECU) containing

an ADC with references connected to the supply voltage. With

AMR sensor output, the system is inherently ratiometric and the

signal dependency on supply voltage changes are minimized.

ANGLE CALCULATION

To calculate angle from the output of the AMR device, use the

trigonometric function arctangent2. The arctangent2 function

is a standard arctangent function with additional quadrant

information to extend the output from the magnetic angle range

of −90° to +90° to the magnetic angle range of −180° to +180°.

Because of the sensing range of AMR technology, this

calculated magnetic angle repeats over each pole of the magnet.

For a simple dipole magnet, the following equation reports

absolute angle over 180° mechanical:

2

)

arctan(

COS

SIN

V

V





CONNECTION TO ECU

Because of the limited driving capability of the ADA4571

output, minimize the length of printed circuit board (PCB)

traces between the ADA4571 and other IC. Shielding of the

signal lines is recommended. Match the load capacitors and

resistors for best angular accuracy. Add bandwidth limitation

filters related to the sampling frequency of the system in front

of the ADC inputs to reduce noise bandwidth.

In Figure 29, the load resistors on VCOS and VSIN are

representing the input load of the filter and the ADC. The

processor may be used for arctan and offset calculations, offset

storage, and additional calibration.

VTEMP Output Pin

A proportional to absolute temperature circuit provides a

voltage output at the VTEMP pin for temperature monitoring

or temperature calibration purposes. The output voltage is

ratiometric to the supply voltage enabling the interface with an

ADC that uses the supply voltage to generate the reference

voltage. This pin must be left open when not in use.

To achieve maximum accuracy from the VTEMP output

voltage, perform an initial calibration at a known, controlled

temperature. Then, use the following equation to extract

temperature information:

VTEMP

CO

CAL

DD

CAL

DD

TEMP

VTEMP

TC

T

T

V

V

V

V

T









































–

–

where:

output voltage.

controlled temperature.

Specifications section for the exact value.

Gain Control Mode

Gain control (GC) enable mode can be activated by switching

the GC pin to the VDD pin. In this mode, the AMR bridge

sensor amplitude outputs are compensated to reduce

temperature variation. This results in higher and controlled

output voltage levels, boosting system dynamic range and

easing the system design task. If the GC pin is left floating, a

weak pull-up resistor ensures that the GC mode is enabled as a

default condition. The GC mode can also be used as a sensor

self diagnostic by comparing the sine and cosine amplitude

outputs when enabled and disabled, such as radius check. In the

event that the radius does not change, it indicates a gross failure

in the IC.

Power-Down Mode

Power-down mode can be activated by switching the PD pin to

the VDD pin. Within this mode, the device shuts down and its

output pins are set to high impedance to avoid current

consumption across the load resistors. The VTEMP output is

connected to ground through a pull-down resistor. Power-down

pull-down resistor ensures that the device remains active if the

PD pin is left floating.