MA732 – 14-BIT, DIGITAL ANGLE SENSOR WITH ABZ & PWM OUTPUTS

MA732 Rev. 1.1

MonolithicPower.com

9

8/8/2022

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© 2022 MPS. All Rights Reserved.

OPERATION

Sensor Front-End

The magnetic field is detected with integrated

Hall devices located in the center of the package.

The angle is measured using the SpinaxisTM

method, which digitizes the direction of the field

directly

without

complex

arctangent

computations or feedback loop based circuits

(interpolators).

The SpinaxisTM method is based on phase

detection, and generates a sinusoidal signal with

a phase that represents the angle of the

magnetic field. The angle is then obtained by a

time-to-digital converter, which measures the

time between the zero crossing of the sinusoidal

signal and the edge of a constant waveform (see

Figure 2). The time-to-digital is the output from

the front-end to the digital conditioning block.

Top

– Sine Waveform

Bottom

– Clock of Time-to-Digital Converter

Figure 2: Phase Detection Method

The output of the front-end delivers a digital

number proportional to the angle of the magnetic

field at a rate of 1MHz in a straightforward, open-

loop manner.

Digital Filtering

The front-end signal is further treated to achieve

the final effective resolution. This treatment does

not add any latency in steady conditions. The

filter transfer function can be calculated with

Equation (1):

2

1 2 s

H(s)

(1

s)

+

=

+

(1)

Where

τ is the filter time constant related to the

cutoff frequency by

τ = 0.38 / fcutoff. See the

General Characteristics section on page 5 for the

value of fcutoff.

Sensor Magnet Mounting

The sensitive volume of the MA732 is confined

to a region less than 100µm wide, and has

multiple integrated Hall devices. This volume is

located horizontally and vertically within 50µm of

the center of the QFN package. The sensor

detects the angle of the magnetic field projected

in a plane parallel to t

he package’s upper

surface. This means that the only relevant

magnetic field is the in-plane component (X and

Y components) in the middle point of the

package.

By default, if looking at the top of the package,

the angle increases when the magnetic field

rotates clockwise. Figure 3 shows the zero angle

of the unprogrammed sensor, where the cross

indicates the sensitive point. Both the rotation

direction

and

the

zero

angle

can

be

programmed.

Figure 3: Detection Point and Default Positive

Direction

This type of detection provides flexibility for the

design of an angular encoder. The sensor only

requires the magnetic vector to lie essentially

within the sensor plane with a field amplitude of

at least 40mT. The MA732 can work with fields

smaller than 40mT, but the linearity and

resolution performance may deviate from the

specifications.

The most straightforward mounting method is to

place the MA732 sensor on the rotation axis of a

permanent

magnet

(e.g.

a

diametrically

magnetized

cylinder)

(see

Figure

4).

The

recommended magnet is a Neodymium alloy

(N35) cylinder with dimensions of Ø5x3mm,

inserted into an aluminum shaft with a 1.5mm air

gap between the magnet and the sensor