MA704 – 10-BIT, DIGITAL ANGLE SENSOR WITH ABZ & UVW OUTPUTS
multiple integrated Hall devices. This volume is
located both 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 the 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.
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 Spinaxis
method, which digitizes the direction of the field
directly without complex arctangent computation
or feedback loop-based circuits (interpolators).
TM
TM
The Spinaxis method is based on phase
By default, when 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.
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 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 the rate of 1MHz in a straightforward and
open-loop manner.
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 30mT. Note that the MA704 can work
with fields smaller than 30mT, but the linearity
and resolution performance may deviate from
the specifications. The most straightforward
mounting method is to place the MA704 sensor
on the rotation axis of a permanent magnet (i.e.:
a diametrically magnetized cylinder) (see Figure
4). The recommended magnet is a Neodymium
alloy (N35) cylinder with dimensions Ø5x3mm
inserted into an aluminum shaft with a 1.5mm air
gap between the magnet and the sensor
(surface of package). For good linearity, the
sensor is positioned with a precision of 0.5mm.
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):
1 2s
(1s)2
H(s)
(1)
Where τ is the filter time constant related to the
cutoff frequency by: τ = 0.38/Fcutoff. See the
General Characteristics table on page 5 for the
value of Fcutoff.
Sensor – Magnet Mounting
The sensitive volume of the MA704 is confined
in a region less than 100µm wide and has
MA704 Rev. 1.0
9/27/2017
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