MA710 – 12-BIT, DIGITAL ANGLE SENSOR WITH ABZ & PWM OUTPUTS

MA710 Rev. 1.0

www.MonolithicPower.com

19

9/27/2017

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© 2017 MPS. All Rights Reserved.

REGISTER SETTINGS

Zero Setting

The zero position of the MagAlpha (a0) can be

programmed with 16 bits of resolution. The

angle streamed out by the MagAlpha (aout) is

given by Equation (2):

0

a

a

a

raw

out





(2)

Where araw is the raw angle provided by the

MagAlpha front end.

The parameter Z(15:0), which is zero by default,

is the complementary angle of the zero setting.

In decimals, it can be written as shown in

Equation (3):

)

0

:

15

(

2

16

0

Z

a





(3)

Table 10 shows the zero setting parameter.

Table 10: Zero Setting Parameter

Z(15:0)

Zero pos.

a0 (16 bit dec)

Zero pos.

a0 (deg)

0

65536

360.000

1

65535

359.995

2

65534

359.989

…

…

…

65534

2

0.011

65535

1

0.005

Example

To set the zero position to 20 degrees, the

Z(15:0)

parameter

shall

be

equal

to the

complementary angle and can be calculated

with Equation (4):

61895

2

deg

360

deg

20

2

)

0

:

15

(

16

16







Z

(4)

In binary, it is written as 1111 0001 1100 0111.

Table 11 shows the content of the registers 0

and 1.

Table 11: Register 0 and 1 Content

Reg Bit7 Bit6 Bit5 Bit4 Bit3 Bit2 Bit1 Bit0

0

1

1

0

0

0

1

1

1

1

1

1

1

1

0

0

0

1

Rotation Direction

By default, when looking at the top of the

package,

the

angle

increases

when

the

magnetic field rotates clockwise (CW) (see

Figure 18 and Table 12).

Figure 15: Positive Rotation Direction of the

Magnetic Field

Table 12: Rotation Direction Parameter

RD

Positive Direction

0

Clockwise (CW)

1

Counterclockwise (CCW)

BCT Settings (Bias Current Trimming)

Side Shaft

When the MA710 is mounted on the side of the

magnet, the relation between the field angle

and the mechanical angle is no longer directly

linear. This effect is related to the fact that the

tangential magnetic field is usually smaller than

the radial field. Define the field ratio k with

Equation (5):

tan

/ B

B

k

rad



(5)

Where Brad and Btan are the maximum radial and

tangential magnetic fields (see Figure 19).

Figure 16: Side-Shaft Field

The ratio k depends on the magnet geometry

and the distance to the sensor. Having a k ratio

different than one results in the sensor output

response not being linear with respect to the

mechanical angle. Note that the error curve has

the shape of a double sinewave (see Figure 21).

E is the amplitude of this error.