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

MA710 Rev. 1.0

www.MonolithicPower.com

20

9/27/2017

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© 2017 MPS. All Rights Reserved.

The X-axis or the Y-axis bias current can be

reduced by programming in order to recover an

equal Hall signal for all angles and therefore

suppress the error. The parameter ETX and

ETY controls the direction in which sensitivity is

reduced. The current reduction is set by the

parameter bias current trimming BCT(7:0),

which is an integer from 0 to 255.

In side-shaft configuration (i.e.: the sensor

center is located beyond the magnet outer

diameter), k is greater than 1. For optimum

compensation, the sensitivity of the radial axis

should

be

reduced

by

setting

the

BCT

parameter as shown in Equation (6):











 



k

BCT

1

1

258

)

0

:

7

(

(6)

The graph in Figure 20 shows the optimum

BCT value for a particular k ratio.

0

50

100

150

200

1

1.5

2

2.5

3

3.5

4

4.5

5

k

Figure 17: Relation between the k Ratio and the

Optimum BCT to Recover Linearity

Table 13 shows some typical BCT values.

Table 13: Example of BCT Settings

E (deg)

Magnet Ratio k

BCT(7:0)

0

1.0

0

11.5

1.5

86

19.5

2.0

129

25.4

2.5

155

30.0

3.0

172

33.7

3.5

184

36.9

4.0

194

39.5

4.5

201

41.8

5.0

207

Determining k with the MagAlpha

It is possible to deduce the k ratio from the error

curve obtained with the default BCT setting

(BCT = 0). For this purpose, rotate the magnet

over one revolution and record the MagAlpha

output. Then plot the error curve (the MagAlpha

output minus the real mechanical position vs

the real mechanical position) and extract two

parameters: the maximum error E and the

position of this maximum with respect to a zero

crossing am (see Figure 21). k can be calculated

with Equation (7):

)

tan(

)

tan(

m

m

a

a

E

k





(7)

Figure 21: Error Curve in Side-Shaft

Configuration with BCT = 0

Some

examples

are

given

in

Table

13.

Alternatively, the k parameter can be obtained

from the graph of Figure 22.

-40

-20

0

20

40

0

50

100

150

200

250

300

350



m

rotor angle (deg)

2E