MA302 – 12-BIT, DIGITAL ANGLE SENSOR WITH ABZ & UVW OUTPUTS

MA302 Rev. 1.1

www.MonolithicPower.com

20

2/7/2020

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© 2020 MPS. All Rights Reserved.

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

reduced to recover an equal Hall signal for all

angles and suppress the error. The parameter

ETX and ETY controls in which direction the

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)

Equation (6) is plotted in Figure 17 and Table 11.

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 11: 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 18). k can be calculated

with Equation (7):

)

tan(

)

tan(

m

m

a

a

E

k





(7)

Figure 18: Error Curve in Side-Shaft

Configuration with BCT = 0

Some

examples

are

given

in

Table

11.

Alternatively, the k parameter can be obtained

from the graph of Figure 19.

-40

-20

0

20

40

0

50

100

150

200

250

300

350



m

rotor angle (deg)

2E