MAQ473

– 9-BIT TO 14-BIT, AUTOMOTIVE ANGLE SENSOR W/ ABZ & PWM OUTPUTS

MAQ473 Rev. 1.0

MonolithicPower.com

21

5/12/2021

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© 2021 MPS. All Rights Reserved.

The X-axis and Y-axis bias currents can be

reduced by programming in order to recover an

equal Hall signal for all angles, and therefore

suppress the error. Parameter ETX and ETY

control the direction in which sensitivity is

reduced. The current reduction is set by the

parameter

bias

current

trimming

register,

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

’s outer

diameter), k is greater than 1. For optimum

compensation, the sensitivity of the radial axis

should

be

reduced

by

setting

the

BCT

parameter, calculated with Equation (6):









1

BCT[7 : 0] = 258 1

k

(6)

Figure 21 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 21: Relation between the k Ratio and the

Optimum BCT to Recover Linearity

Table 14 shows some typical BCT values.

Table 14: 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). Rotate the magnet more than one

revolution and record the output. Next, plot the

error

curve

(the

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 22). k can be calculated with

Equation (7):

M

M

tan(E + a )

k=

tan(a )

(7)

-40

-20

0

20

40

0

50

100

150

200

250

300

350



m

rotor angle (deg)

2E

aM

Rotor Angle (deg)

2E

Figure 22: Error Curve in Side-Shaft

Configuration with BCT = 0

Table

14

provides

some

examples.

Alternatively, the k parameter can be obtained

using Figure 23.

1

1.5

2

2.5

3

3.5

4

4.5

5

0

5

10

15

20

25

30

35

40

E (deg)

Figure 23: Relation between the Error Measured

with BCT = 0 and the Magnet Ratio k