MA780 – 8-BIT TO 12-BIT LOW-POWER ANGLE SENSOR

MA780 Rev. 1.2

MonolithicPower.com

19

8/30/2021

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REGISTER SETTINGS

Zero Setting

The zero position of the MA780 (a0) can be

configured with 16 bits of resolution. The angle

outputted by the MA780 (aOUT) can be calculated

with Equation (2):

OUT

RAW

0

a

= a

- a

(2)

Where aRAW is the raw angle provided by the

MA780 front end.

The parameter Z[15:0] is the zero-angle position

coded on 16 bits (see Table 10).

Table 10: Zero Setting Parameter

Z[15:0]

a0 (deg)

0

0

1

0.005

2

0.011

…

…

65534

359.989

65535

359.995

Rotation Direction

When looking at the top of the package, the

angle increases when the magnetic field rotates

clockwise (CW) by default (see Figure 25).

Figure 25: Positive Rotation Direction of the

Magnetic Field

Table 11 lists how to designate the rotation

direction.

Table 11: Rotation Direction Parameter

RD

Positive Direction

0

Clockwise (CW)

1

Counterclockwise (CCW)

BCT Settings (Bias Current Trimming)

Side Shaft

When the MA780 is mounted on the side of the

magnet, the relationship between the field angle

and mechanical angle is no longer linear. This

effect is related to the fact that the tangential

magnetic field is usually smaller than the radial

field. Calculate the field ratio (k) with Equation (3):

RAD

TAN

k = B

/B

(3)

Where BRAD and BTAN are the maximum radial

and tangential magnetic fields (see Figure 26).

BRAD

BRAD

BTAN

BTAN

Figure 26: Side-Shaft Field

The k ratio depends on the magnet geometry

and the distance to the sensor. If the k ratio does

not equal 1, the sensor output response is

nonlinear with respect to the mechanical angle.

The error curve has the shape of a double sine

wave, where E is the amplitude of this error (see

Figure 27).

-40

-20

0

20

40

0

50

100

150

200

250

300

350



m

rotor angle (deg)

2E

aM

Rotor Angle (deg)

2E

Figure 27: Error Curve in Side-Shaft

Configuration (BCT = 0)

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 parameters

ETX and ETY control the direction in which

sensitivity is reduced. The current reduction is

set by the bias current trimming parameter

(BCT[7:0]), which is an integer from 0 to 255.