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

MA780 Rev. 1.2

MonolithicPower.com

25

8/30/2021

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Table 19: Threshold to Wake Up

THR[6:0]

Threshold (degrees)

0

0

1

1.41

2

2.81

…

…

127

178.59

128

180 (ND flag only at 180°)

129

181.41 (no ND flag)

…

…

255

358.59 (no ND flag)

Reference (REF)

The angle change is defined in relationship to a

reference angle. REF is a parameter that

controls this angle. The ND pin goes high when

the angle distance to REF exceeds the threshold.

REF is an absolute angle coded on 8 bits (see

Table 20).

Table 20: Change Detection Fixed Reference

REF[7:0]

Reference (deg)

0

0

1

1.41

2

2.81

…

…

255

358.59

To

detect

the

relative

motion

and

avoid

repeatedly asserting the ND signal when the

angle is outside the set threshold, update the

reference position (REF) in register 10 with the

current angle position each time the threshold is

crossed.

Turn Counting

The MA780 can count 16, 64, and 256 rotation

turns. The counter value is coded on M = 4, 6, or

8 bits by the MULT parameter (see Table 21).

The number of turns is indicated by the M bits on

the MSB side of the 16-bit output. As a

consequence, the angle information is shifted by

M bits, and the resolution is reduced by M bits,

as seen below:

MSB

LSB

MISO

Turn(M-1:0)

Angle(15:M)

The number of turns to count is set by

MULTI[1:0], and the value is stored in register 22.

When writing to this register, only modify bit[3]

and bit[4], and ensure that the other bits retain

their default value (see Table 8 on page 18).

Table 21: Turn Counting

MULTI[1:0]

Number of

Turns

M (Bit Used to

Count Turns)

0

0 (default)

0

1

16

4

2

64

6

3

256

8

The counter value is stored in the volatile

memory. When the MA780 is idle, the value is

maintained until the next angle update. When

updating the turn count, the sensor always

assumes that the angle increment is smaller than

180 degrees. This means that if the shaft turns

more than 180 degrees per idle time, the counter

goes backwards.

To prevent turn count errors, ensure that the

angle change during the idle time is always

below 180 degrees. When counting up, the

counter overflows back to zero after reaching its

maximum value for the specified number of bits

(M). A similar principle applies when counting

down from zero to the maximum value.

If power is removed from the sensor, the counter

always resets to zero. In normal operation, the

zero setting only affects the angle. The angle

does not reset the turn counter.