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

MA780 Rev. 1.2

MonolithicPower.com

8

8/30/2021

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The most straightforward mounting method is to

place the MA780 sensor on the rotation axis of a

permanent

magnet

(e.g.

a

diametrically

magnetized cylinder) (see Fig 5).

Figure 5: End-of-Shaft Mounting

The recommended magnet is a Neodymium

alloy (N35) cylinder with typical dimensions

(Ø5x3mm) inserted into an aluminum shaft with

a 1.5mm air gap between the magnet and the

sensor (surface of package). For good linearity,

the sensor should be positioned with a precision

of 0.5mm.

If the end-of-shaft position is not available, the

sensor can be positioned away from the rotation

axis of a cylinder or ring magnet (see Figure 6).

In this case, the magnetic field angle is no longer

directly proportional to the mechanical angle.

The MA780 can be adjusted to compensate for

this effect, and to recover the linear relation

between the mechanical angle and the sensor

output. With multiple pole-pair magnets, the

MA780 indicates multiple rotations for each

mechanical turn.

Figure 6: Side-Shaft Mounting

Power Modes

The MA780 has 3 power modes, described

below.

1. Active: The sensor runs without interruption,

and the current consumption is IACTIVE (see

the Electrical Characteristics section on page

4).

2. Idle: The sensor front end shuts down, and

only the SPI communication interface and

memory

blocks

work.

The

current

consumption is IIDLE (see the Electrical

Characteristics section on page 4).

3. Automatic

Sampling

Cycle

(ASC):

The

device

automatically

switches

between

active and idle mode.

Table 1: Supply Current with Different Modes

Power Mode

Average Supply Current

(IAVERAGE)

Active

IACTIVE

ASC

IIDLE < IAVERAGE< IACTIVE

Idle

IIDLE

Figure 7 shows the timing of a power cycle.

Active

Idle

tACTIVE

tCYCLE

tIDLE

Figure 7: Timing of a Power Cycle

By combining these 3 power modes, the MA780

can be operated in different ways.

Continuous Automatic Sampling Cycle (ASC)

In ASC mode, the on-chip, low-power clock

continuously runs to control the sensor's power

cycle, according to the active time and cycle time

stored in the register.

In the minimum configuration (when ASC mode

is set by the internal register), the MA780 only

has SPI connections. The master device can

communicate with the MA780 at any time, the

same way that it does in active mode (see Figure

8). The difference is that in the minimum

configuration, the average power consumption is

low, and the refresh rate is determined by the

TCYC parameter.

MA

SPI

Master

Figure 8: Minimum Configuration for Continuous

ASC

The SPI output updates at the end of the active

period (see Figure 9).