MA120 – ANGULAR SENSOR FOR BRUSHLESS MOTOR COMMUTATION

PRELIMINARY SPECIFICATIONS SUBJECT TO CHANGE

MA120 Rev. 1.2

www.MonolithicPower.com

11

7/25/2016

MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.

Preliminary Specifications Subject to Change

© 2016 MPS. All Rights Reserved.

Sensor

– Magnet Mounting

The sensitive volume of the MA120 is confined

in a region less than 100µm wide and has

multiple integrated Hall devices. This volume is

located both horizontally and vertically within

50µm of the center of the QFN package. The

sensor detects the angle of the magnetic field

projected in a plane parallel to the package’s

upper surface. This means that the only

relevant

magnetic

field

is

the

in-plane

component (X and Y components) in the middle

point of the package.

Rotation Direction

Looking

at the MagAlpha top, the angle

increases when the magnetic field rotates

clockwise. Figure 3 shows the zero angle of the

unprogrammed

MA120,

where

the

cross

indicates the sensitive point.

Figure 3: Zero Angle of Unprogrammed MA120

This type of detection provides flexibility for the

design of an angular encoder. The sensor only

requires the magnetic vector to lie essentially

within the sensor plane with an amplitude of at

least 30mT. Note that the MA120 can work with

fields smaller than 30mT, but the linearity and

resolution performance may deviate from the

specifications. The straightforward solution is to

place the MA120 sensor on the rotation axis of

a permanent magnet (i.e.: a diametrically

magnetized cylinder) (see Figure 4).

Figure 4: End-of-Shaft Mounting

Mounting and Power Supply Decoupling

For most applications, a single 100nF bypass

capacitor placed close to the supply pins

decouples the MA120 from power supply noise.

If

better decoupling

is required,

a larger

capacitor (i.e.: 1µF to 10µF) can be added in

parallel with the 100nF capacitor, and/or a

serial

resistor (i.e.: 10Ω) can be added on the

supply line.

Ensure that

the capacitor

is

connected with low impedance paths.

VFLASH needs to be supplied only when

flashing the memory. Otherwise, VFLASH can

remain unconnected (see Figure 5).

Figure 5: Connection for Supply Decoupling

The package

’s exposed pad can be soldered to

the PCB to ensure optimal electrical, thermal,

and

mechanical

conditions.

In

case

the

exposed pad is soldered, it is recommended to

connect the pad to ground electrically.

Sensor Front-End

The magnetic field is detected with integrated

Hall devices located in the center of the

package. The angle is measured using the

spinaxis method, which directly digitizes the

direction of the field without any arctangent

computation or feedback loop-based circuit

(interpolators, etc.).

The spinaxis method is based on phase

detection. It requires sensitive circuitry that

generates a sinusoidal signal with a phase that

represents the angle of the magnetic field. The

angle is then retrieved by a time-to-digital

converter, which counts the time between the

zero crossing of the sinusoidal signal and the

edge of a constant waveform (see Figure 6).

The digitized time is the front-end output.