MA120GQ-Z Datasheet, PDF (7/14 Pages) MPS Industries, Inc. – Angular Sensor for 3-Phase Brushless Motor Commutation

MA120
Angular Sensor for 3-Phase Brushless Motor
Commutation
7. Sensor Front-End
The magnetic field is detected with integrated Hall
devices located in the package center. The particularity
of this sensor is that the angle is measured using the
spinaxis method which directly digitizes the direction
of the field without any ATAN computation or any
feedback loop based circuit (interpolators, etc.).
The spinaxis method is based on phase detection. It
requires a sensitive circuitry generating a sinusoidal
signal whose phase 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.
compensated, resulting in the stability displayed in
Table 2. In short, the front-end delivers in a
straightforward and open loop manner a digital number
proportional to the angle of the magnetic field at the
rate of 500 kHz
Zero setting
The zero position of the MagAlpha, , can be
programmed with 8 bit of resolution. The angle
streamed out, , is given by:
,
where is the raw angle, out of the front-end. The
parameter Z(7:0), which is 0 by default, determines
(Table 11). This setting is valid for all output formats:
SPI and UVW.
Figure 6: Phase Detection Method. Top: Sine Waveform.
Bottom: Clock of Time-to-Digital Converter.
Looking further down the treatment chain, it is crucial
that the signal treatment does not add unwanted phase
shifts. For this purpose the MagAlpha incorporates an
architecture where these shifts are automatically
8. Programming the MA120
The MA120 incorporates one programmable register.
(8 bit of memory). When the MA120 is powered up,
each 8 bit of memory is set to zero, unless the register
was previously stored in the One-Time-Programmable
(OTP) memory. It means that during startup, the
content of the OTP memory is copied to the registers.
Once flashed the register content cannot be modified
anymore.
TABLE 11 ZERO POSITION
Z(11:0)
0
1
…
255
Zero position (deg)
0
1.41
…
358.59
In order to set the content of a register, the user must
send a digital stream composed of the 4-bit REGISTER
WRITE command (0010), followed by the 4-bit
register address (0100) and the 8-bit value to be sent to
the register. The data stream, sent through the MOSI
wire, is therefore 16 bits long:
command reg. address MSB
value
LSB
0010 0100
Monolithic Power Systems, Inc. | Gland, Switzerland | Tel: [phone] | [e-mail] | www.sensimatech.com
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Reserved. MA700 Rev 1.0 September 2014
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