MagAlpha
MA700
Angular Sensor for Position Control with
Side-Shaft Positioning Capability
Key features
11 bit resolution absolute angle encoder
500 kHz refresh rate
Ultra low latency: 3 µs
Serial interface for data readout and settings
10 bit incremental output (A,B,Z)
Built-in linearization for side-shaft mounting
7.5 mA supply current
QFN-16 3x3mm Package
General Description
The MagAlpha MA 700 is a robust contactless angle
encoder. The IC detects the absolute angular position
of a permanent magnet, typically a diametrically
magnetized cylinder attached to the rotor. The
MagAlpha is an extremely fast acquisition and
processing sensor, allowing accurate angle
measurement at speeds from 0 to 120’000 RPM.
Since the measurement is spatially confined, the user
has flexibility in terms of magnet shapes and
configurations. This can help relaxing mechanical
tolerances and, in case the end of shaft position is not
available, the MagAlpha 700 can also operate away
from the axis of rotation (“side-shaft” mounting).
Figure 1: Functional Block Diagram
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MA700
Angular Sensor for Position Control with
Side-Shaft Positioning Capability
1. Specifications
TABLE 1 OPERATING CONDITIONS
Parameters
Symbol
Min
Typ
Max
Supply voltage
VDD
3.0
3.3
3.6
V
Supply current
Isup
5.7
6.6
8.0
mA
Vflash
3.6
3.8
V
Supply voltage for OTP flashing
Supply current for OTP flashing
(1)
Unit
Iflash
50
100
mA
Operating temperature
Top
-40
125
°C
Applied magnetic field
B
30
150
mT
(1)
75
See section 11 for more details about the supply circuit for OTP flashing.
TABLE 2 SENSOR OUTPUT SPECIFICATIONS
Measurement conditions: VDD = 3.3 V, 50 mT < B < 100 mT, Temp = -40 .. +125°C, unless otherwise noted
Parameters
Min
Typ
Max
2
3
ms
+/- 0.7
+/- 1.5
+/-2.5
deg
Temperature induced
+/-0.005
+/-0.008
+/-0.05
deg/°C
Magnetic field induced
-0.005
-0.01
-0.025
deg/mT
Voltage supply induced
0.0007
0.001
0.005
deg/mV
Power up time
INL
Unit
Remark
Output drift
Absolute output - serial
Data output length
16
Refresh rate
500
Latency
Resolution (3 noise level)
16
bit
520
550
kHz
2
3
4
µs
10.5
11.0
11.5
bit
1024
edge/revol
.
Incremental output
Resolution
Jitter
1024
% of a
period
10
Hysteresis
0.35
deg
Digital I/O
Threshold voltage High
1.75
V
Threshold voltage Low
1.05
V
Rising edge slew rate
0.7
V/ns
CL = 50 pF
Falling edge slew rate
0.7
V/ns
CL = 50 pF
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MA700
Angular Sensor for Position Control with
Side-Shaft Positioning Capability
2. Timing of the Serial Interface
The data link is a 4-wire serial bus, conmplying to the Serial Peripheral Interface (SPI) usual convention shown in Table
3 and Table 4.The MagAlpha sensor operates as slave. During one transmission a 16 bit word can be simultaneously
sent to the sensor (MOSI pin) and received from the sensor (MISO pin). Note that it is possible to receive 24 bits of data
(16 bits for the angle and 8 bits for a time index). See section 10 “Output Signals” for details.
Figure 2: SPI Timing Diagram
TABLE 3 SPI SPECIFICATION
TABLE 4 SPI STANDARD
SCLK idle state
High
CPOL
1
SCLK readout edge
Rising
CPHA
1
CS idle state
High
MODE
3
Data order
MSB first
DORD
0
TABLE 5 SPI TIMING
Parameter
Description
Min
Max
tidle
Time between two subsequent transmissions
20
ns
tcsL
Time between CS falling edge and SCLK falling edge
25
ns
tsclk
SCLK period
40
ns
tsclkL
Low level of SCLK signal
20
ns
tsclkH
High level of SCLK signal
20
ns
tcsH
Time between SCLK rising edge and CS rising edge
25
ns
tMOSI
Data input valid to SCLK reading edge
15
ns
tMISO
SCLK setting edge to data output valid
15
Unit
ns
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MA700
Angular Sensor for Position Control with
Side-Shaft Positioning Capability
3. Registers
TABLE 6 REGISTER MAP
Register address
No
Hex
Bin
3
0x3
0011
BCT(7:0)
4
0x4
0100
Z(11:4)
5
0x5
0101
0
0
ETY
ETX
9
0x9
1001
-
-
F5
F4
Bit 7 MSB
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0 LSB
Z(3:0)
F3
-
-
-
TABLE 7 PROGRAMMING PARAMETERS
Symbol
Number of
bit
BCT
8
Z
12
Enable Trimming X
ETX
1
Enable Trimming Y
ETY
1
Fn
1
Parameters
Bias Current Trimming
Zero setting
Flash register n
Brief description
See
table
For side-shaft configuration: reduce the Hall
device bias current of X- and/or Y-axis
Set the zero position
When enabled, the X-axis bias current is
trimmed by the quantity BCT
When enabled, the Y-axis bias current is
trimmed by the quantity BCT
Flash the content of register number n
9
11
10
10
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MA700
Angular Sensor for Position Control with
Side-Shaft Positioning Capability
4. Pin Configuration
TABLE 8 PIN FUNCTIONS
Figure 3: QFN-16 Top View
No
Name
Function
1
N/C
-
2
B
B
(incremental output)
3
Z
Z
(incremental output)
4
MOSI
5
CS
6
A
7
MISO
Data out (serial)
8
GND
Ground
9
N/C
-
10
N/C
-
11
N/C
-
12
SCLK
Clock (serial)
13
VDD
3.3 V supply
14
N/C
-
15
N/C
-
16
VFLASH
Data in (serial)
Chip Select (serial)
A
(incremental output)
3.6 V supply for OTP flashing
5. Sensor – Magnet Mounting
The sensitive volume of the MA 700 is confined in a
region less than 100 µm wide and consists of multiple
integrated Hall devices. This volume is located, with a
precision of 50 m in the center of the QFN package,
both horizontally and vertically. The sensor detects the
angle of the magnetic field projected in a plane parallel
to the package upper surface. It means that the only
magnetic field that matters is the in-plane component
(X and Y components) in the package middle point.
This detection mode gives flexibility for the design of
an angular encoder: all the sensor needs is that the
magnetic vector lies essentially within the sensor plane
and that its amplitude is comprised between 30 and 150
mT. Note that the MA 700 does work with smaller than
30 mT fields, but the linearity and resolution
performance may deviate from the specifications (table
2). The straightforward solution is to place the MA 700
sensor on the rotation axis of a permanent magnet for
instance a cylinder diametrically magnetized (see
Figure 4).
Figure 5: Side-Shaft Mounting
Figure 4: End-of-Shaft Mounting
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MA700
Angular Sensor for Position Control with
Side-Shaft Positioning Capability
When 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 5). In this case
the magnetic field angle is not directly proportional to
the mechanical angle anymore. The MA 700 can be
adjusted to compensate this effect and recover the
linear relation between the mechanical angle and the
sensor output. With multiple pole pairs, the MA 700
will indicate multiple rotations for each mechanical
turn.
6. Power Supply Decoupling
For most applications, a single 100 nF bypass capacitor
placed close to the supply pins sufficiently decouples
the MA 700 from noise of the power supply. If better
decoupling is required, a larger capacitor (10 µF) can
be added in parallel with the 100 nF, and/or a resistor
(10) can be added between the supply line and the
capacitor node.
In any case, make sure that the connection between the
MA 700 ground and the power supply ground has a
low impedance, in order to avoid noise transmitted
from the ground.
VFLASH needs to be supplied only when flashing the
memory. Otherwise the VFLASH pin can remain
unconnected or grounded (see Figure 6).
Figure 6: Connection for Supply Decoupling
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-todigital converter, which counts the time between the
zero crossing of the sinusoidal signal and the edge of a
constant waveform (see Figure 7). The digitized time is
the front-end output.
Figure 7: 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
compensated, resulting in the stability displayed in
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MA700
Angular Sensor for Position Control with
Side-Shaft Positioning Capability
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.
Side-Shaft
The X-axis or the Y-axis bias current can be reduced in
order to recover an equal Hall signal for all angles and
therefore suppress the non-linearity. The current
reduction is set by the parameter Bias Current
Trimming BCT(7:0), which is an integer from 0 to 255.
For an optimum compensation the radial axis should be
reduced by the quantity:
The default current biasing of the Hall devices can be
adjusted by programming in order to accommodate low
field or compensate non-linearities inherent to sideshaft configurations.
TABLE 9 EXAMPLE OF OPTIMUM BCT SETTING
BCT(7:0)
Figure 8: Hall Devices Biasing Diagram
Magnet ratio k
0
1
1
1.003
…
…
128
1.50
…
…
255
3.00
From the dot printed on the package it is possible to
know whether the radial field is detected by the sensor
X or Y component (see Figure 10).
In case the MA700 gets mounted in side-shaft configuration, the relation between the field angle and the
mechanical angle is not directly linear anymore. This
effect is related to the fact that the tangential magnetic
field is usually smaller than the radial field. We define
the field ratio as:
Figure 10: Package Top View with X and Y Axes
,
where
, respectively
, is the maximum radial,
respectively tangential, magnetic field (see Figure 9).
First the user must determine which axis needs to be
reduced (see the qualitative field distribution around a
ring in Figure 9). For instance, with the arrangement
depicted in Figure 8, the X-axis should be reduced.
Then the parameter ETX or ETY can be set. Note that
if both ETX and ETY are set to 1 the current bias will
be reduced in both directions the same way, i.e.
without side-shaft correction.
TABLE 10 ETX AND ETY
ETX
Enable trimming the X axis
0
Disabled
1
Enabled
Figure 9: Side-Shaft Field
ETY
The ratio k depends on the magnet geometry and the
distance to the sensor.
0
Disabled
1
Enabled
Enable trimming the Y axis
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MA700
Angular Sensor for Position Control with
Side-Shaft Positioning Capability
8. Digital Signal Conditioning
Digital Filtering
TABLE 11 ZERO POSITION
Advanced digital filtering allows improving the
resolution without adding latency. The principle is to
measure the rotation speed over the last 512 data points
in addition to the angular position to provide an
evaluation of the present position with the best possible
accuracy. This principle gives a lag-free position at
constant speed.
Z(11:0)
Zero position
0
0
1
0.088
…
…
4095
359.912
(deg)
Zero setting
The zero position of the MagAlpha,
programmed with 12 bit of resolution.
streamed out,
, is given by:
, can be
The angle
Rotation direction
Looking at the MagAlpha top, the angle increases
when the magnetic field rotates clockwise.
,
where
is the raw angle, out of the front-end. The
parameter Z(11:0), which is 0 by default, determines
(see Table 18). This setting is valid for all output
formats: SPI, ABZ and UVW.
9. Programming the MA700
The MA700 incorporates 3 programmable registers.
Each register has 8 bit of memory. When the MA700 is
powered up, each of these 3 x 8 bit of memory are 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.
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 a 4-bit register
address 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
0 0 1 0
reg. address
MSB
value
Once the command is sent, it will immediately be
effective and will affect the next data sent from the
MagAlpha.
Read back the register content
It might be helpful to check the content of a register,
for instance to verify that the programming was
successful. The user must send the REGISTER READ
command: 0001, then the 4-bit address of the register
under test. The last 8-bit of the stream will be ignored.
The user can send for instance 0000 0000:
command
0 0 0 1
reg. address
x x x x
value
LSB
0 0 0 0 0 0 0 0
MSB
LSB
The MagAlpha response is within the same
transmission. In the first byte (simultaneous to the 4-bit
READ command and the 4-bit address), the MagAlpha
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MA700
Angular Sensor for Position Control with
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sends the 8 MSB of the measured angle A(15:8). The
second byte is the content of the register under test.
After this transmission the MagAlpha will continue
delivering the usual 16-bit angles A (15:0).
command
0 0 0 1
reg. address
0 1 0 0
value
LSB
0 0 0 0 0 0 0 0
MSB
Simultaneously the MagAlpha replies:
Example
To check the content of the register 4 (0100), which
contains the 8 MSB’s of the zero setting, send the data:
Angle out
A(15:12)
A(11:8)
MSB
value
Z(11:4)
LSB
10. Output Signals
The raw data coming out of the conditioning blocks is
an absolute angle, between 0 and 360 deg. This angle is
coded on 16 bits, depending on the value of AF. The
absolute output is sent out digitally as serial data. The
other outputs, ABZ or UVW, are constructed from the
absolute angles.
Absolute - Serial
The bit order of the transmitted data is MSB first, LSB
last. The timing requirements are indicated in section 3.
Every 2µs a new data is transferred into the output
buffer. The master device connected to the MagAlpha
triggers the reading by pulling the CS down. When a
falling edge of the CS signal occurs, the data remains
in the output buffer until the CS signal returns to
logic 1. As the CS is low, the master can read the data
by sending clock pulses with a maximum frequency of
25 MHz. There is not any minimum frequency or
timeout. See Figure 11 for a simple reading of 16 bit
data.
MagAlpha provides an 8-bit angle without ambiguity
over 360 deg.
MSB
LSB
A(15:8)
If the master triggers the reading faster than the refresh
rate the MagAlpha may send several times the same
data point.
In some applications it is helpful to know how many
data updates occurred between two successive readouts
or if the same data points was read more than once. For
this purpose the user can read an 8-bit index attached to
the data .It allows keeping track of the precise time of
measurement without the need of precisely controlling
the readout time. This index runs from 0 to 255 and is
incremented by 1 each time the output buffer is
refreshed. Using the index the user can detect a double
reading of the same data (same index), or how many
data points were skipped.
For reading the 8-bit index the master has to send
16 + 8 = 24 clock pulses (see Figure 12).
Figure 11: Timing Diagram for Simple SPI Readout
A full reading requires 16 clock pulses. The MA700
delivers:
MSB
LSB
A(15:8)
A(7:0)
Figure 12: Timing Diagram for SPI Angle + Index Readout
In case the user needs less resolution, since the MSB is
sent first, he can read the angle by sending less than 16
pulses. For instance by sending only 8 pulses, the
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MA700
Angular Sensor for Position Control with
Side-Shaft Positioning Capability
Incremental - ABZ
With the ABZ output the MA700 emulates a 10-bit
incremental encoder, such as an optical encoder,
providing logic pulses in quadrature (see Figure 13).
Compared to A, the signal B is shifted by a quarter of
pulse period. Over one revolution the A signal pulses
256 times. It makes 1024 edges per revolution. The
signal Z (“Zero” or “Index”) raises only once per turn,
at the zero angle position.
Figure 13 : ABZ Output during Rotation
11. OTP Programming
The One-Time-Programmable (OTP) memory can
permanently store the content of the programmable
registers. The OTP memory is made of poly-silicon
fuses. By activating the “flash” command the content
of the entire register will be stored in the OTP memory.
The flash command consists in setting some bits
(named Fn, where n is the register number) in the
register 9. When the bit Fn is set, the register n is
stored permanently. Important: the user can flash
only one register at the time. It is possible to operate
the MagAlpha without flashing the registers.
at power up will always be the same. After flashing the
registers content cannot be modified anymore.
Flashing procedure
Prior to flashing, it is recommended to test the
MagAlpha with the new settings and verify the
performance of the sensor.
Once satisfied, the user can proceed with the flashing:
-
-
Send the parameter to the register, and read
back for verification.
Tie the VFLASH pin to 3.6 V. Note: it is
possible to supply both VDD and VFLASH
with the same 3.6 V source.
In the register 9, set the bit corresponding to
the register to be flashed.
Untie the VFLASH pin
Then switch off and on and check by reading back the
register content.
Example: set & flash the zero position at 50 deg
Figure 14: Circuit for Flashing
Note: permanently storing the zero position requires to
burn two registers, 4 and the 5.
The burning of the fuses during the flash process is
irreversible: once a register is flashed the default values
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MA700
Angular Sensor for Position Control with
Side-Shaft Positioning Capability
1.
2.
Convert into binary: within a resolution of 12
bits, 50 deg is the binary number
001000111000 (49.92 deg).
Store the 8 MSB (00100011) of the zero
position into register 4:
command
0 0 1 0
3.
reg. address
0 1 0 0
value
LSB
0 0 1 0 0 0 1 1
value
LSB
0 0 0 0 1 0 0 0
MSB
MSB
reg. address
0 1 0 0
value
LSB
0 0 0 0 0 0 0 0
MSB
If the programming was correct the MagAlpha
replies with the register 4 content:
Angle out
A(15:12)
A(11:8)
value
LSB
0 0 1 0 0 0 1 1
MSB
Then store the 4 LSB (1000) of the zero
position into the 4 LSB of register 5:
command
0 0 1 0
5.
Angle out
A(15:12)
A(11:8)
6.
Connect the VFLASH pin to 3.6 V
7.
Flash register 4:
Read back the register 4
command
0 0 0 1
4.
The MagAlpha returns:
reg. address
0 1 0 1
value
LSB
0 0 0 0 1 0 0 0
MSB
command
0 0 1 0
8.
value
LSB
0 0 0 1 0 0 0 0
MSB
Flash register 5:
command
0 0 1 0
9.
reg. address
1 0 0 1
reg. address
1 0 0 1
value
LSB
0 0 1 0 0 0 0 0
MSB
Disconnect the VFLASH pin from 3.6 V.
10. Turn the MagAlpha off and on, and read back
the registers 4 and 5 to verify that the flashing
was successfully accomplished (steps 3 & 5).
Read back the register 5:
command
0 0 0 1
reg. address
0 1 0 1
value
LSB
0 0 0 0 0 0 0 0
MSB
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MA700
Angular Sensor for Position Control with
Side-Shaft Positioning Capability
12. Typical Characteristics
Measurement conditions: VDD = 3.3V, Temp = 25°C,
unless otherwise noted.
Figure 15: Error Curve at Different Magnetic Fields. The INL is
the Maximum Value of this Curve.
Figure 16: Resolution in Bits vs. Angle at Different Magnetic
Fields.
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MA700
Angular Sensor for Position Control with
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13. Package Dimensions
Package: Plastic Quad Flatpack No-lead QFN-16 3x3mm
NOTES:
1.
All dimensions are in mm
2.
Package dimensions does not include mold flash, protrusions, burrs or metal smearing
3.
Coplanarity shall be 0.08
4.
Compliant with JEDEC MO-220
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MA700
Angular Sensor for Position Control with
Side-Shaft Positioning Capability
14. Ordering Information
Part Number
Package
Free Air Temperature (TA)
MA700GQ
QFN 3x3mm
-40° to 125°
* For Tape & Reel, add suffix –Z (e.g. MA700GQ–Z).
Appendix A: Definitions
Resolution (3 noise level)
The smallest angle increment distinguishable from the noise. Here the resolution
is defined as 3 times , the standard deviation in degrees, taken over 1000 data
points at a constant position. The resolution in bits is obtained with:
6 .
Refresh rate
Rate at which new data points are stored in the output buffer.
Latency
The time between the data ready at the output and the instant at which the shaft
passes that position. The lag in degrees is
, where is the
angular velocity in deg/s.
Power up time
Starting at power up, time until the sensor delivers valid data.
Integral Non-Linearity (INL)
Maximum deviation between the sensor output and the best line fit.
400
sensor out (deg)
350
300
lag
250
ideal
sensor output
200
150
INL
100
0
sensor out
best straight fit
resolution
( ± 3 )
50
0
100
200
300
400
500
600
700
rotor position (deg)
Figure A1: Absolute Angle Errors
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MA700
Angular Sensor for Position Control with
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Jitter
For the incremental output maximum fluctuation of the angular position of the
raising edges.
Overall reproducibility
Maximum variation between two readings, successive or not, of the same shaft
position at a fixed magnetic field over the complete temperature range.
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The information provided by Monolithic Power Systems, Inc. in this document is believed to be correct. However MPS reserves the right, without
further notice, (i) to change the product specification and/or the information in this document and (ii) to improve reliability, functions and design of
the product and (iii) to discontinue or limit production or distribution of any product version.
Monolithic Power Systems, Inc. does not assume any liability arising out of any application or use of any product or information, including without
limitation consequential or incidental damages. All operating parameters must be validated for each customer's application by customer's technical
experts. Recommended parameters can and do vary in different applications.
Devices sold by MPS are covered by patents and patent applications. By this publication MPS does not assume responsibility for patent infringements
or other rights of third parties which may result from its use.
Monolithic Power Systems, Inc. | Gland, Switzerland | Tel: +41 22 364 63 50 | euroinfo@monolithicpower.com | www.sensimatech.com
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2014 Monolithic Power Systems. All Rights
Reserved. MA700 Rev 1.0 September 2014
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