ams AS5311 High resolution magnetic linear encoder Datasheet

AS5311
Data Sheet
AS5311
Preliminary Data Sheet
High Resolution Magnetic Linear Encoder
1 General Description
The AS5311 is a contactless high resolution magnetic
linear encoder for accurate linear motion and off-axis
rotary sensing with a resolution down to <0.5µm. It is
a system-on-chip, combining integrated Hall elements,
analog front end and digital signal processing on a
single chip, packaged in a small 20-pin TSSOP
package.
A multi-pole magnetic strip or ring with a pole length
of 1.0mm is required to sense the rotational or linear
motion. The magnetic strip is placed above the IC at a
distance of typ. 0.3mm.
The absolute measurement provides instant indication
of the magnet position within one pole pair with a
resolution of 488nm per step (12-bit over 2.0mm).
This digital data is available as a serial bit stream and
as a PWM signal.
Furthermore, an incremental output is available with a
resolution of 1.95 µm per step. An index pulse is
generated once for every pole pair (once per
2.0mm).The travelling speed in incremental mode is
up to 650mm/second.
An internal voltage regulator allows the AS5311 to
operate at either 3.3 V or 5 V supplies.
Depending on the application the AS5311 accepts
multi-pole strip magnets as well as multi-pole ring
magnets, both radial and axial magnetized (see
Figure 1 and Figure 3).
The AS5311 is available in a Pb-free TSSOP-20
package and qualified for an ambient temperature
range from -40°C to +125°C.
2 Key Features
ƒ
Two 12-bit digital absolute outputs :
- Serial interface and
- Pulse width modulated (PWM) output
ƒ
Incremental output with Index
ƒ
“red-yellow-green” indicators monitor magnet
placement over the chip
3 Applications
ƒ
Micro-Actuator feedback
ƒ
Servo drive feedback
ƒ
Robotics
ƒ
Replacement of optical encoders
Figure 1: AS5311 with Multi-pole Magnetic Strip
for Linear Motion Sensing
Figure 2: Block Diagram of AS5311
VDD3V3
MagINCn
MagDECn
VDD5V
PWM
Sin
Ang
Cos
Mag
DO
CSn
CLK
A
B
AS5311
Index
Prog
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AS5311
Data Sheet
Figure 3: AS5311 with Multi-pole Ring Magnets for Off-axis Rotary Motion Sensing
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AS5311
Data Sheet
4 Table of Contents
1
General Description ...................................................................................................................... 1
2
Key Features ................................................................................................................................ 1
3
Applications.................................................................................................................................. 1
4
Table of Contents ......................................................................................................................... 3
5
Pinout .......................................................................................................................................... 5
5.1
Pin Assignments ..................................................................................................................... 5
5.2
Pin Description ....................................................................................................................... 5
6
Electrical Characteristics............................................................................................................... 6
6.1
Absolute Maximum Ratings ..................................................................................................... 6
6.2
Operating Conditions .............................................................................................................. 7
6.3
DC Characteristics for Digital Inputs and Outputs ..................................................................... 7
6.3.1
CMOS Schmitt-Trigger Inputs: CLK, CSn (CSn = internal Pull-up) ....................................... 7
6.3.2
CMOS Output Open Drain: MagINCn, MagDECn ................................................................ 7
6.3.3
CMOS Output: PWM ......................................................................................................... 7
6.3.4
Tristate CMOS Output: DO ................................................................................................ 8
6.4
Magnetic Input Specification.................................................................................................... 8
6.5
Electrical System Specifications .............................................................................................. 8
6.6
Timing Characteristics ............................................................................................................ 9
7
6.6.1
Synchronous Serial Interface (SSI) .................................................................................... 9
6.6.2
Pulse Width Modulation Output........................................................................................ 10
Detailed Description.................................................................................................................... 10
7.1
Incremental Outputs.............................................................................................................. 11
7.1.1
Incremental Power-up Lock Option .................................................................................. 11
7.2
Incremental Output Hysteresis............................................................................................... 12
7.3
Synchronous Serial Interface (SSI) ........................................................................................ 12
7.3.1
7.4
Data Contents ................................................................................................................ 13
Absolute Output Jitter and Hysteresis .................................................................................... 14
7.4.1
Adding a Digital Hysteresis ............................................................................................. 14
7.4.2
Implementing Digital Filtering .......................................................................................... 14
7.5
Z-axis Range Indication (“Red/Yellow/Green” Indicator) .......................................................... 14
8
Pulse Width Modulation (PWM) Output ........................................................................................ 15
9
3.3V / 5V Operation .................................................................................................................... 15
10
Magnet Specifications .............................................................................................................. 16
10.1
Magnetization .................................................................................................................... 16
10.2
Position of the Index Pulse ................................................................................................. 17
10.3
Mounting the Magnet ......................................................................................................... 17
11
10.3.1
Vertical Distance ......................................................................................................... 17
10.3.2
Alignment of Multi-pole Magnet and IC.......................................................................... 17
10.3.3
Lateral stroke of Multi-pole Strip Magnets ..................................................................... 17
Measurement Data Example ..................................................................................................... 19
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AS5311
Data Sheet
12
AS5311 Off-axis Rotary Applications ........................................................................................ 20
13
Package Drawings and Marking ................................................................................................ 21
14
Ordering Information ................................................................................................................ 22
15
Recommended PCB Footprint................................................................................................... 22
16
Revision History ...................................................................................................................... 23
17
Copyrights ............................................................................................................................... 23
18
Disclaimer ............................................................................................................................... 23
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AS5311
Data Sheet
5 Pinout
5.1 Pin Assignments
Figure 4: AS5311 Pin Configuration, TSSOP-20
1
20
NC
MagIncn
2
19
VDD5V
MagDecn
3
18
VDD3V3
A
4
17
NC
B
5
16
NC
NC
6
15
PWM
Index
7
14
CSn
VSS
8
13
CLK
Prog
9
12
DO
NC
10
11
NC
AS5311
NC
5.2 Pin Description
Pin 4(A), 5(B) and 7(Index) are the incremental outputs. The incremental output has a resolution of 10-bit per
pole pair, resulting in a step length of 1.95µm.
Note that Pin 14 (CSn) must be low to enable the incremental outputs.
Pins 12, 13 and 14 are used for serial data transfer. Chip Select (CSn; active low) initiates serial data transfer.
CLK is the clock input and DO is the data output. A logic high at CSn puts the data output pin (DO) to tri-state
and terminates serial data transfer. CSn must be low to enable the incremental outputs. See 7.1.1 for further
options.
Pin 8 is the supply ground pin. Pins 18 and 19 are the positive supply pins.
For 5V operation, connect the 5V supply to pin 19 and add a 2µ2…10µF buffer capacitor at pin 19.
For 3.3V operation, connect both pins 18 and 19 to the 3.3V supply.
Pin 9 is used for factory programming only. It should be connected to VSS.
Pins 2 and 3 are the magnetic field change indicators, MagINCn and MagDECn (magnetic field strength increase
or decrease through variation of the distance between the magnet and the device). These outputs can be used
to detect the valid magnetic field range.
External pull-up resistors are required at these pins. See 6.3.2 for maximum output currents on these pins. Since
they are open-drain outputs they can also be combined (wired-and).
Pin 15 (PWM) allows a single wire output of the 12-bit absolute position value within one pole pair (2.0mm). The
value is encoded into a pulse width modulated signal with 1µs pulse width per step (1µs to 4097µs over one pole
pair).
Pins 6, 10, 11, 16, 17 and 20 are for internal use and must not be connected.
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AS5311
Data Sheet
Table 1
Pin Description
Pin
Symbol
Type
Description
1
NC
-
2
MagINCn
DO_OD
Magnet Field Magnitude INCrease; active low, indicates a distance
reduction between the magnet and the device surface.
3
MagDECn
DO_OD
Magnet Field Magnitude DECrease; active low, indicates a distance
increase between the device and the magnet.
4
A
DO
Incremental output A
5
B
DO
Incremental output B
6
NC
-
Must be left unconnected
7
Index
DO
Incremental output Index.
Must be left unconnected
8
VSS
S
9
Prog
DI_PD
Negative Supply Voltage (GND)
10
NC
-
OTP Programming Input for factory programming. Connect to VSS
Must be left unconnected
11
NC
-
12
DO
DO_T
Data Output of Synchronous Serial Interface
13
CLK
DI, ST
Clock Input of Synchronous Serial Interface; Schmitt-Trigger input
14
CSn
DI_PU, ST
15
PWM
DO
16
NC
-
Must be left unconnected
17
NC
-
Must be left unconnected
18
VDD3V3
S
3V-Regulator output; internally regulated from VDD5V. Connect to
VDD5V for 3V supply voltage. Do not load externally.
19
VDD5V
S
Positive Supply Voltage, 3.0 to 5.5 V
20
NC
-
Must be left unconnected
DO_OD
DO
DI_PD
DI_PU
digital
digital
digital
digital
output open drain
output
input pull-down
input pull-up
Must be left unconnected
Chip Select, active low; Schmitt-Trigger input, internal pull-up resistor
(~50kΩ). Must be low to enable incremental outputs
Pulse Width Modulation of approx. 244Hz; 1µs/step
S
DI
DO_T
ST
supply pin
digital input
digital output /tri-state
Schmitt-Trigger input
6 Electrical Characteristics
6.1 Absolute Maximum Ratings
Stresses beyond those listed under “Absolute Maximum Ratings“ may cause permanent damage to the device.
These are stress ratings only. Functional operation of the device at these or any other conditions beyond those
indicated under “Operating Conditions” is not implied. Exposure to absolute maximum rating conditions for
extended periods may affect device reliability.
Table 2
Absolute Maximum Ratings
Parameter
Min
Max
Unit
DC supply voltage at pin VDD5V
-0.3
7
V
5
V
DC supply voltage at pin VDD3V3
Comments
Input pin voltage
-0.3
VDD5V +0.3
V
Except VDD3V3
Input current (latchup immunity)
-100
100
mA
Norm: JEDEC 78
±2
kV
Norm: MIL 883 E method 3015
125
°C
Min – 67°F ; Max +257°F
Electrostatic discharge
Storage temperature
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AS5311
Data Sheet
Parameter
Min
Max
Body temperature (Lead-free
package)
Humidity non-condensing
5
Unit
260
°C
85
%
Comments
t=20 to 40s, Norm: IPC/JEDEC J-Std-020C
Lead finish 100% Sn “matte tin”
6.2 Operating Conditions
Table 3
Operating Conditions
Parameter
Symbol
Min
Ambient temperature
Tamb
-40
Supply current
Isupp
Supply voltage at pin VDD5V
Typ
Max
Unit
125
°C
16
21
mA
Voltage regulator output
voltage at pin VDD3V3
VDD5V
4.5
5.0
5.5
V
VDD3V3
3.0
3.3
3.6
V
Supply voltage at pin VDD5V
VDD5V
3.0
3.3
3.6
V
Supply voltage at pin VDD3V3
VDD3V3
3.0
3.3
3.6
V
Note
-40°F…+257°F
5V Operation
3.3V Operation
(pin VDD5V and VDD3V3
connected)
6.3 DC Characteristics for Digital Inputs and Outputs
6.3.1
CMOS Schmitt-Trigger Inputs: CLK, CSn (CSn = internal Pull-up)
Operating conditions: Tamb = -40 to +125°C, VDD5V = 3.0-3.6V (3V operation) VDD5V = 4.5-5.5V (5V operation) unless
otherwise noted.
Parameter
Symbol
Min
High level input voltage
VIH
0.41 * VDD5V
Low level input voltage
VIL
Schmitt Trigger hysteresis
Pull-up low level input current
6.3.2
Unit
V
0.13 * VDD5V
VIon - VIoff
Input leakage current
Max
1
Note
Normal operation
V
V
ILEAK
-1
1
IiL
-30
-100
CLK only
µA
CSn only, VDD5V: 5.0V
CMOS Output Open Drain: MagINCn, MagDECn
Operating conditions: Tamb = -40 to +125°C, VDD5V = 3.0-3.6V (3V operation) VDD5V = 4.5-5.5V (5V operation) unless
otherwise noted.
Parameter
Low level output voltage
Output current
Open drain leakage current
6.3.3
Symbol
Min
VOL
Max
Unit
VSS+0.4
V
4
IO
mA
2
IOZ
1
Note
VDD5V: 4.5V
VDD5V: 3V
µA
CMOS Output: PWM
Operating conditions: Tamb = -40 to +125°C, VDD5V = 3.0-3.6V (3V operation) VDD5V = 4.5-5.5V (5V operation) unless
otherwise noted.
Parameter
Symbol
Min
High level output voltage
VOH
VDD5V-0.5
Low level output voltage
VOL
Output current
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Max
Unit
Note
V
VSS+0.4
V
4
mA
VDD5V: 4.5V
2
mA
VDD5V: 3V
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AS5311
Data Sheet
6.3.4
Tristate CMOS Output: DO
Operating conditions: Tamb = -40 to +125°C, VDD5V = 3.0-3.6V (3V operation) VDD5V = 4.5-5.5V (5V operation) unless
otherwise noted.
Parameter
Symbol
Min
High level output voltage
VOH
VDD5V –0.5
Low level output voltage
VOL
VSS+0.4
V
IO
4
mA
VDD5V: 4.5V
2
mA
VDD5V: 3V
Output current
Max
Unit
Note
V
6.4 Magnetic Input Specification
Operating conditions: Tamb = -40 to +125°C, VDD5V = 3.0-3.6V (3V operation) VDD5V = 4.5 - 5.5V (5V operation) unless
otherwise noted.
Two-pole cylindrical diametrically magnetised source:
Parameter
Symbol
Min
Typ
Max
Unit
Pole length
Lp
1
mm
Pole pair length
tmag
2
mm
Magnetic input field
amplitude
Bpk
Magnetic offset
Boff
Magnetic field
temperature drift
10
Btc
Magnetic input field
variation
Note
Recommended magnet: plastic or rubber
bonded ferrite or NdFeB
Required vertical component of the magnetic
field strength on the die’s surface
40
mT
±5
mT
Constant magnetic stray field
0.2
%/K
Recommended magnet: plastic or rubber
bonded ferrite or NdFeB
±2
%
650
mm/
sec
Incremental output: 1024 steps / polepair
including interpolation 1)
Including offset gradient
Linear travelling speed
Vabs
Displacement
Disp
0.5
mm
Max. shift between defined Hall sensor
center and magnet centerline (see Figure
17); depends on magnet geometries
Vertical gap
ZDist
0.3
mm
Package to magnet surface;
depends on magnet strength
-0.19
Recommended magnet
material and
temperature drift
Plastic or rubber bonded Ferrite
%/K
-0.12
Plastic or rubber bonded Neodymium
(NdFeB)
1)
Note : There is no upper speed limit for the absolute outputs. With increasing speed, the distance between two
samples increases. The travelling distance between two subsequent samples can be calculated as:
sampling _ dist =
v
fs
where: sampling_distance = travelling distance between samples in mm
v = travelling speed in mm/sec
fs = sampling rate in Hz
(see 6.5 below)
6.5 Electrical System Specifications
Operating conditions: Tamb = -40 to +125°C, VDD5V = 3.0~3.6V (3V operation) VDD5V = 4.5~5.5V (5V operation) unless
otherwise noted.
Parameter
Symbol
Resolution, absolute outputs
RESabs
12
bit /
polepair
0.488 um/step (12bit / 2mm pole
pair)
Resolution, incremental
outputs
RESinc
10
bit /
polepair
1.95 um/step (10bit / 2mm pole
pair)
Integral non-linearity
(optimum)
INLopt
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Min
Typ
Max
± 5.6
Revision 1.01
Unit
μm
Note
Maximum error with respect to the
best line fit. Ideal magnet
Tamb =25 °C.
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AS5311
Data Sheet
Parameter
Integral non-linearity (over
temperature)
Differential non-linearity
Symbol
Max
Unit
Note
INLtemp
± 10
μm
Maximum error with respect to the
best line fit. Ideal magnet
Tamb = -30 to +70 °C.
DNL
±0.97
μm
10bit, no missing codes
0.6
μm
RMS
Transition noise
Min
Typ
TN
Power-on reset thresholds
On voltage; 300mV typ.
hysteresis
Off voltage; 300mV typ.
hysteresis
Von
1.37
DC supply voltage 3.3V (VDD3V3)
2.9
2.2
1 sigma
V
1.08
Voff
DC supply voltage 3.3V (VDD3V3)
2.6
1.9
Power-up time
tPwrUp
20
ms
Until status bit OCF = 1
System propagation delay
absolute output :
tdelay
96
µs
Delay of ADC, DSP and absolute
interface
System propagation delay
incremental output
tdelay
384
µs
Including interpolation delay at
high speeds
Internal sampling rate for
absolute output
fS
Hysteresis, incremental
outputs
Read-out frequency
9.90
10.42
10.94
9.38
10.42
11.46
Hyst
kHz
2
LSB
CLK
1
MHz
Tamb = 25°C
Tamb = -40 to +125°C,
No Hysteresis at absolute serial
outputs
Max. clock frequency to read out
serial data
Integral Non-Linearity (INL) is the maximum deviation between actual position and indicated position.
Differential Non-Linearity (DNL) is the maximum deviation of the step length from one position to the next.
Transition Noise (TN) is the repeatability of an indicated position.
6.6 Timing Characteristics
6.6.1
Synchronous Serial Interface (SSI)
Operating conditions: Tamb = -40 to +125°C, VDD5V = 3.0~3.6V (3V operation) VDD5V = 4.5~5.5V (5V operation) unless
otherwise noted.
Parameter
Data output activated
(logic high)
Symbol
Min
t DO active
Typ
Max
Unit
Note
100
ns
Time between falling edge of CSn and
data output activated
First data shifted to
output register
tCLK FE
500
ns
Time between falling edge of CSn and
first falling edge of CLK
Start of data output
T CLK / 2
500
ns
Rising edge of CLK shifts out one bit at
a time
Data output valid
t DO valid
413
ns
Time between rising edge of CLK and
data output valid
Data output tristate
t DO
tristate
100
ns
After the last bit DO changes back to
“tristate”
Pulse width of CSn
t CSn
500
ns
CSn = high; To initiate read-out of next
angular position
Read-out frequency
fCLK
>0
MHz
Clock frequency to read out serial data
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AS5311
Data Sheet
6.6.2
Pulse Width Modulation Output
Operating conditions: Tamb = -40 to +125°C, VDD5V = 3.0~3.6V (3V operation) VDD5V = 4.5~5.5V (5V operation) unless
otherwise noted.
Parameter
PWM frequency
Symbol
f PWM
Min
Typ
Max
232
244
256
Unit
Note
Hz
Signal period = 4098µs ±5% at Tamb =
25°C
= 4098µs ±10% at Tamb = -40 to +125°C
220
244
268
Minimum pulse width
PW MIN
0.9
1
1.1
µs
Position 0d =0µm
Maximum pulse width
PW MAX
3892
4097
4301
µs
Position 4095d = 1999.5µm
7 Detailed Description
The different types of outputs relative to the magnet position are outlined in Figure 5 below.
The absolute serial output counts from 0….4095 within one pole pair and repeats with each subsequent pole
pair.
Likewise, the PWM output starts with a pulse width of 1µs, increases the pulse width with every step of 0.488µm
and reaches a maximum pulse width of 4097µs at the end of each pole pair.
An index pulse is generated once for every pole pair.
256 incremental pulses are generated at each output A and B for every pole pair. The outputs A and B are
phase shifted by 90 electrical degrees, which results in 1024 edges per pole pair. As the incremental outputs are
also repeated with every pole pair, a constant train of pulses is generated as the magnet moves over the chip.
Figure 5: AS5311 Outputs Relative to Magnet Position
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AS5311
Data Sheet
7.1 Incremental Outputs
Figure 6 shows the two-channel quadrature output of the AS5311. Output A leads output B when the magnet is
moving from right to left and output B leads output A when the magnet is moving from left to right
(see Figure 14).
Figure 6: Incremental Outputs
M echanical
Z ero P osition
Increm en tal o utputs
M ovem ent Direction
Change
M echanical
Zero Position
A
B
Index= 0
1 LSB
In d e x
Movem ent right to left
CS n
t
7.1.1
H y st =
2 LSB
Movement left to right
In cre m e n tal o u tp u ts va lid
Incremental Power-up Lock Option
After power-up, the incremental outputs can optionally be locked or unlocked, depending on the status of the
CSn pin:
CSn = low at power-up:
CSn has an internal pull-up resistor and must be externally pulled low (Rext ≤ 5kΩ). If Csn is low at
power-up, the incremental outputs A, B and Index will be high until the internal offset compensation is
finished.
This unique state may be used as an indicator for the external controller to shorten the waiting time at
power-up. Instead of waiting for the specified maximum power up-time (see 6.5), the controller can start
requesting data from the AS5311 as soon as the state (A=B=Index = high) is cleared.
CSn = high or open at power-up:
In this mode, the incremental outputs (A, B, Index) will remain at logic high state, until CSn goes low or
a low pulse is applied at CSn. This mode allows intentional disabling of the incremental outputs until for
example the system microcontroller is ready to receive data.
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AS5311
Data Sheet
7.2 Incremental Output Hysteresis
Figure 7: Hysteresis Illustration
Incremental
Output
Indication
X +4
Hysteresis:
2 steps
X +3
X +2
X +1
X
X
Magnet Position
X +1 X +2 X +3 X +4 X +5
Movement left -> right
Movement right -> left
To avoid flickering incremental outputs at a stationary magnet position, a hysteresis is introduced.
In case of a movement direction change, the incremental outputs have a hysteresis of 2 LSB. For constant
movement directions, every magnet position change is indicated at the incremental outputs (see Figure 6). If for
example the magnet moves from position „x+3“ to „x+4“, the incremental output would also indicate this position
accordingly.
A change of the magnet’s movement direction back to position „x+3“ means, that the incremental output still
remains unchanged for the duration of 2 LSB, until position „x+2“ is reached. Following this movement, the
incremental outputs will again be updated with every change of the magnet position.
7.3 Synchronous Serial Interface (SSI)
The Serial interface allows data transmission of the 12-bit absolute linear position information (within one pole
pair = 2.0mm). Data bits D11:D0 represent the position information with a resolution of 488nm (2000µm / 4096)
per step.
CLK must be high at the falling edge of CSn.
Figure 8: Synchronous Serial Interface with Absolute Angular Position Data
tCLK FE
CSn
TCLK/2
tCLK FE
tCSn
1
CLK
DO
8
D11
tDO active
D10
D9
D8
D7
D6
D5
D4
18
D3
D2
D1
D0
OCF
COF
LIN
Mag
INC
tDO valid
Angular Position Data
Status Bits
Mag
DEC
1
Even
PAR
D11
tDO Tristate
If CLK is low at the falling edge of CSn, the first 12 bits represent the magnitude information, which is
proportional to the magnetic field strength. This information can be used to detect the presence and proper
distance of the magnetic strip by comparing it to a known good value (depends on the magnet material and
distance).
The automatic gain control (AGC) maintains a constant MAGnitude value of 3F hex (=”green” range). If the MAG
value is <>3F hex, the AGC is out of the regulating range (“yellow” or “red” range). See Table 5 for more details.
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AS5311
Data Sheet
A value of zero or close to zero indicates a missing magnet.
Figure 9: Synchronous Serial Interface with Magnetic Field Strength Data
tCLK FE
CSn
TCLK/2
tCSn
1
CLK
DO
8
0
0
0
0
0
M6
M5
M4
18
M3
M2
M1
M0
OCF
COF
LIN
Mag
INC
tDO valid
tDO active
Magnetic field strength data
Status Bits
Mag
DEC
1
Even
PAR
D11
tDO Tristate
If CSn changes to logic low, Data Out (DO) will change from high impedance (tri-state) to logic high and the
read-out will be initiated.
ƒ
After a minimum time t CLK FE, data is latched into the output shift register with the first falling edge of CLK.
ƒ
Each subsequent rising CLK edge shifts out one bit of data.
ƒ
The serial word contains 18 bits, if CLK is high at the falling edge of CSn (Figure 8), the first 12 bits are the
absolute distance information D[11:0], the subsequent 6 bits contain system information, about the validity
of data such as OCF, COF, LIN, Parity and Magnetic Field status (increase/decrease).
ƒ
If CLK is low at the falling edge of CSn (Figure 9), the first 12 bits contain the magnitude information
(range = 00…7F hex) and the subsequent bits contain the status bits (see above)
ƒ
A subsequent measurement is initiated by a “high” pulse at CSn with a minimum duration of tCSn.
7.3.1
Data Contents
D11:D0 absolute linear position data (MSB is clocked out first)
M11:M0 magnitude / magnetic field strength information (MSB is clocked out first)
OCF (Offset Compensation Finished), logic high indicates the finished Offset Compensation Algorithm
COF (Cordic Overflow), logic high indicates an out of range error in the CORDIC part. When this bit is set,
the data at D11:D0 (likewise M11:M0) is invalid.
This alarm may be resolved by bringing the magnet within the X-Y-Z tolerance limits.
LIN (Linearity Alarm), logic high indicates that the input field generates a critical output linearity.
When this bit is set, the data at D11:D0 may still be used, but can contain invalid data. This warning can be
resolved by increasing the magnetic field strength.
Even Parity bit for transmission error detection of bits 1…17 (D11…D0, OCF, COF, LIN, MagINC, MagDEC)
Data D11:D0 is valid, when the status bits have the following configurations:
Table 4: Status Bit Outputs
OCF
1
COF
0
LIN
0
Mag
INC
Mag
DEC
0
0
0
1
1
0
1*)
1*)
Parity
even checksum of bits 1:15
*) MagInc=MagDec=1 is only recommended in YELLOW mode (see Table 5)
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AS5311
Data Sheet
7.4 Absolute Output Jitter and Hysteresis
Note that there is no hysteresis or additional filtering at the absolute output. This allows a determination of the
magnet’s absolute position within one pole pair down to submicron range.
Due to the intentionally omitted hysteresis and due to noise (e.g. from weak magnetic fields), the absolute output
may jitter when the magnet is stationary over the chip.
In order to get a stable 12-bit absolute reading, two common methods may be implemented to reduce the jitter.
7.4.1
Adding a Digital Hysteresis
The hysteresis feature of the incremental outputs is described in 7.2. An equivalent function can be implemented
in the software of the external microcontroller. The hysteresis should be larger than the peak-to-peak noise
(=jitter) of the absolute output in order to mask it and create a stable output reading.
Remark: the 2-bit hysteresis on the incremental output (=3.9µm) is equivalent to a hysteresis of 8LSB on the
absolute output.
7.4.2
Implementing Digital Filtering
Another useful alternative or additional method to reduce jitter is digital filtering. This can be accomplished
simply by averaging, for example a moving average calculation in the external microcontroller. Averaging 4
readings results in 6dB (=50%) noise and jitter reduction. An average of 16 readings reduces the jitter by a
factor of 4.
Averaging causes additional latency of the processed data. Therefore it may be useful to adjust the depth of
averaging depending on speed of travel. For example using a larger depth when the magnet is stationary and
reducing the depth when the magnet is in motion.
7.5 Z-axis Range Indication (“Red/Yellow/Green” Indicator)
The AS5311 provides several options of detecting the magnet distance by indicating the strength of the
magnetic field. Signal indicators MagINCn and MagDECn are available both as hardware pins (pins 1 and 2) and
as status bits in the serial data stream (see Figure 8). Additionally the LIN status bit indicates the nonrecommended “red” range. The MAGnitude register provides additional information about the strength of the
magnetic field (see Figure 9).
The digital status bits MagINC, MagDec, LIN and the hardware pins MagINCn, MagDECn have the following
function:
Table 5: Magnetic Field Strength Red-Yellow-Green Indicators
Status Bits
MAG
Hardware Pins
Mag
INC
Mag
DEC
LIN
M11..
M0
Mag
INCn
Mag
DECn
0
0
0
3F hex
Off
Off
No distance change
Magnetic input field OK ( GREEN range, ~10…40mT peak
amplitude)
0
1
0
3F hex
Off
Off
Distance increase; this state is a dynamic state and only
active while the magnet is moving away from the chip.
Magnitude register may change but regulates back to 3F hex.
1
0
0
3F hex
Off
Off
Distance decrease; this state is a dynamic state and only
active while the magnet is moving towards the chip.
Magnitude register may change but regulates back to 3F hex.
1
1
0
20 hex5F hex
On
Off
YELLOW range: magnetic field is ~3.4….54.5mT.
The AS5311 may still be operated in this range, but with
slightly reduced accuracy.
1
<20 hex
>5F hex
1
1
All other combinations
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On
On
n/a
n/a
Description
RED range: magnetic field is <3.4mT (MAG <20) or >54.5mT
(MAG >5F).
It is still possible to operate the AS5311 in the red range, but
not recommended.
Not available
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AS5311
Data Sheet
8 Pulse Width Modulation (PWM) Output
The AS5311 provides a pulse width modulated output (PWM), whose duty cycle is proportional to the relative
linear position of the magnet within one pole pair (2.0mm). This cycle repeats after every subsequent pole pair:
Position =
t on ⋅ 4098
(ton + toff ) − 1
for digital position = 0 – 4094
Exception:
A linear position of 1999.5µm = digital position 4095
will generate a pulse width of ton = 4097µs and a pause toff = 1µs
The PWM frequency is internally trimmed to an accuracy of ±5% (±10% over full temperature range). This
tolerance can be cancelled by measuring the complete duty cycle as shown above.
Figure 10: PWM Output Signal
Position
PW MIN
0µm
(Pos 0)
1µs
4098µs
PW MA X
1999.5µm
(Pos 4095)
4097µs
1/fPWM
9 3.3V / 5V Operation
The AS5311 operates either at 3.3V ±10% or at 5V ±10%. This is made possible by an internal 3.3V LowDropout (LDO) Voltage regulator. The internal supply voltage is always taken from the output of the LDO,
meaning that the internal blocks are always operating at 3.3V.
For 3.3V operation, the LDO must be bypassed by connecting VDD3V3 with VDD5V (see Figure 11).
For 5V operation, the 5V supply is connected to pin VDD5V, while VDD3V3 (LDO output) must be buffered by a
2.2...10µF capacitor, which is supposed to be placed close to the supply pin.
The VDD3V3 output is intended for internal use only It must not be loaded with an external load.
The output voltage of the digital interface I/O’s corresponds to the voltage at pin VDD5V, as the I/O buffers are
supplied from this pin.
A buffer capacitor of 100nF is recommended in both cases close to pin VDD5V. Note that pin VDD3V3 must
always be buffered by a capacitor. It must not be left floating, as this may cause an instable internal 3.3V supply
voltage which may lead to larger than normal jitter of the measured angle.
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AS5311
Data Sheet
Figure 11: Connections for 5V and 3.3V Supply Voltages
5V Operation
3.3V Operation
2.2...10µF
VDD3V3
VDD3V3
100n
100n
VDD5V
LDO
Internal
VDD
Prog
LDO
Internal
VDD
PWM
I
N
T
E
R
F
A
C
E
4.5 - 5.5V
VDD5V
PWM
DO
3.0 - 3.6V
CLK
CSn
A
B
Prog
Index
VSS
I
N
T
E
R
F
A
C
E
DO
CLK
CSn
A
B
Index
VSS
AS5311
AS5311
10 Magnet Specifications
10.1 Magnetization
The AS5311 accepts magnetic multi-pole strip or ring magnets with a pole length of 1.0mm. Recommended
magnet materials include plastic or rubber bonded ferrite or Neodymium magnets.
It is not recommended to use the AS5311 with other pole lengths as this will create additional nonlinearities.
Figure 12: Additional Error from Pole Length Mismatch
AS5311 Systematic Linearity Error Caused by Pole
Length Deviation
70.00
60.00
Error 50.00
[µm] 40.00
Error [µm]
30.00
20.00
10.00
0.00
750 800 850 900 950 1000 1050 1100 1150 1200 1250
Pole Length [µm]
Figure 12 shows the error caused by a mismatch of pole length. Note that this error is an additional error on top
of the chip-internal INL and DNL errors (see 6.5). For example, when using a multi-pole magnet with 1.2mm pole
length instead of 1.0mm, the AS5311 will provide 1024 incremental steps or 4096 absolute positions over
2.4mm, but with an additional linearity error of up to 50µm.
The curvature of ring magnets may cause linearity errors as well due to the fact that the Hall array on the chip is
a straight line while the poles on the multi-pole ring are curved. These errors decrease with increasing ring
diameter. It is therefore recommended to keep the ring diameter measured at the location of the Hall array at
20mm or higher.
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Revision 1.01
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AS5311
Data Sheet
10.2 Position of the Index Pulse
An index pulse is generated when the North and South poles are placed over the Hall array as shown in
Figure 14.
The incremental output count increases when the magnet is moving to the left, facing the chip with pin#1 at the
lower left corner (see Figure 14, top drawing). At the same time, the absolute position value increases.
Likewise, the position value decreases when the magnet is moved in the opposite direction.
10.3 Mounting the Magnet
10.3.1 Vertical Distance
As a rule of thumb, the gap between chip and magnet should be ½ of the pole length, that is Z=0.5mm for the
1.0mm pole length of the AS5311 magnets. However, the gap also depends on the strength of the magnet.
Typical gaps for AS5311 magnets range from 0.3 to 0.6mm (see 6.4).
The AS5311 automatically adjusts for fluctuating magnet strength by using an automatic gain control (AGC). The
vertical distance should be set such that the AS5311 is in the “green” range. See 7.5 for more details.
10.3.2 Alignment of Multi-pole Magnet and IC
When aligning the magnet strip or ring to the AS5311, the centerline of the magnet strip should be placed
exactly over the Hall array. A lateral displacement in Y-direction (across the width of the magnet) is acceptable
as long as it is within the active area of the magnet. See Figure 14 for the position of the Hall array relative to
Pin #1.
Note: the active area in width is the area in which the magnetic field strength across the width of the magnet is
constant with reference to the centerline of the magnet (see Figure 13 ).
10.3.3 Lateral stroke of Multi-pole Strip Magnets
The lateral movement range (stroke) is limited by the area at which all Hall sensors of the IC are covered by the
magnet in either direction. The Hall array on the AS5311 has a length of 2.0mm, hence the total stroke is
maximum lateral Stroke = Length of active area – length of Hall array
Note: active area in length is defined as the area containing poles with the specified 1.0mm pole length. Shorter
poles at either edge of the magnet must be excluded from the active area (see Figure 13).
Bpk Bpk
Figure 13: Active Area of Strip Magnet
Active Area
Active area (length)
Active area
(width)
B
N
S
2mm
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N
S
N
S
N
S
N
S
recommended
scanning path
strip length
Revision 1.01
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AS5311
Data Sheet
Figure 14: Alignment of Magnet Strip with AS5311 Sensor IC
position value
increases
leftmost magnet position
Die C/L
S
N
S
N
S
N
S
N
S
3.0475±0.235
N
AS5311
Package
Outline
1.00
position value
decreases
rightmost magnet position
S
2.576±0.235
3.200±0.235
Die C/L
N
S
N
S
N
S
N
S
N
1.00
3.0475±0.235
vertical airgap
magnet
strip
carrier
see text
1.00 ± 0.1
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Revision 1.01
Note: all dimensions are in mm
18 - 23
AS5311
Data Sheet
11 Measurement Data Example
Figure 15 shows typical test results of the accuracy obtained by a commercially available multi-pole magnetic
strip.
The graph shows the accuracy over a stroke of 8mm at two different vertical gaps, 0.2mm and 0.4mm. As
displayed, the accuracy is virtually identical (about +/- 10µm) for both airgaps due to the automatic gain control
of the AS5311 which compensates for airgap changes.
The accuracy depends greatly on the length and strength of each pole and hence from the precision of the tool
used for magnetization as well as the homogeneity of the magnet material. As the error curve in the example
below does not show a repetitive pattern for each pole pair (each 2.0mm), this is most likely an indication that
the pole lengths of this particular sample do not exactly match. While the first pole pair (0...2mm) shows the
greatest nonlinearities, the second pole (2…4mm) is very precise, etc…
Error [µm]
Figure 15: Sample Test Results of INL at Different Airgaps
25
20
15
10
5
0
-5
-10
-15
-20
-25
INL MS10-10
z= 200µ
z= 400µ
0
1000
2000
3000
4000
5000
6000
7000
8000
X [µm]
Note: the magnet sample used in Figure 15 is a 10-pole plastic bonded ferrite magnet as shown in Figure 13.
The corresponding magnet datasheet (MS10-10) is available for download from the austriamicrosystems
website, magnet samples can be ordered from the austriamicrosystems online web shop.
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AS5311
Data Sheet
12 AS5311 Off-axis Rotary Applications
The AS5311 can also be used as an off-axis rotary encoder, as shown in Figure 3. In such applications, the
multi-pole magnetic strip is replaced by a multi-pole magnetic ring. The ring can have radial or axial
magnetization.
Figure 16: Angular Resolution and Maximum Speed versus Ring Diameter
In off-axis rotary applications, very high
angular resolutions are possible with the
AS5311.
The number of steps per revolution
increases linearly with ring diameter.
Due to the increasing number of pulses per
revolution, the maximum speed decreases
with increasing ring diameter.
AS5311 off-axis rotary resolution & speed
700
160000
resolution
speed rpm
140000
600
500
100000
400
80000
300
60000
max. speed [rpm]
resolution [steps / rev]
120000
Example:
a magnetic ring with 41.7mm diameter has
a resolution of 65536 steps per revolution
(16-bit) and a maximum speed of 305 rpm
200
40000
100
20000
0
0
20
40
60
80
100
ring diameter [mm]
Res
[bit]
Steps /
Rev.
Ring
Diameter
[mm]
Max
Speed
[rpm]
15
32768
20.9
609
16
65536
41.7
305
17
131072
83.4
152
The number of incremental steps per revolution can be calculated as:
incremental _ steps = 1024 * nbr _ polepairs
incremental _ steps =
1024 * d * π
2
Note that the circumference (d*π) must be a multiple of one polepair = 2mm, hence the diameter of the magnet
ring may need to be adjusted accordingly:
d=
nbr _ polepairs * 2mm
π
The maximum rotational speed can be calculated as:
max_ rot _ speed =
max_ lin _ speed * 60 39000
=
d *π
d *π
where
nbr_polepairs
d
= the number of pole pairs at the magnet ring
= diameter of the ring in mm; the diameter is taken at the locus of the Hall elements
underneath the magnet
max_rot_speed = maximum rotational speed in revolutions per minute rpm :
max_lin_speed = maximum linear speed in mm/sec (=650 mm/s for AS5311)
Note:
further examples are shown in the “Magnet Selection Guide”, available for download from the
austriamicrosystems website
http://www.austriamicrosystems.com/eng/Products/Magnetic-Encoders/Linear-Encoders
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Revision 1.01
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AS5311
Data Sheet
13 Package Drawings and Marking
20 Lead Thin Shrink Small Outline Package – TSSOP20
Figure 17: AS5311 Package Dimensions and Hall Array Location
0.2299±0.100
Die C/L
2.576±0.235
3.200±0.235
0.2341±0.100
Package
Outline
0.7701±0.150
3.0475±0.235
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Revision 1.01
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AS5311
Data Sheet
Dimensions
Symbol
Marking: AYWWIZZ
mm
Min
Typ
Max
Min
Typ
Max
A
-
-
1.10
-
-
0.043
A1
0.05
-
0.15
0.002
-
0.006
A2
0.85
0.90
0.95
0.033
0.035
0.037
b
0.19
-
0.30
0.007
-
0.012
0.004
-
0.008
c
0.09
-
0.20
D
6.40
6.50
6.60
E
6.20
6.40
6.60
0.244
0.252
0.260
E1
4.30
4.40
4.50
0.169
0.173
0.177
K
0°
0.65
-
8°
0°
-
8°
L
0.50
0.60
0.75
0.019
0.024
0.030
e
A: Pb-Free Identifier
Y: Last Digit of Manufacturing Year
WW: Manufacturing Week
I: Plant Identifier
ZZ: Traceability Code
inch
JEDEC Package Outline Standard:
MO – 153
Thermal Resistance Rth(j-a):
89 K/W in still air, soldered on PCB.
.0256
IC's marked with a white dot or the letters "ES"
denote Engineering Samples
14 Ordering Information
Delivery:
Tape and Reel (1 reel = 2000 devices)
Tubes (1 box = 100 tubes à 77 devices)
Order # AS5311ASSU
Order # AS5311ASST
for delivery in tubes
for delivery in tape and reel
15 Recommended PCB Footprint
Recommended Footprint Data
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A
mm
7.00
inch
0.276
B
5.00
0.197
C
0.38
0.015
D
0.65
0.026
E
6.23
0.245
Revision 1.01
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AS5311
Data Sheet
16 Revision History
Revision
Date
Owner
1.01
26-Jun-09
jja, jlu
Description
Recommended footprint data updated
17 Copyrights
Copyright © 2009, austriamicrosystems AG, Schloss Premstaetten, 8141 Unterpremstaetten, Austria – Europe.
Trademarks Registered ®. All rights reserved. The material herein may not be reproduced, adapted, merged,
translated, stored, or used without the prior written consent of the copyright owner.
All products and companies mentioned are trademarks or registered trademarks of their respective companies.
18 Disclaimer
Devices sold by austriamicrosystems AG are covered by the warranty and patent indemnification provisions
appearing in its Term of Sale. austriamicrosystems AG makes no warranty, express, statutory, implied, or by
description regarding the information set forth herein or regarding the freedom of the described devices from
patent infringement. austriamicrosystems AG reserves the right to change specifications and prices at any time
and without notice. Therefore, prior to designing this product into a system, it is necessary to check with
austriamicrosystems AG for current information. This product is intended for use in normal commercial
applications. Applications requiring extended temperature range, unusual environmental requirements, or high
reliability applications, such as military, medical life-support or lifesustaining equipment are specifically not
recommended without additional processing by austriamicrosystems AG for each application.
The information furnished here by austriamicrosystems AG is believed to be correct and accurate. However,
austriamicrosystems AG shall not be liable to recipient or any third party for any damages, including but not
limited to personal injury, property damage, loss of profits, loss of use, interruption of business or indirect,
special, incidental or consequential damages, of any kind, in connection with or arising out of the furnishing,
performance or use of the technical data herein. No obligation or liability to recipient or any third party shall arise
or flow out of austriamicrosystems AG rendering of technical or other services.
Contact Information
Headquarters
austriamicrosystems AG
A-8141 Schloss Premstaetten, Austria
Tel: +43 (0) 3136 500 0
Fax: +43 (0) 3136 525 01
For Sales Offices, Distributors and Representatives, please visit:
http://www.austriamicrosystems.com/contact
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