AS5311
High Resolution Magnetic Linear Encoder
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Datasheet
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
1.95µm 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).
Figure 1. AS5311 Block Diagram
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
Two 12-bit digital absolute outputs:
- Serial interface and
- Pulse width modulated (PWM) output
Incremental output with Index
“Red-Yellow-Green” indicators monitor magnet placement over
the chip
3 Applications
Micro-Actuator feedback
Servo drive feedback
Robotics
Replacement of optical encoders
DSP
Linear Hall
Array
&
Frontend
Amplifier OTP
Register
Programming
Parameters
Absolute
Interface
(SSI)
Incremental
Interface
Sin
Cos
Ang
Mag
MagINCn
MagDECn
DO
PWM
CLK
A
B
Index
Prog
CSn
PWM
Interface
VDD5V
VDD3V3
LDO 3.3V
AS5311
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AS5311
Datasheet - Contents
Contents
1 General Description .................................................................................................................................................................. 1
2 Key Features............................................................................................................................................................................. 1
3 Applications............................................................................................................................................................................... 1
4 Pin Assignments ....................................................................................................................................................................... 3
4.1 Pin Descriptions.................................................................................................................................................................................... 3
5 Absolute Maximum Ratings ...................................................................................................................................................... 5
6 Electrical Characteristics........................................................................................................................................................... 6
6.1 Operating Conditions............................................................................................................................................................................ 6
6.2 DC Characteristics for Digital Inputs and Outputs ................................................................................................................................ 6
6.2.1 CMOS Schmitt-Trigger Inputs: CLK, CSn (CSn = internal Pull-up) ............................................................................................. 6
6.2.2 CMOS Output Open Drain: MagINCn, MagDECn ....................................................................................................................... 6
6.2.3 CMOS Output: PWM ................................................................................................................................................................... 6
6.2.4 Tristate CMOS Output: DO.......................................................................................................................................................... 7
6.3 Magnetic Input Specification................................................................................................................................................................. 7
6.4 Electrical System Specifications........................................................................................................................................................... 8
6.5 Timing Characteristics .......................................................................................................................................................................... 9
6.5.1 Pulse Width Modulation Output ................................................................................................................................................... 9
7 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
7.4 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
7.6 Pulse Width Modulation (PWM) Output.............................................................................................................................................. 15
7.7 3.3V / 5V Operation............................................................................................................................................................................ 16
8 Application Information ........................................................................................................................................................... 17
8.1 Magnetization ..................................................................................................................................................................................... 18
8.2 Position of the Index Pulse................................................................................................................................................................. 18
8.3 Mounting the Magnet.......................................................................................................................................................................... 19
8.3.1 Vertical Distance........................................................................................................................................................................ 19
8.3.2 Alignment of Multi-pole Magnet and IC...................................................................................................................................... 19
8.3.3 Lateral Stroke of Multi-pole Strip Magnets................................................................................................................................. 19
8.4 Measurement Data Example .............................................................................................................................................................. 21
8.5 AS5311 Off-axis Rotary Applications.................................................................................................................................................. 22
9 Package Drawings and Markings ........................................................................................................................................... 24
9.1 Recommended PCB Footprint............................................................................................................................................................ 25
10 Ordering Information............................................................................................................................................................. 27
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AS5311
Datasheet - Pin Assignments
4 Pin Assignments
Figure 2. Pin Assignments (Top View)
4.1 Pin Descriptions
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: 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 Section 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 2µF…10µF buffer capacitor at pin 18.
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 Section 6.2.2 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 1, 6, 10, 11, 16, 17 and 20 are for internal use and must not be connected.
2
3
4
5
6
7
813
14
15
16
17
18
19
201
NC
MagIncn
MagDecn
A
B
NC
Index
VSS CLK
CSn
PWM
NC
NC
VDD3V3
VDD5V
912 DO
Prog
10 11 NCNC
NC
AS5311
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AS5311
Datasheet - Pin Assignments
Table 1. Pin Descriptions
Pin Number Pin Name Pin Type Description
1NC -
Must be left unconnected
2 MagINCn
Digital output open
drain
Magnet Field Magnitude INCrease; active low, indicates a distance reduction
between the magnet and the device surface.
3 MagDECn Magnet Field Magnitude DECrease; active low, indicates a distance increase
between the device and the magnet.
4A
Digital output
Incremental output A
5B Incremental output B
6NC -
Must be left unconnected
7 Index Digital output Incremental output Index
8 VSS Supply pin Negative Supply Voltage (GND)
9 Prog Digital input pull-down OTP Programming Input for factory programming. Connect to VSS.
10 NC - Must be left unconnected
11 NC - Must be left unconnected
12 DO Digital output /tri-state Data Output of Synchronous Serial Interface
13 CLK Digital input,
Schmitt-Trigger input Clock Input of Synchronous Serial Interface; Schmitt-Trigger input
14 CSn Digital input pull-up,
Schmitt-Trigger input
Chip Select, active low; Schmitt-Trigger input, internal pull-up resistor (~50kW).
Must be low to enable incremental outputs
15 PWM Digital output Pulse Width Modulation of approx. 244Hz; 1µs/step
16 NC - Must be left unconnected
17 NC - Must be left unconnected
18 VDD3V3 Supply pin
3V-Regulator output; internally regulated from VDD5V.
Connect to VDD5V for 3V supply voltage. Do not load externally.
19 VDD5V Positive Supply Voltage, 3.0 to 5.5 V
20 NC - Must be left unconnected
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AS5311
Datasheet - Absolute Maximum Ratings
5 Absolute Maximum Ratings
Stresses beyond those listed in Table 2 may cause permanent damage to the device. These are stress ratings only, and functional operation of
the device at these or any other conditions beyond those indicated in Electrical System Specifications on page 8 is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
Table 2. Absolute Maximum Ratings
Parameter Min Max Units Comments
DC supply voltage at pin VDD5V -0.3 7 V
DC supply voltage at pin VDD3V3 5 V
Input pin voltage -0.3 VDD5V
+0.3 VExcept VDD3V3
Input current (latchup immunity) -100 100 mA Norm: JEDEC 78
Electrostatic discharge ± 2 kV Norm: MIL 883 E method 3015
Storage temperature -55 125 °C Min – 67°F; Max +257°F
Body temperature (Lead-free package) 260 °C
t=20 to 40s,
The reflow peak soldering temperature (body
temperature) specified is in accordance with IPC/
JEDEC J-STD-020C “Moisture/Reflow Sensitivity
Classification for Non-Hermetic Solid State Surface
Mount Devices”.
The lead finish for Pb-free leaded packages is matte tin
(100% Sn).
Humidity non-condensing 5 85 %
Moisture Sensitive Level (MSL) 3 Represents a maximum floor time of 168h
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AS5311
Datasheet - Electrical Characteristics
6 Electrical Characteristics
TAMB = -40 to +125°C, VDD5V = 3.0-3.6V (3V operation) VDD5V = 4.5-5.5V (5V operation), unless otherwise noted.
6.1 Operating Conditions
6.2 DC Characteristics for Digital Inputs and Outputs
6.2.1 CMOS Schmitt-Trigger Inputs: CLK, CSn (CSn = internal Pull-up)
6.2.2 CMOS Output Open Drain: MagINCn, MagDECn
6.2.3 CMOS Output: PWM
Table 3. Operating Conditions
Symbol Parameter Note Min Typ Max Units
TAMB Ambient temperature -40°F +257°F -40 125 °C
Isupp Supply current 16 21 mA
VDD5V
VDD3V3
Supply voltage at pin VDD5V
Voltage regulator output voltage at pin
VDD3V3
5V Operation 4.5
3.0
5.0
3.3
5.5
3.6
V
V
VDD5V
VDD3V3
Supply voltage at pin VDD5V
Supply voltage at pin VDD3V3
3.3V Operation
(pin VDD5V and VDD3V3 connected)
3.0
3.0
3.3
3.3
3.6
3.6
V
V
Table 4. CMOS Schmitt-Trigger Inputs
Symbol Parameter Conditions Min Typ Max Units
VIH High level input voltage Normal operation 0.41 * VDD5V V
VIL Low level input voltage 0.13 * VDD5V V
VIon - VIoff Schmitt Trigger hysteresis 1 V
ILEAK
IiL
Input leakage current
Pull-up low level input current
CLK only -1 1 µA
CSn only, VDD5V: 5.0V -30 -100
Table 5. CMOS Output Open Drain
Symbol Parameter Conditions Min Typ Max Units
VOL Low level output voltage VSS+0.4 V
IOOutput current VDD5V: 4.5V 4 mA
VDD5V: 3V 2
IOZ Open drain leakage current 1 µA
Table 6. CMOS Output
Symbol Parameter Conditions Min Typ Max Units
VOH High level output voltage VDD5V-0.5 V
VOL Low level output voltage VSS+0.4 V
IOOutput current VDD5V: 4.5V 4 mA
VDD5V: 3V 2
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AS5311
Datasheet - Electrical Characteristics
6.2.4 Tristate CMOS Output: DO
6.3 Magnetic Input Specification
Two-pole cylindrical diametrically magnetized source:
Table 7. Tristate CMOS Output
Symbol Parameter Conditions Min Typ Max Units
VOH High level output voltage VDD5V -0.5 V
VOL Low level output voltage VSS+0.4 V
IOOutput current VDD5V: 4.5V 4 mA
VDD5V: 3V 2
Table 8. Magnetic Input Specification
Symbol Parameter Note Min Typ Max Units
LpPole length Recommended magnet: plastic or rubber
bonded ferrite or NdFeB
1mm
tmag Pole pair length 2 mm
Bpk Magnetic input field amplitude Required vertical component of the
magnetic field strength on the die’s surface 10 40 mT
Boff Magnetic offset Constant magnetic stray field ± 5 mT
Btc Magnetic field temperature drift Recommended magnet: plastic or rubber
bonded ferrite or NdFeB 0.2 %/K
Magnetic input field variation Including offset gradient ±2 %
Vabs Linear travelling speed Incremental output: 1024 steps / polepair
including interpolation1
1. 1) For absolute outputs, a practical speed limit is 2345 mm/s. At higher speeds, input signal cancellation will occur and the detected field
decreases due to the internal front-end. Significant signal change is indicated by the status bits.
2) With increasing speed, the distance between two samples increases. The travelling distance between two subsequent samples can
be calculated as:
where:
sampling_distance = travelling distance between samples (in mm)
v = travelling speed (in mm/sec)
fs = sampling rate in Hz (see Table 9)
650 mm/
sec
Disp Displacement
Maximum shift between defined Hall sensor
center and magnet centerline; depends on
magnet geometries
0.5 mm
ZDist Vertical gap Package to magnet surface;
depends on magnet strength 0.3 mm
Recommended magnet material and
temperature drift
Plastic or rubber bonded Ferrite -0.19
%/K
Plastic or rubber bonded Neodymium
(NdFeB) -0.12
sampling dist
–v
fs
----
=
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AS5311
Datasheet - Electrical Characteristics
6.4 Electrical System Specifications
Notes:
1. Integral Non-Linearity (INL) is the maximum deviation between actual position and indicated position.
2. Differential Non-Linearity (DNL) is the maximum deviation of the step length from one position to the next.
3. Transition Noise (TN) is the repeatability of an indicated position.
Table 9. Electrical System Specifications
Symbol Parameter Note Min Typ Max Units
RESabs Resolution, absolute outputs 0.488 um/step (12bit / 2mm pole pair) 12 bit /
polepair
RESinc Resolution, incremental outputs 1.95 um/step (10bit / 2mm pole pair) 10 bit /
polepair
INLopt Integral non-linearity (optimum)
Maximum error with respect to the best line
fit. Ideal magnet
TAMB =25 °C.
± 5.6 μm
INLtemp Integral non-linearity (over
temperature)
Maximum error with respect to the best line
fit. Ideal magnet
Tamb = -30 to +70 °C.
± 10 μm
DNL Differential non-linearity 10bit, no missing codes ± 0.97 μm
TN Transition noise 1 sigma 0.6 μm RMS
Von Power-on reset thresholds:
On voltage; 300mV typ. hysteresis DC supply voltage 3.3V (VDD3V3)
1.37 2.2 2.9
V
Voff Power-on reset thresholds:
Off voltage; 300mV typ. hysteresis 1.08 1.9 2.6
tPwrUp Power-up time Until status bit OCF = 1 20 ms
tdelay System propagation delay absolute
output Delay of ADC, DSP and absolute interface 96 µs
tdelay System propagation delay incremental
output Including interpolation delay at high speeds 384 µs
fSInternal sampling rate for absolute
output
TAMB = 25°C 9.90 10.42 10.94 kHz
TAMB = -40 to +125°C, 9.38 10.42 11.46
Hyst Hysteresis, incremental outputs No Hysteresis at absolute serial outputs 2 LSB
CLK Read-out frequency Maximum clock frequency to read out serial
data 1MHz
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AS5311
Datasheet - Electrical Characteristics
6.5 Timing Characteristics
6.5.1 Pulse Width Modulation Output
Table 10. Synchronous Serial Interface (SSI)
Symbol Parameter Note Min Typ Max Units
tDOactive Data output activated (logic high) Time between falling edge of CSn and data
output activated 100 ns
tCLKFE First data shifted to output register Time between falling edge of CSn and first
falling edge of CLK 500 ns
TCLK / 2 Start of data output Rising edge of CLK shifts out one bit at a time 500 ns
tDOvalid Data output valid Time between rising edge of CLK and data
output valid 413 ns
tDOtristate Data output tristate After the last bit DO changes back to “tristate” 100 ns
tCSn Pulse width of CSn CSn = high; To initiate read-out of next angular
position 500 ns
fCLK Read-out frequency Clock frequency to read out serial data >0 1 MHz
Table 11. Pulse Width Modulation Output
Symbol Parameter Note Min Typ Max Units
f PWM PWM frequency
Signal period = 4098µs ±5% at
TAMB = 25°C 232 244 256
Hz
Signal period = 4098µs ±10% at
TAMB = -40 to +125°C 220 244 268
PW MIN Minimum pulse width Position 0d = 0µm 0.9 1 1.1 µs
PW MAX Maximum pulse width Position 4095d = 1999.5µm 3892 4097 4301 µs
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AS5311
Datasheet - Detailed Description
7 Detailed Description
The different types of outputs relative to the magnet position are outlined in Figure 3 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 3. AS5311 Outputs Relative to Magnet Position
S N S NSN S N S NSN
0 … .. 4095 0 … .. 4095 0 … .. 4095 0 … .. 4095absolute output : 0 … .. 4095 0 … .. 4095
Index : 1 pulse / polepair
A : 256 pulses / polepair
B : 256 pulses / polepair
A + B = 1024 steps / polepair
2mm
PWM output : 1 … . 4097µs
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AS5311
Datasheet - Detailed Description
7.1 Incremental Outputs
Figure 4 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 4. Incremental Outputs
7.1.1 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 Electrical
System Specifications on page 8), 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 after power-up, until
CSn goes low or a low pulse is applied at CSn and internal offset compensation is finished. This mode allows intentional disabling of the
incremental outputs after power-up until for example the system microcontroller is ready to receive data.
Once the incremental outputs are unlocked they can not be disabled during operation.
Movement left to right
A
B
Incremental outputs
Index=0
1LSB
Index
Mechanical
Zero Position Movement Direction
Change
CSn
tIncremental outputs valid
Hyst =
2 LSB
Movement right to left
Mechanical
Zero Position
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AS5311
Datasheet - Detailed Description
7.2 Incremental Output Hysteresis
Figure 5. Hysteresis Illustration
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 4). 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 6. Synchronous Serial Interface with Absolute Angular Position Data
Magnet Position
Hysteresis:
2 steps
X +2
Incremental
Output
Indication
Movement left --> right
Movement right left
X +4
XX X +2 X +4 X +5
X +3
X +1
X +1
X +3
-->
D11
1
D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0 OCF COF LIN Mag
INC
Mag
DEC
Even
PAR D11
1188
tCLK FE
tCSn
tDO Tristate
Status BitsAngular Position Data
tDO valid
tDO active
TCLK/2
tCLK FE
CSn
DO
CLK
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AS5311
Datasheet - Detailed Description
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 13 for more details. For AGC algorithm only M11: M4 of the magnitude are used.
A value of zero or close to zero indicates a missing magnet.
Figure 7. Synchronous Serial Interface with Magnetic Field Strength Data
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.
After a minimum time tCLK FE, data is latched into the output shift register with the first falling edge of CLK.
Each subsequent rising CLK edge shifts out one bit of data.
The serial word contains 18 bits, if CLK is high at the falling edge of CSn (see Figure 6), the first 12 bits are the absolute distance informa-
tion 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).
If CLK is low at the falling edge of CSn, the first 12 bits contain the magnitude information and the subsequent bits contain the status bits
(see Figure 7).
A subsequent measurement is initiated by a “high” pulse at CSn with a minimum duration of tCSn.
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. If this bit is not set, the data at D11:D0
(likewise M11:M0) may be invalid.
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)
M11
1
M10 M9 M8 M7 M6 M5 M4 M3 M2 M1 M0 OCF COF LIN Mag
INC
Mag
DEC
Even
PAR D11
1188
tCLK FE
tCSn
tDO Tristate
Status BitsMagnetic field strength data
tDO valid
tDO active
TCLK/2
CSn
DO
CLK
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AS5311
Datasheet - Detailed Description
Data D11:D0 is valid, when the status bits have the following configurations:
*MagInc=MagDec=1 is only recommended in YELLOW mode (see Table 13).
7.4 Absolute Output Jitter and Hysteresis
Note: 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 Incremental Output Hysteresis. 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.
Note: 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 6).
Additionally, the LIN status bit indicates the non-recommended “red” range. The MAGnitude register provides additional information about the
strength of the magnetic field (see Figure 7). For Z-axis Range Indication only M11:M4 of the magnitude are used.
The digital status bits MagINC, MagDec, LIN and the hardware pins MagINCn, MagDECn have the following function:
Table 12. Status Bit Outputs
OCF COF LIN MagINC MagDEC Parity
10 0
00
Even checksum of bits 1:17
01
10
1* 1*
Table 13. Magnetic Field Strength Red-Yellow-Green Indicators
Status Bits MAG Hardware Pins
MagINC MagDEC LIN M11…M4 MagINCn MagDECn Description
0003F hexOffOff
No distance change
Magnetic input field OK (GREEN range, ~10…40mT peak amplitude)
0103F hexOffOff
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.
1003F hexOffOff
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.
110
20 hex-
5F 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.
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AS5311
Datasheet - Detailed Description
7.6 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:
(EQ 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 8. PWM Output Signal
111
<20 hex
>5F hex On On
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.
All other combinations n/a n/a Not available
Table 13. Magnetic Field Strength Red-Yellow-Green Indicators
Status Bits MAG Hardware Pins
MagINC MagDEC LIN M11…M4 MagINCn MagDECn Description
⋅
1/fPWM
Position
1999.5µm
(Pos 4095)
0µm
(Pos 0)
1µs 4098 µs
PWMIN
PWMAX
409 7 µs
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AS5311
Datasheet - Detailed Description
7.7 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 Low-Dropout (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 9).
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.
Figure 9. Connections for 5V and 3.3V Supply Voltages
LDO
I
N
T
E
R
F
A
C
E
2.2 ... 10 µF
100 n
4. 5 - 5.5V
VDD3V3
VSS
VDD5V
5V Operation
Internal
VDD LDO
100 n
3. 0 - 3.6V
VDD 3 V 3
VSS
VDD 5 V
3.3V Operation
Internal
VDD
I
N
T
E
R
F
A
C
E
Prog Prog
AS5311 AS5311
PWM
Index
B
A
CSn
CLK
DO
PWM
Index
B
A
CSn
CLK
DO
www.austriamicrosystems.com/AS5311 Revision 1.9 17 - 28
AS5311
Datasheet - Application Information
8 Application Information
Figure 10. AS5311 with Multi-pole Magnetic Strip for Linear Motion Sensing
Figure 11. AS5311 with Multi-pole Ring Magnets for Off-axis Rotary Motion Sensing
www.austriamicrosystems.com/AS5311 Revision 1.9 18 - 28
AS5311
Datasheet - Application Information
8.1 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 non-linearities.
Figure 12. Additional Error from Pole Length Mismatch
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 Electrical System Specifications on page 8). 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.
8.2 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.
AS5311 Systematic Linearity Error Caused by Pole
Length Deviation
0.00
10.00
20.00
30.00
40.00
50.00
60.00
70.00
750 800 850 900 950 1000 1050 1100 1150 1200 1250
Pole Length [µm]
Error [µm]
Error [µm]
www.austriamicrosystems.com/AS5311 Revision 1.9 19 - 28
AS5311
Datasheet - Application Information
8.3 Mounting the Magnet
8.3.1 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
Electrical System Specifications on page 8).
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 Z-axis Range Indication (“Red/Yellow/Green” Indicator) on page 14 for more details.
8.3.2 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).
8.3.3 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 (EQ 2)
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).
Figure 13. Active Area of Strip Magnet
N
strip length
2mm
S N SN SNS NS
Active area
(width)
Active area ( length )
Active Area
Bpk Bpk
recommended
scanning path
B
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AS5311
Datasheet - Application Information
Figure 14. Alignment of Magnet Strip with AS5311 Sensor IC
3 . 0475 ± 0 . 235
3.2 0 0± 0.2 35
Die C / L
2.5 7 6± 0.2 35
Note : all dimensions are in mm
S N S NS NSN SN
AS 5311
Package
Outline
3 . 0475 ± 0 . 235
Die C / L
S N S NS NSN SN
leftmost magnet position
vertical airgap
1. 00
1. 00
rightmost magnet position
position value
increases
position value
decreases
see text
magnet
strip
carrier
0.2299±0.100
0.2341±0.100
..
0 7701 ± 0 150
±
1.00 0.1
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AS5311
Datasheet - Application Information
8.4 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 non-linearities, the second pole (2…4mm) is very precise, etc.
Figure 15. Sample Test Results of INL at Different Airgaps
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.
INL MS10-10
-25
-20
-15
-10
-5
0
5
10
15
20
25
0 1000 2000 3000 4000 5000 6000 7000 8000
X [µm]
Error [µm]
z= 200µ
z= 400µ
www.austriamicrosystems.com/AS5311 Revision 1.9 22 - 28
AS5311
Datasheet - Application Information
8.5 AS5311 Off-axis Rotary Applications
The AS5311 can also be used as an off-axis rotary encoder, as shown in Figure 11. 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 vs. 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.
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.
Res [bit] Steps per Revolution Ring Diameter [mm] Maximum Speed [rpm]
15 32768 20.9 609
16 65536 41.7 305
17 131072 83.4 152
AS5311 off-axis rotary resolution & speed
0
20000
40000
60000
80000
100000
120000
140000
160000
20 40 60 80 100
ring diameter [mm]
resolution [steps / rev]
0
100
200
300
400
500
600
700
max. speed [rpm]
resolution
speed rpm
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AS5311
Datasheet - Application Information
The number of incremental steps per revolution can be calculated as:
(EQ 3)
(EQ 4)
Note: 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:
(EQ 5)
The maximum rotational speed can be calculated as:
(EQ 6)
Where:
nbr_polepairs is the number of pole pairs at the magnet ring.
d is the diameter of the ring in mm; the diameter is taken at the locus of the Hall elements underneath the magnet.
max_rot_speed is the maximum rotational speed in revolutions per minute rpm.
max_lin_speed is the 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.
polepairsnbrstepslincrementa _*1024_
=
2
**1024
_
π
d
stepslincrementa =
π
mmpolepairsnbr
d2*_
=
ππ
*
39000
*
60*_max_
_max_ dd
speedlin
speedrot ==
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AS5311
Datasheet - Package Drawings and Markings
9 Package Drawings and Markings
The device is available in a 20-pin TSSOP package.
Figure 17. 20-pin TSSOP Package Dimensions and Hall Array Location
Symbol Min Nom Max
A- - 1.20
A1 0.05 - 0.15
A2 0.80 1.00 1.05
b0.19 - 0.30
c0.09 - 0.20
D 6.40 6.50 6.60
E - 6.40 BSC -
E1 4.30 4.40 4.50
e-
0.65 BSC -
L 0.45 0.60 0.75
L1 - 1.00 REF -
R0.09 - -
R1 0.09 - -
S0.20 - -
θ1 0° - 8°
θ2 -12 REF-
θ3 -12 REF-
aaa - 0.10 -
bbb - 0.10 -
ccc - 0.05 -
ddd - 0.20 -
N20
Notes:
1. Dimensions & Tolerancing confirm to ASME Y14.5M-1994.
2. All dimensions are in millimeters. Angles are in degrees.
AS5311
YYWWMZZ @
Pin 1 identification
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AS5311
Datasheet - Package Drawings and Markings
Marking: YYWWMZZ.
Note: IC's marked with a white dot or the letters "ES" denote Engineering Samples.
JEDEC Package Outline Standard: MO - 153
Thermal Resistance Rth(j-a): 89 K/W in still air, soldered on PCB
9.1 Recommended PCB Footprint
Figure 18. PCB Footprint
YY WW MZZ @
Year Manufacturing Week Plant Identifier Traceability Code Sublot Identifier
Recommended Footprint Data
Symbol mm inch
A7.000.276
B5.000.197
C0.380.015
D0.650.026
E6.230.245
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AS5311
Datasheet - Revision History
Revision History
Note: Typos may not be explicitly mentioned under revision history.
Revision Date Owner Description
1.1 26 Jun, 2009 jja / jlu Recommended PCB Footprint (page 25) updated
1.2 09 Apr, 2010 agt Ordering Information (page 27) updated
1.3 24 Sep, 2010 Updated Figure 7
1.6 08 Nov, 2011
rph
Added few lines in Magnetic Input Specification (page 7) and edited the
footnote in Data Contents (page 13)
1.7 01 Mar, 2012 Updated Figure 7 and Section 7.1.1 and Section 7.3
1.8 12 Mar, 2012 Updated Package Drawings and Markings, Absolute Maximum Ratings,
Figure 14 and Ordering Information
1.9 11 Apr, 2012 Updated Ordering Information, General Description and Pin Descriptions
www.austriamicrosystems.com/AS5311 Revision 1.9 27 - 28
AS5311
Datasheet - Ordering Information
10 Ordering Information
The devices are available as the standard products shown in Table 14.
Note: All products are RoHS compliant and austriamicrosystems green.
Buy our products or get free samples online at ICdirect: http://www.austriamicrosystems.com/ICdirect
For further information and requests, please contact us mailto:sales@austriamicrosystems.com
or find your local distributor at http://www.austriamicrosystems.com/distributor
Table 14. Ordering Information
Ordering Code Description Delivery Form Package
AS5311-ATSU 1 box = 100 tubes à 74 devices Tubes
20-pin TSSOP
AS5311-ATST 1 reel = 1000 devices
1 reel = 4500 devices Tape & Reel
www.austriamicrosystems.com/AS5311 Revision 1.9 28 - 28
AS5311
Datasheet - Copyrights
Copyrights
Copyright © 1997-2012, austriamicrosystems AG, Tobelbaderstrasse 30, 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.
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 life-sustaining equipment are
specifically not recommended without additional processing by austriamicrosystems AG for each application. For shipments of less than 100
parts the manufacturing flow might show deviations from the standard production flow, such as test flow or test location.
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
Tobelbaderstrasse 30
A-8141 Unterpremstaetten, 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