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AS5311 Data Sheet
AS5311
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 <0.5m. 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 m 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 with Multi-pole Magnetic Strip for Linear Motion Sensing
Preliminary Data Sheet
The AS5311 is available in a Pb-free TSSOP-20 package and qualified for an ambient temperature range from -40C to +125C.
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
Figure 2: Block Diagram of AS5311
VDD3V3 MagINCn VDD5V MagDECn
PWM Sin Ang DO Cos Mag 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 2 3 4 5 General Description ...................................................................................................................... 1 Key Features ................................................................................................................................ 1 Applications.................................................................................................................................. 1 Table of Contents ......................................................................................................................... 3 Pinout .......................................................................................................................................... 5 5.1 5.2 6 Pin Assignments ..................................................................................................................... 5 Pin Description ....................................................................................................................... 5
Electrical Characteristics............................................................................................................... 6 6.1 6.2 6.3 Absolute Maximum Ratings ..................................................................................................... 6 Operating Conditions .............................................................................................................. 7 DC Characteristics for Digital Inputs and Outputs ..................................................................... 7 CMOS Schmitt-Trigger Inputs: CLK, CSn (CSn = internal Pull-up) ....................................... 7 CMOS Output Open Drain: MagINCn, MagDECn ................................................................ 7 CMOS Output: PWM ......................................................................................................... 7 Tristate CMOS Output: DO ................................................................................................ 8
6.3.1 6.3.2 6.3.3 6.3.4 6.4 6.5 6.6
Magnetic Input Specification.................................................................................................... 8 Electrical System Specifications .............................................................................................. 8 Timing Characteristics ............................................................................................................ 9 Synchronous Serial Interface (SSI) .................................................................................... 9 Pulse Width Modulation Output........................................................................................ 10
6.6.1 6.6.2 7
Detailed Description.................................................................................................................... 10 7.1 Incremental Outputs.............................................................................................................. 11 Incremental Power-up Lock Option .................................................................................. 11
7.1.1 7.2 7.3
Incremental Output Hysteresis............................................................................................... 12 Synchronous Serial Interface (SSI) ........................................................................................ 12 Data Contents ................................................................................................................ 13
7.3.1 7.4
Absolute Output Jitter and Hysteresis .................................................................................... 14 Adding a Digital Hysteresis ............................................................................................. 14 Implementing Digital Filtering .......................................................................................... 14
7.4.1 7.4.2 7.5 8 9 10
Z-axis Range Indication ("Red/Yellow/Green" Indicator) .......................................................... 14
Pulse Width Modulation (PWM) Output ........................................................................................ 15 3.3V / 5V Operation .................................................................................................................... 15 Magnet Specifications .............................................................................................................. 16 Magnetization .................................................................................................................... 16 Position of the Index Pulse ................................................................................................. 17 Mounting the Magnet ......................................................................................................... 17 Vertical Distance ......................................................................................................... 17 Alignment of Multi-pole Magnet and IC.......................................................................... 17 Lateral stroke of Multi-pole Strip Magnets ..................................................................... 17
10.1 10.2 10.3
10.3.1 10.3.2 10.3.3 11
Measurement Data Example ..................................................................................................... 19
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AS5311 Data Sheet
12 13 14 15 16 17 18
AS5311 Off-axis Rotary Applications ........................................................................................ 20 Package Drawings and Marking ................................................................................................ 21 Ordering Information ................................................................................................................ 22 Recommended PCB Footprint................................................................................................... 22 Revision History ...................................................................................................................... 23 Copyrights ............................................................................................................................... 23 Disclaimer ............................................................................................................................... 23
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AS5311 Data Sheet
5 Pinout
5.1 Pin Assignments
Figure 4: AS5311 Pin Configuration, TSSOP-20
NC MagIncn MagDecn A B NC Index VSS Prog NC
1 2 3 4 5 6 7 8 9 10
20 19 18
NC VDD5V VDD3V3 NC NC PWM CSn CLK DO NC
AS5311
17 16 15 14 13 12 11
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 1.95m. 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 22...10F 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 1s pulse width per step (1s to 4097s 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 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 DO_OD DO DI_PD DI_PU
Pin Description Symbol NC MagINCn MagDECn A B NC Index VSS Prog NC NC DO CLK CSn PWM NC NC VDD3V3 VDD5V NC digital digital digital digital Type DO_OD DO_OD DO DO DO S DI_PD DO_T DI, ST DI_PU, ST DO S S Must be left unconnected Magnet Field Magnitude INCrease; active low, indicates a distance reduction between the magnet and the device surface. Magnet Field Magnitude DECrease; active low, indicates a distance increase between the device and the magnet. Incremental output A Incremental output B Must be left unconnected Incremental output Index. Negative Supply Voltage (GND) OTP Programming Input for factory programming. Connect to VSS Must be left unconnected Must be left unconnected Data Output of Synchronous Serial Interface Clock Input of Synchronous Serial Interface; Schmitt-Trigger input Chip Select, active low; Schmitt-Trigger input, internal pull-up resistor (~50k). Must be low to enable incremental outputs Pulse Width Modulation of approx. 244Hz; 1s/step Must be left unconnected Must be left unconnected 3V-Regulator output; internally regulated from VDD5V. Connect to VDD5V for 3V supply voltage. Do not load externally. Positive Supply Voltage, 3.0 to 5.5 V Must be left unconnected S DI DO_T ST supply pin digital input digital output /tri-state Schmitt-Trigger input Description
output open drain output input pull-down input pull-up
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 DC supply voltage at pin VDD5V DC supply voltage at pin VDD3V3 Input pin voltage Input current (latchup immunity) Electrostatic discharge Storage temperature -55 -0.3 -100 Min -0.3 Max 7 5 VDD5V +0.3 100 2 125 Unit V V V mA kV C Except VDD3V3 Norm: JEDEC 78 Norm: MIL 883 E method 3015 Min - 67F ; Max +257F Comments
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AS5311 Data Sheet
Parameter Body temperature (Lead-free package) Humidity non-condensing
Min
Max 260
Unit C %
Comments t=20 to 40s, Norm: IPC/JEDEC J-Std-020C Lead finish 100% Sn "matte tin"
5
85
6.2 Operating Conditions
Table 3 Operating Conditions Parameter Ambient temperature Supply current Supply voltage at pin VDD5V Voltage regulator output voltage at pin VDD3V3 Supply voltage at pin VDD5V Supply voltage at pin VDD3V3 Symbol Tamb Isupp VDD5V VDD3V3 VDD5V VDD3V3 4.5 3.0 3.0 3.0 Min -40 16 5.0 3.3 3.3 3.3 Typ Max 125 21 5.5 3.6 3.6 3.6 Unit C mA V V V V 5V Operation 3.3V Operation (pin VDD5V and VDD3V3 connected) Note -40F...+257F
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 +125C, VDD5V = 3.0-3.6V (3V operation) VDD5V = 4.5-5.5V (5V operation) unless otherwise noted.
Parameter High level input voltage Low level input voltage Schmitt Trigger hysteresis Input leakage current Pull-up low level input current
Symbol VIH VIL VIon - VIoff ILEAK IiL
Min 0.41 * VDD5V
Max 0.13 * VDD5V
Unit V V V CLK only
Note Normal operation
1 -1 -30 1 -100
A
CSn only, VDD5V: 5.0V
6.3.2
CMOS Output Open Drain: MagINCn, MagDECn
Operating conditions: Tamb = -40 to +125C, 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
Symbol VOL IO IOZ
Min
Max VSS+0.4 4 2 1
Unit V mA A
Note VDD5V: 4.5V VDD5V: 3V
6.3.3
CMOS Output: PWM
Operating conditions: Tamb = -40 to +125C, VDD5V = 3.0-3.6V (3V operation) VDD5V = 4.5-5.5V (5V operation) unless otherwise noted.
Parameter High level output voltage Low level output voltage Output current
Symbol VOH VOL IO
Min VDD5V-0.5
Max VSS+0.4 4 2
Unit V V mA mA
Note
VDD5V: 4.5V VDD5V: 3V
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AS5311 Data Sheet
6.3.4
Tristate CMOS Output: DO
Operating conditions: Tamb = -40 to +125C, VDD5V = 3.0-3.6V (3V operation) VDD5V = 4.5-5.5V (5V operation) unless otherwise noted.
Parameter High level output voltage Low level output voltage Output current
Symbol VOH VOL IO
Min VDD5V -0.5
Max VSS+0.4 4 2
Unit V V mA mA
Note
VDD5V: 4.5V VDD5V: 3V
6.4 Magnetic Input Specification
Operating conditions: Tamb = -40 to +125C, VDD5V = 3.0-3.6V (3V operation) VDD5V = 4.5 - 5.5V (5V operation) unless otherwise noted.
Two-pole cylindrical diametrically magnetised source: Parameter Pole length Pole pair length Magnetic input field amplitude Magnetic offset Magnetic field temperature drift Magnetic input field variation Linear travelling speed Vabs Symbol Lp tmag Bpk Boff Btc 10 Min Typ 1 2 40 5 0.2 2 650 Max Unit mm mm mT mT %/K % mm/ sec mm mm %/K Note Recommended magnet: plastic or rubber bonded ferrite or NdFeB Required vertical component of the magnetic field strength on the die's surface Constant magnetic stray field Recommended magnet: plastic or rubber bonded ferrite or NdFeB Including offset gradient Incremental output: 1024 steps / polepair including interpolation 1) Max. shift between defined Hall sensor center and magnet centerline (see Figure 17); depends on magnet geometries Package to magnet surface; depends on magnet strength Plastic or rubber bonded Ferrite Plastic or rubber bonded Neodymium (NdFeB)
Displacement Vertical gap Recommended magnet material and temperature drift
Disp ZDist
0.5 0.3 -0.19 -0.12
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 +125C, VDD5V = 3.0~3.6V (3V operation) VDD5V = 4.5~5.5V (5V operation) unless otherwise noted.
Parameter Resolution, absolute outputs Resolution, incremental outputs Integral non-linearity (optimum)
Symbol RESabs RESinc INLopt
Min
Typ 12 10
Max
Unit bit / polepair bit / polepair
Note 0.488 um/step (12bit / 2mm pole pair) 1.95 um/step (10bit / 2mm pole pair) Maximum error with respect to the best line fit. Ideal magnet Tamb =25 C.
5.6
m
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AS5311 Data Sheet
Parameter Integral non-linearity (over temperature) Differential non-linearity Transition noise Power-on reset thresholds On voltage; 300mV typ. hysteresis Off voltage; 300mV typ. hysteresis Power-up time System propagation delay absolute output : System propagation delay incremental output Internal sampling rate for absolute output Hysteresis, incremental outputs Read-out frequency
Symbol INLtemp DNL TN Von Voff tPwrUp tdelay tdelay fS Hyst CLK
Min
Typ
Max 10 0.97 0.6
Unit m m m RMS
Note Maximum error with respect to the best line fit. Ideal magnet Tamb = -30 to +70 C. 10bit, no missing codes 1 sigma DC supply voltage 3.3V (VDD3V3)
1.37 1.08
2.2 1.9
2.9 V 2.6 20 96 384 ms s s kHz LSB 1 MHz
DC supply voltage 3.3V (VDD3V3) Until status bit OCF = 1 Delay of ADC, DSP and absolute interface Including interpolation delay at high speeds Tamb = 25C Tamb = -40 to +125C, No Hysteresis at absolute serial outputs Max. clock frequency to read out serial data
9.90 9.38
10.42 10.42 2
10.94 11.46
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 +125C, VDD5V = 3.0~3.6V (3V operation) VDD5V = 4.5~5.5V (5V operation) unless otherwise noted.
Parameter Data output activated (logic high) First data shifted to output register Start of data output Data output valid Data output tristate Pulse width of CSn Read-out frequency
Symbol t DO active tCLK FE T CLK / 2 t DO valid t DO tristate t CSn fCLK
Min
Typ
Max 100
Unit ns ns ns
Note Time between falling edge of CSn and data output activated Time between falling edge of CSn and first falling edge of CLK Rising edge of CLK shifts out one bit at a time Time between rising edge of CLK and data output valid After the last bit DO changes back to "tristate" CSn = high; To initiate read-out of next angular position Clock frequency to read out serial data
500 500 413 100 500 >0 1
ns ns ns MHz
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AS5311 Data Sheet
6.6.2
Pulse Width Modulation Output
Operating conditions: Tamb = -40 to +125C, VDD5V = 3.0~3.6V (3V operation) VDD5V = 4.5~5.5V (5V operation) unless otherwise noted.
Parameter PWM frequency Minimum pulse width Maximum pulse width
Symbol f PWM PW MIN PW MAX
Min 232 220 0.9 3892
Typ 244 244 1 4097
Max 256 268 1.1 4301
Unit Hz s s
Note Signal period = 4098s 5% at Tamb = 25C = 4098s 10% at Tamb = -40 to +125C Position 0d =0m Position 4095d = 1999.5m
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 1s, increases the pulse width with every step of 0.488m and reaches a maximum pulse width of 4097s 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
Increm en tal o utputs
A B
M echanical Z ero P osition
M ovem ent Direction Change
M echanical Zero Position
Index= 0 1 LSB
In d e x
H y st = 2 LSB Movement left to right
CS n
t
In cre m e n tal o u tp u ts va lid
Movem ent right to left
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 5k). 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 X +3 X +2 X +1 X
X X +1 X +2 X +3 X +4 X +5 Magnet Position
Hysteresis: 2 steps
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 (2000m / 4096) per step. CLK must be high at the falling edge of CSn. Figure 8: Synchronous Serial Interface with Absolute Angular Position Data
CSn
tCLK FE TCLK/2 1 8 18 tCSn 1 tCLK FE
CLK
DO
D11
D10
D9
D8
D7
D6
D5
D4
D3
D2
D1
D0
OCF
COF
LIN
Mag INC
Mag DEC
Even PAR
D11
tDO active
tDO valid Angular Position Data Status Bits
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
CSn
TCLK/2 tCSn 8 18 1 tCLK FE
CLK
1
DO
0
0 tDO valid
0
0
0
M6
M5
M4
M3
M2
M1
M0
OCF
COF
LIN
Mag INC
Mag DEC
Even PAR
D11
tDO active
Magnetic field strength data
Status Bits
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. After a minimum time t CLK 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 (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). 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) 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 COF LIN Mag INC 0 1 0 0 0 1 1*) Mag DEC 0 1 0 1*) even checksum of bits 1:15 Parity
*) 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 (=3.9m) 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 INC 0 Mag DEC 0 LIN MAG M11.. M0 3F hex Mag INCn Off Mag DECn Off Hardware Pins Description No distance change Magnetic input field OK ( GREEN range, ~10...40mT peak amplitude) 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. 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. YELLOW range: magnetic field is ~3.4....54.5mT. The AS5311 may still be operated in this range, but with slightly reduced accuracy. 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
0
0
1
0
3F hex
Off
Off
1
0
0
3F hex 20 hex5F hex <20 hex >5F hex
Off
Off
1
1
0
On
Off
1
1
1
On n/a
On n/a
All other combinations
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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
A linear position of 1999.5m = digital position 4095 will generate a pulse width of ton = 4097s and a pause toff = 1s
for digital position = 0 - 4094 Exception:
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 0m (Pos 0)
PW MIN
1s
4098s
PWMAX 1999.5m (Pos 4095)
4097s
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...10F 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
2.2...10F
3.3V Operation
VDD3V3 VDD3V3
100n
100n
VDD5V
LDO
Internal VDD PWM DO
VDD5V
LDO
Internal VDD PWM
4.5 - 5.5V
Prog VSS
I N T E R F A C E
3.0 - 3.6V
CLK CSn A B Index Prog VSS
I N T E R F A C E
DO CLK CSn A B Index
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 [m] 40.00 30.00 20.00 10.00 0.00 750 800 850 900 950 1000 1050 1100 1150 1200 1250 Pole Length [m] 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 50m. 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.
Error [m]
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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 1/2 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). Figure 13: Active Area of Strip Magnet
Bpk Bpk
Active Area
B
Active area (length)
Active area (width)
N
S
N
S
N
S
N
S
N
S
recommended scanning path
2mm
strip length
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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
N
3.04750.235
1.00
AS5311 Package Outline
rightmost magnet position
Die C/L
position value decreases
3.2000.235
2.5760.235
S
N
S
N
S
N
S
N
S
N
1.00 3.04750.235
vertical airgap magnet strip carrier
see text
1.00 0.1
Note: all dimensions are in mm
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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 +/- 10m) 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... Figure 15: Sample Test Results of INL at Different Airgaps
25 20 15 10 5 0 -5 -10 -15 -20 -25 0 1000 2000 3000
INL MS10-10
z= 200 z= 400
Error [m]
4000
X [m]
5000
6000
7000
8000
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
AS5311 off-axis rotary resolution & speed
160000 140000 120000
resolution [steps / rev]
700 resolution speed rpm 600 500 400
max. speed [rpm]
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
100000 80000 300 60000 40000 20000 0 20 40 60
ring diameter [mm]
200 100 0 80 100
Res [bit] 15 16 17
Steps / Rev. 32768 65536 131072
Ring Diameter [mm] 20.9 41.7 83.4
Max Speed [rpm] 609 305 152
The number of incremental steps per revolution can be calculated as:
incremental _ steps = 1024 * nbr _ polepairs
incremental _ steps = 1024 * d * 2
Note that the circumference (d*) 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
The maximum rotational speed can be calculated as:
max_ rot _ speed =
where nbr_polepairs d
max_ lin _ speed * 60 39000 = d * 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) 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
Note:
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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
0.22990.100 Die C/L 0.23410.100 3.2000.235 2.5760.235
Package Outline
0.77010.150 3.04750.235
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AS5311 Data Sheet
Dimensions
Symbol A A1 A2 b c D E E1 e K L 0 0.50 mm Min 0.05 0.85 0.19 0.09 6.40 6.20 4.30 Typ 0.90 6.50 6.40 4.40 0.65 0.60 Max 1.10 0.15 0.95 0.30 0.20 6.60 6.60 4.50 8 0.75 0.244 0.169 0 0.019 0.252 0.173 .0256 0.024 8 0.030 0.260 0.177 Min 0.002 0.033 0.007 0.004 inch Typ 0.035 Max 0.043 0.006 0.037 0.012 0.008
Marking: AYWWIZZ
A: Pb-Free Identifier Y: Last Digit of Manufacturing Year WW: Manufacturing Week I: Plant Identifier ZZ: Traceability Code JEDEC Package Outline Standard: MO - 153 Thermal Resistance Rth(j-a): 89 K/W in still air, soldered on PCB. 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 a 77 devices) for delivery in tubes for delivery in tape and reel
Order # AS5311ASSU Order # AS5311ASST
15 Recommended PCB Footprint
Recommended Footprint Data A B C D E mm 7.00 5.00 0.38 0.65 6.23 inch 0.276 0.197 0.015 0.026 0.245
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AS5311 Data Sheet
16 Revision History
Revision 1.01 Date 26-Jun-09 Owner jja, jlu Description Recommended footprint data updated
17 Copyrights
Copyright (c) 2009, austriamicrosystems AG, Schloss Premstaetten, 8141 Unterpremstaetten, Austria - Europe. Trademarks Registered (R). 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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