AS5311-ATST

AS5311 Data Sheet AS5311 Preliminary Data Sheet High Resolution Magnetic Linear Encoder 1 General Description The AS5311 is a contactless high resolution magnetic linear encoder for accurate linear motion and off-axis rotary sensing with a resolution down to 0 MHz Clock frequency to read out serial data www.austriamicrosystems.com 1 Revision 1.04 9 - 24 AS5311 Data Sheet 6.6.2 Pulse Width Modulation Output Operating conditions: Tamb = -40 to +125°C, VDD5V = 3.0~3.6V (3V operation) VD D5V = 4.5~5.5V (5V operation) unless otherwise noted. Parameter PWM frequency Symbol f PWM Min Typ Max 232 244 256 Unit Hz Note Signal period = 4098µs ±5% at Tamb = 25°C = 4098µs ±10% at Tamb = -40 to +125°C 220 244 268 Minimum pulse width PW MIN 0.9 1 1.1 µs Position 0d =0µm Maximum pulse width PW MAX 3892 4097 4301 µs Position 4095d = 1999.5µm 7 Detailed Description The different types of outputs relative to the magnet position are outlined in Figure 5 below. The absolute serial output counts from 0….4095 within one pole pair and repeats with each subsequent pole pair. Likewise, the PWM output starts with a pulse width of 1µs, increases the pulse width with every step of 0.488µm and reaches a maximum pulse width of 4097µs at the end of each pole pair. An index pulse is generated once for every pole pair. 256 incremental pulses are generated at each output A and B for every pole pair. The outputs A and B are phase shifted by 90 electrical degrees, which results in 1024 edges per pole pair. As the incremental outputs are also repeated with every pole pair, a constant train of pulses is generated as the magnet moves over the chip. Figure 5. AS5311 Outputs Relative to Magnet Position www.austriamicrosystems.com Revision 1.04 10 - 24 AS5311 Data Sheet 7.1 Incremental Outputs Figure 6 shows the two-channel quadrature output of the AS5311. Output A leads output B when the magnet is moving from right to left and output B leads output A when the magnet is moving from left to right (see Figure 14). Figure 6. Incremental Outputs M echanical Z ero P osition Increm en tal outputs M ovem ent Direction Change M echanical Zero Position A B Index= 0 1 LSB In d e x Movem ent righ t to left CS n t 7.1.1 H y st = 2 LSB Mo vem en t le ft to righ t In cre m e n tal o u tp u ts va lid Incremental Power-up Lock Option After power-up, the incremental outputs can optionally be locked or unlocked, depending on the status of the CSn pin: CSn = low at power-up: CSn has an internal pull-up resistor and must be externally pulled low (Rext ≤ 5kΩ). If Csn is low at power-up, the incremental outputs A, B and Index will be high until the internal offset compensation is finished. This unique state may be used as an indicator for the external controller to shorten the waiting time at power-up. Instead of waiting for the specified maximum power up-time (see 6.5), the controller can start requesting data from the AS5311 as soon as the state (A=B=Index = high) is cleared. CSn = high or open at power-up: In this mode, the incremental outputs (A, B, Index) will remain at logic high state, until CSn goes low or a low pulse is applied at CSn. This mode allows intentional disabling of the incremental outputs until for example the system microcontroller is ready to receive data. www.austriamicrosystems.com Revision 1.04 11 - 24 AS5311 Data Sheet 7.2 Incremental Output Hysteresis Figure 7. Hysteresis Illustration Incremental Output Indication X +4 Hysteresis: 2 steps X +3 X +2 X +1 X X Magnet Position X +1 X +2 X +3 X +4 X +5 Movement left -> right Movement right -> left To avoid flickering incremental outputs at a stationary magnet position, a hysteresis is introduced. In case of a movement direction change, the incremental outputs have a hysteresis of 2 LSB. For constant movement directions, every magnet position change is indicated at the incremental outputs (see Figure 6). If for example the magnet moves from position „x+3“ to „x+4“, the incremental output would also indicate this position accordingly. A change of the magnet’s movement direction back to position „x+3“ means, that the incremental output still remains unchanged for the duration of 2 LSB, until position „x+2“ is reached. Following this movement, the incremental outputs will again be updated with every change of the magnet position. 7.3 Synchronous Serial Interface (SSI) The Serial interface allows data transmission of the 12-bit absolute linear position information (within one pole pair = 2.0mm). Data bits D11:D0 represent the position information with a resolution of 488nm (2000µm / 4096) per step. CLK must be high at the falling edge of CSn. Figure 8. Synchronous Serial Interface with Absolute Angular Position Data tCLK FE CSn TCLK/2 tCLK FE tCSn 1 CLK DO 8 D11 tDO active D10 D9 D8 D7 D6 D5 D4 18 D3 D2 D1 D0 OCF COF LIN Mag INC tDO valid Angular Position Data Status Bits Mag DEC 1 Even PAR D11 tDO Tristate If CLK is low at the falling edge of CSn, the first 12 bits represent the magnitude information, which is proportional to the magnetic field strength. This information can be used to detect the presence and proper distance of the magnetic strip by comparing it to a known good value (depends on the magnet material and distance). The automatic gain control (AGC) maintains a constant MAGnitude value of 3F hex (=”green” range). If the MAG value is 3F hex, the AGC is out of the regulating range (“yellow” or “red” range). See Table 5 for more details. www.austriamicrosystems.com Revision 1.04 12 - 24 AS5311 Data Sheet A value of zero or close to zero indicates a missing magnet. Figure 9. Synchronous Serial Interface with Magnetic Field Strength Data tCLK FE CSn TCLK/2 tCSn 1 CLK DO 8 M11 M10 M9 M8 M7 M6 M5 M4 18 M3 M2 M1 M0 OCF COF LIN Mag INC Mag DEC 1 Even PAR D11 tDO valid tDO active tDO Tristate Magnetic field strength data Status Bits 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 t CSn. 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 Over flow), logic high indicates an out of range error in the CORDIC part. When this bit is set, the data at D11:D0 (likewise M11:M0) is invalid. This alarm may be resolved by bringing the magnet within the X-Y-Z tolerance limits. LIN (Linearity Alarm), logic high indicates that the input field generates a critical output linearity. When this bit is set, the data at D11:D0 may still be used, but can contain invalid data. This warning can be resolved by increasing the magnetic field strength. Even Parity bit for transmission error detection of bits 1…17 (D11…D0, OCF, COF, LIN, MagINC, MagDEC) Data D11:D0 is valid, when the status bits have the following configurations: Table 4. Status Bit Outputs OCF 1 COF 0 LIN 0 Mag INC Mag DEC 0 0 0 1 1 0 1*) 1*) Parity even checksum of bits 1:17 *) MagInc=MagDec=1 is only recommended in YELLOW mode (see Table 5) www.austriamicrosystems.com Revision 1.04 13 - 24 AS5311 Data Sheet 7.4 Absolute Output Jitter and Hysteresis Note that there is no hysteresis or additional filtering at the absolute output. This allows a determination of the magnet’s absolute position within one pole pair down to submicron range. Due to the intentionally omitted hysteresis and due to noise (e.g. from weak magnetic fields), the absolute output may jitter when the magnet is stationary over the chip. In order to get a stable 12-bit absolute reading, two common methods may be implemented to reduce the jitter. 7.4.1 Adding a Digital Hysteresis The hysteresis feature of the incremental outputs is described in 7.2. An equivalent function can be implemented in the software of the external microcontroller. The hysteresis should be larger than the peak-to-peak noise (=jitter) of the absolute output in order to mask it and create a stable output reading. Remark: the 2-bit hysteresis on the incremental output (=3.9µm) is equivalent to a hysteresis of 8LSB on the absolute output. 7.4.2 Implementing Digital Filtering Another useful alternative or additional method to reduce jitter is digital filtering. This can be accomplished simply by averaging, for example a moving average calculation in the external microcontroller. Averaging 4 readings results in 6dB (=50%) noise and jitter reduction. An average of 16 readings reduces the jitter by a factor of 4. Averaging causes additional latency of the processed data. Therefore it may be useful to adjust the depth of averaging depending on speed of travel. For example using a larger depth when the magnet is stationary and reducing the depth when the magnet is in motion. 7.5 Z-axis Range Indication (“Red/Yellow/Green” Indicator) The AS5311 provides several options of detecting the magnet distance by indicating the strength of the magnetic field. Signal indicators MagINCn and MagDECn are available both as hardware pins (pins 1 and 2) and as status bits in the serial data stream (see Figure 8). Additionally the LIN status bit indicates the nonrecommended “red” range. The MAGnitude register provides additional information about the strength of the magnetic field (see Figure 9). The digital status bits MagINC, MagDec, LIN and the hardware pins MagINCn, MagDECn have the following function: Table 5. Magnetic Field Strength Red-Yellow-Green Indicators Status Bits MAG Hardware Pins Mag INC Mag DEC LIN M11.. M0 Mag INCn Mag DECn 0 0 0 3F hex Off Off No distance change Magnetic input field OK ( GREEN range, ~10…40mT peak amplitude) 0 1 0 3F hex Off Off Distance increase; this state is a dynamic state and only active while the magnet is moving away from the chip. Magnitude register may change but regulates back to 3F hex. 1 0 0 3F hex Off Off Distance decrease; this state is a dynamic state and only active while the magnet is moving towards the chip. Magnitude register may change but regulates back to 3F hex. 1 1 0 20 hex5F hex On Off YELLOW range: magnetic field is ~3.4….54.5mT. The AS5311 may still be operated in this range, but with slightly reduced accuracy. 1 5F hex 1 1 All other combinations www.austriamicrosystems.com On On n/a n/a Description RED range: magnetic field is 5F). It is still possible to operate the AS5311 in the red range, but not recommended. Not available Revision 1.04 14 - 24 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 (t on + toff ) − 1 for digital position = 0 – 4094 Exception: A linear position of 1999.5µm = digital position 4095 will generate a pulse width of t on = 4097µs and a pause toff = 1µs The PWM frequency is internally trimmed to an accuracy of ±5% ( ±10% over full temperature range). This tolerance can be cancelled by measuring the complete duty cycle as shown above. Figure 10. PWM Output Signal Position PW MIN 0µm (Pos 0) 1µs 4098µs PW MA X 1999.5µm (Pos 4095) 4097µs 1/fPWM 9 3.3V / 5V Operation The AS5311 operates either at 3.3V ±10% or at 5V ±10%. This is made possible by an internal 3.3V LowDropout (LDO) Voltage regulator. The internal supply voltage is always taken from the output of the LDO, meaning that the internal blocks are always operating at 3.3V. For 3.3V operation, the LDO must be bypassed by connecting VDD3V3 with VDD5V (see Figure 11). For 5V operation, the 5V supply is connected to pin VDD5V, while VDD3V3 (LDO output) must be buffered by a 2.2...10µF capacitor, which is supposed to be placed close to the supply pin. The VDD3V3 output is intended for internal use only It must not be loaded with an external load. The output voltage of the digital interface I/O’s corresponds to the voltage at pin VDD5V, as the I/O buffers are supplied from this pin. A buffer capacitor of 100nF is recommended in both cases close to pin VDD5V. Note that pin VDD3V3 must always be buffered by a capacitor. It must not be left floating, as this may cause an instable internal 3.3V supply voltage which may lead to larger than normal jitter of the measured angle. www.austriamicrosystems.com Revision 1.04 15 - 24 AS5311 Data Sheet Figure 11. Connections for 5V and 3.3V Supply Voltages 5V Operation 3.3V Operation 2.2...10µF VDD3V3 VDD3V3 100n 100n VDD5V LDO Internal VDD VDD5V LDO Internal VDD PWM I N T E R F A C E 4.5 - 5.5V Prog PWM DO 3.0 - 3.6V CLK CSn A B Prog Index VSS I N T E R F A C E DO CLK CSn A B Index VSS AS5311 AS5311 10 Magnet Specifications 10.1 Magnetization The AS5311 accepts magnetic multi-pole strip or ring magnets with a pole length of 1.0mm. Recommended magnet materials include plastic or rubber bonded ferrite or Neodymium magnets. It is not recommended to use the AS5311 with other pole lengths as this will create additional nonlinearities. Figure 12. Additional Error from Pole Length Mismatch AS5311 Systematic Linearity Error Caused by Pole Length Deviation 70.00 60.00 Error [µm] Error 50.00 [µm] 40.00 30.00 20.00 10.00 0.00 750 800 850 900 950 1000 1050 1100 1150 1200 1250 Pole Length [µm] Figure 12 shows the error caused by a mismatch of pole length. Note that this error is an additional error on top of the chip-internal INL and DNL errors (see 6.5). For example, when using a multi-pole magnet with 1.2mm pole length instead of 1.0mm, the AS5311 will provide 1024 incremental steps or 4096 absolute positions over 2.4mm, but with an additional linearity error of up to 50µm. The curvature of ring magnets may cause linearity errors as well due to the fact that the Hall array on the chip is a straight line while the poles on the multi-pole ring are curved. These errors decrease with increasing ring diameter. It is therefore recommended to keep the ring diameter measured at the location of the Hall array at 20mm or higher. www.austriamicrosystems.com Revision 1.04 16 - 24 AS5311 Data Sheet 10.2 Position of the Index Pulse An index pulse is generated when the North and South poles are placed over the Hall array as shown in Figure 14. The incremental output count increases when the magnet is moving to the left, facing the chip with pin#1 at the lower left corner (see Figure 14, top drawing). At the same time, the absolute position value increases. Likewise, the position value decreases when the magnet is moved in the opposite direction. 10.3 Mounting the Magnet 10.3.1 Vertical Distance As a rule of thumb, the gap between chip and magnet should be ½ of the pole length, that is Z=0.5mm for the 1.0mm pole length of the AS5311 magnets. However, the gap also depends on the strength of the magnet. Typical gaps for AS5311 magnets range from 0.3 to 0.6mm (see 6.4). The AS5311 automatically adjusts for fluctuating magnet strength by using an automatic gain control (AGC). The vertical distance should be set such that the AS5311 is in the “green” range. See 7.5 for more details. 10.3.2 Alignment of Multi-pole Magnet and IC When aligning the magnet strip or ring to the AS5311, the centerline of the magnet strip should be placed exactly over the Hall array. A lateral displacement in Y-direction (across the width of the magnet) is acceptable as long as it is within the active area of the magnet. See Figure 14 for the position of the Hall array relative to Pin #1. Note: the active area in width is the area in which the magnetic field strength across the width of the magnet is constant with reference to the centerline of the magnet (see Figure 13 ). 10.3.3 Lateral stroke of Multi-pole Strip Magnets The lateral movement range (stroke) is limited by the area at which all Hall sensors of the IC are covered by the magnet in either direction. The Hall array on the AS5311 has a length of 2.0mm, hence the total stroke is maximum lateral Stroke = Length of active area – length of Hall array Note: active area in length is defined as the area containing poles with the specified 1.0mm pole length. Shorter poles at either edge of the magnet must be excluded from the active area (see Figure 13). Bpk Bpk Figure 13. Active Area of Strip Magnet Active Area Active area (length) Active area (width) B N S 2mm www.austriamicrosystems.com N S N S N S N S recommended scanning path strip length Revision 1.04 17 - 24 AS5311 Data Sheet Figure 14. Alignment of Magnet Strip with AS5311 Sensor IC position value increases leftmost magnet position Die C/L S N S N S N S N S 3.0475±0.235 N AS5311 Package Outline 1.00 position value decreases rightmost magnet position S 2.576±0.235 3.200±0.235 Die C/L N S N S N S N S N 1.00 3.0475±0.235 vertical airgap magnet strip carrier see text 1.00 ± 0.1 www.austriamicrosystems.com Revision 1.04 Note: all dimensions are in mm 18 - 24 AS5311 Data Sheet 11 Measurement Data Example Figure 15 shows typical test results of the accuracy obtained by a commercially available multi-pole magnetic strip. The graph shows the accuracy over a stroke of 8mm at two different vertical gaps, 0.2mm and 0.4mm. As displayed, the accuracy is virtually identical (about +/- 10µm) for both airgaps due to the automatic gain control of the AS5311 which compensates for airgap changes. The accuracy depends greatly on the length and strength of each pole and hence from the precision of the tool used for magnetization as well as the homogeneity of the magnet material. As the error curve in the example below does not show a repetitive pattern for each pole pair (each 2.0mm), this is most likely an indication that the pole lengths of this particular sample do not exactly match. While the first pole pair (0...2mm) shows the greatest nonlinearities, the second pole (2…4mm) is very precise, etc… Error [µm] Figure 15. Sample Test Results of INL at Different Airgaps 25 20 15 10 5 0 -5 -10 -15 -20 -25 INL MS10-10 z= 200µ z= 400µ 0 1000 2000 3000 4000 5000 6000 7000 8000 X [µm] Note: The magnet sample used in Figure 15 is a 10-pole plastic bonded ferrite magnet as shown in Figure 13. The corresponding magnet datasheet (MS10-10) is available for download from the austriamicrosystems website, magnet samples can be ordered from the austriamicrosystems online web shop. www.austriamicrosystems.com Revision 1.04 19 - 24 AS5311 Data Sheet 12 AS5311 Off-axis Rotary Applications The AS5311 can also be used as an off-axis rotary encoder, as shown in Figure 3. In such applications, the multi-pole magnetic strip is replaced by a multi-pole magnetic ring. The ring can have radial or axial magnetization. Figure 16. Angular Resolution and Maximum Speed versus Ring Diameter In off-axis rotary applications, very high angular resolutions are possible with the AS5311. The number of steps per revolution increases linearly with ring diameter. Due to the increasing number of pulses per revolution, the maximum speed decreases with increasing ring diameter. AS5311 off-axis rotary resolution & speed 160000 700 resolution speed rpm 140000 600 500 100000 400 80000 300 60000 max. speed [rpm] resolution [steps / rev] 120000 Example: a magnetic ring with 41.7mm diameter has a resolution of 65536 steps per revolution (16-bit) and a maximum speed of 305 rpm 200 40000 100 20000 0 0 20 40 60 80 100 ring diameter [mm] Res [bit] Steps / Rev. Ring Diameter [mm] Max Speed [rpm] 15 32768 20.9 609 16 65536 41.7 305 17 131072 83.4 152 The number of incremental steps per revolution can be calculated as: incremental _ steps = 1024 * nbr _ polepairs incremental _ steps = 1024 * d * π 2 Note that the circumference (d*π) must be a multiple of one polepair = 2mm, hence the diameter of the magnet ring may need to be adjusted accordingly: d= nbr _ polepairs * 2mm π The maximum rotational speed can be calculated as: max_ rot _ speed = max_ lin _ speed * 60 39000 = d *π d *π where nbr_polepairs d = the number of pole pairs at the magnet ring = diameter of the ring in mm; the diameter is taken at the locus of the Hall elements underneath the magnet max_rot_speed = maximum rotational speed in revolutions per minute rpm : max_lin_speed = maximum linear speed in mm/sec (=650 mm/s for AS5311) Note: further examples are shown in the “Magnet Selection Guide”, available for download from the austriamicrosystems website http://www.austriamicrosystems.com/eng/Products/Magnetic-Encoders/Linear-Encoders www.austriamicrosystems.com Revision 1.04 20 - 24 AS5311 Data Sheet 13 Package Drawings and Marking 20 Lead Thin Shrink Small Outline Package – TSSOP20 Figure 17. AS5311 Package Dimensions and Hall Array Location 0.2299±0.100 Die C/L 2.576±0.235 3.200±0.235 0.2341±0.100 Package Outline 0.7701±0.150 3.0475±0.235 www.austriamicrosystems.com Revision 1.04 21 - 24 AS5311 Data Sheet Dimensions Marking: AYWWIZZ mm inch Symbol Min Typ Max Min Typ Max A - - 1.10 - - 0.043 A1 0.05 - 0.15 0.002 - 0.006 A2 0.85 0.90 0.95 0.033 0.035 0.037 b 0.19 - 0.30 0.007 - 0.012 c 0.09 - 0.20 0.004 - 0.008 D 6.40 6.50 6.60 E 6.20 6.40 6.60 0.244 0.252 0.260 E1 4.30 4.40 4.50 0.169 0.173 0.177 e 0.65 .0256 K 0° - 8° L 0.50 0.60 0.75 0° 0.019 - JEDEC Package Outline Standard: MO – 153 Thermal Resistance R th(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 8° 0.024 A: Pb-Free Identifier Y: Last Digit of Manufacturing Year WW: Manufacturing Week I: Plant Identifier ZZ: Traceability Code 0.030 14 Ordering Information Delivery: Tape and Reel: 1 reel = 1000 devices 1 reel = 4500 devices Tubes: 1 box = 100 tubes à 74 devices Order # AS5311ASSU Order # AS5311ASST for delivery in tubes for delivery in tape and reel 15 Recommended PCB Footprint Recommended Footprint Data www.austriamicrosystems.com A mm 7.00 inch 0.276 B 5.00 0.197 C 0.38 0.015 D 0.65 0.026 E 6.23 0.245 Revision 1.04 22 - 24 AS5311 Data Sheet 16 Revision History Revision Date Owner Description 1.01 26-Jun-09 jja, jlu 1.02 09-Apr-10 agt Delivery information updated 1.03 24-Sep-10 agt Fig.9 updated 1.04 14-March-11 mub Table 4. Parity bit change 1…17 Recommended footprint data updated IC Marking Fig. 17 17 Copyrights Copyright © 2010, austriamicrosystems AG, Schloss Premstaetten, 8141 Unterpremstaetten, Austria – Europe. Trademarks Registered ®. All rights reserved. The material herein may not be reproduced, adapted, merged, translated, stored, or used without the prior written consent of the copyright owner. All products and companies mentioned are trademarks or registered trademarks of their respective companies. 18 Disclaimer Devices sold by austriamicrosystems AG are covered by the warranty and patent indemnification provisions appearing in its Term of Sale. austriamicrosystems AG makes no warranty, express, statutory, implied, or by description regarding the information set forth herein or regarding the freedom of the described devices from patent infringement. austriamicrosystems AG reserves the right to change specifications and prices at any time and without notice. Therefore, prior to designing this product into a system, it is necessary to check with austriamicrosystems AG for current information. This product is intended for use in normal commercial applications. Applications requiring extended temperature range, unusual environmental requirements, or high reliability applications, such as military, medical life-support or lifesustaining equipment are specifically not recommended without additional processing by austriamicrosystems AG for each application. The information furnished here by austriamicrosystems AG is believed to be correct and accurate. However, austriamicrosystems AG shall not be liable to recipient or any third party for any damages, including but not limited to personal injury, property damage, loss of profits, loss of use, interruption of business or indirect, special, incidental or consequential damages, of any kind, in connection with or arising out of the furnishing, performance or use of the technical data herein. No obligation or liability to recipient or any third party shall arise or flow out of austriamicrosystems AG rendering of technical or other services. Contact Information Headquarters austriamicrosystems AG A-8141 Schloss Premstaetten, Austria Tel: +43 (0) 3136 500 0 Fax: +43 (0) 3136 525 01 www.austriamicrosystems.com Revision 1.04 23 - 24 AS5311 Data Sheet For Sales Offices, Distributors and Representatives, please visit: http://www.austriamicrosystems.com/contact www.austriamicrosystems.com Revision 1.04 24 - 24