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| ATS625LSG True Zero-Speed Low-Jitter High Accuracy Gear Tooth Sensor Features and Benefits Highly repeatable over operating temperature range Tight timing accuracy over operating temperature range True zero-speed operation Air-gap-independent switchpoints Vibration immunity Large operating air gaps Defined power-on state Wide operating voltage range Digital output representing target profile Single-chip sensing IC for high reliability Description The ATS625 true zero-speed gear tooth sensor is an optimized Hall IC and magnet configuration packaged in a molded module that provides a manufacturer-friendly solution for digital gear tooth sensing applications. The sensor assembly consists of an over-molded package that holds together a samarium cobalt magnet, a pole piece concentrator, and a true zero-speed Hall IC that has been optimized to the magnetic circuit. This small package can be easily assembled and used in conjunction with gears of various shapes and sizes. The sensor incorporates a dual-element Hall IC that switches in response to differential magnetic signals created by a ferrous target. Digital processing of the analog signal provides zerospeed performance independent of air gap as well as dynamic adaptation of device performance to the typical operating conditions found in automotive applications (reduced vibration sensitivity). High-resolution peak detecting DACs are used to set the adaptive switching thresholds of the device. Switchpoint hysteresis reduces the negative effects of any anomalies in the magnetic signal associated with the targets used in many automotive applications. This sensor system is optimized Continued on the next page... Package: 4 pin SIP (suffix SG) Continued on the next page... Not to scale Functional Block Diagram V+ VCC Voltage Regulator Automatic Gain Control 0.1 F CBYPASS Hall Amp PDAC VPROC PPeak PThresh Reference Generator Threshold Comparator Threshold Logic NThresh NDAC NPeak Current Limit GND (Recommended) Output Transistor VOUT AUX ATS625LSG-DS, Rev. 2 ATS625LSG Features and Benefits (continued) Small mechanical size Optimized Hall IC magnetic system Fast start-up AGC and reference adjust circuit Undervoltage lockout True Zero-Speed Low-Jitter High Accuracy Gear Tooth Sensor Description (continued) for crank applications that utilize targets that possess signature regions. TheATS625 is provided in a 4-pin SIP. The Pb (lead) free option, available by special request, has a 100% matte tin plated leadframe. Selection Guide Part Number ATS625LSGTN-T3 1Pb-based Pb-free1 Yes Packing2 Tape and Reel 13-in. 800 pcs./reel variants are being phased out of the product line. Certain variants cited in this footnote are in production but have been determined to be NOT FOR NEW DESIGN. This classification indicates that sale of this device is currently restricted to existing customer applications. The device should not be purchased for new design applications because obsolescence in the near future is probable. Samples are no longer available. Status change: May 1, 2006. These variants include: ATS625LSGTN 2Contact Allegro for additional packing options. 3Some restrictions may apply to certain types of sales. Contact Allegro for details. Absolute Maximum Ratings Characteristic Supply Voltage Reverse-Supply Voltage Reverse-Supply Current Reverse-Output Voltage Output Sink Current Operating Ambient Temperature Maximum Junction Temperature Storage Temperature Symbol VCC VRCC IRCC VROUT IOUT TA TJ(max) Tstg Range L Notes See Power Derating section Rating 26.5 -18 50 -0.5 10 -40 to 150 165 -65 to 170 Units V V mA V mA C C C Pin-out Diagram Terminal List Name VCC VOUT AUX GND Description Connects power supply to chip Output from circuit For Allegro use only Ground Number 1 2 3 4 1 2 3 4 Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 2 ATS625LSG True Zero-Speed Low-Jitter High Accuracy Gear Tooth Sensor Operating Characteristics Valid at TA = -40C to 150C, TJ TJ(max), over full range of AG, unless otherwise noted; typical operating parameters: VCC = 12 V and TA = 25C Characteristic ELECTRICAL CHARACTERISTICS Supply Voltage Undervoltage Lockout Reverse Supply Current Supply Zener Clamp Voltage1 Supply Zener Current2 Supply Current POWER-ON CHARACTERISTICS Power-On State Power-On Time OUTPUT STAGE Low Output Voltage Output Current Limit Output Leakage Current Output Rise Time Output Fall Time SWITCHPOINT CHARACTERISTICS Speed Bandwidth Operate Point Release Point CALIBRATION Initial Calibration3 Calibration Update CalPO Cal Start-up Running mode operation - 1 continuous 6 edges - S BW BOP BRP Reference target 60+2 Corresponds to switching frequency - 3 dB % of peak-to-peak signal, AG < AGmax; BIN transitioning from LOW to HIGH % of peak-to-peak signal, AG < AGmax; BIN transitioning from HIGH to LOW 0 - - - - 20 60 40 12000 - - - rpm kHz % % VOUT(SAT) ISINK = 20 mA, Output = ON IOUT(LIM) IOUT(OFF) tr tf VOUT = 12 V, TJ < TJmax Output = OFF, VOUT = 24 V RL = 500 , CL = 10 pF RL = 500 , CL = 10 pF - 25 - - - 200 45 - 1.0 0.6 450 70 10 2 2 mV mA A s s SPO tPO Gear Speed < 100 RPM; VCC > VCC min - - High - - 200 V s VCC VCCUV IRCC VZ IZ ICC VCC = -18 V ICC = 17 mA VS = 28 V Output OFF Output ON Operating; TJ < TJmax 4.0 - - 28 - - - - - - - - 8.5 8.5 24 < VCC(min) -10 - 17 14 14 V V mA V mA mA mA Symbol Test Conditions Min. Typ. Max. Units Continued on the next page... Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 3 ATS625LSG True Zero-Speed Low-Jitter High Accuracy Gear Tooth Sensor Operating Characteristics, continued Valid at TA = -40C to 150C, TJ TJ(max), over full range of AG, unless otherwise noted; typical operating parameters: VCC = 12 V and TA = 25C Characteristic Symbol Test Conditions Min. Typ. Max. Units OPERATING CHARACTERISTICS with 60+2 reference target Operational Air Gap Relative Timing Accuracy, Sequential Mechanical Rising Edges Relative Timing Accuracy, Sequential Mechanical Falling Edges Relative Timing Accuracy, Signature Mechanical Rising Edge4 Relative Timing Accuracy, Signature Mechanical Falling Edge5 Relative Repeatability, Sequential Rising and Falling Edges6 Operating Signal7 1 AG ERRRR ERRFF ERRSIGR ERRSIGF TE BIN Measured from sensor branded face to target tooth Relative to measurement taken at AG = 1.5 mm Relative to measurement taken at AG = 1.5 mm Relative to measurement taken at AG = 1.5 mm Relative to measurement taken at AG = 1.5 mm 360 Repeatability, 1000 edges; peak-peak sinusoidal signal with BPEAK BIN(min) and 6 period AG(min) < AG < AG(max) 0.5 - - - - - 60 - - - - - - - 2.5 0.4 0.4 0.4 1.5 0.08 - mm deg. deg. deg. deg. deg. G Test condition is ICC(max) + 3 mA. 2 Upper limit is I CC(max) + 3 mA. 3 Power-on speed 200 rpm. Refer to the Sensor Description section for information on start-up behavior. 4 Detection accuracy of the update algorithm for the first rising mechanical edge following a signature region can be adversely affected by the magnetic bias of the signature region. Please consult with Allegro field applications engineering for aid with assessment of specific target geometries. 5 Detection accuracy of the update algorithm for the falling edge of the signature region is highly dependent upon specific target geometry. Please consult with Allegro field applications engineering for aid with assessment of specific target geometries. 6 The repeatability specification is based on statistical evaluation of a sample population. 7 Peak-to-peak magnetic flux strength required at Hall elements for complying with operational characteristics. Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 4 ATS625LSG True Zero-Speed Low-Jitter High Accuracy Gear Tooth Sensor Reference Target (Gear) Information REFERENCE TARGET 60+2 Characteristics Outside Diameter Face Width Circular Tooth Length Signature Region Circular Tooth Length Circular Valley Length Tooth Whole Depth Material Symbol Do F t Test Conditions Outside diameter of target Breadth of tooth, with respect to sensor Length of tooth, with respect to sensor; measured at Do Length of signature tooth, with respect to sensor; measured at Do Length of valley, with respect to sensor; measured at Do Low Carbon Steel Typ. 120 6 3 Units mm mm mm Symbol Key Branded Face of Sensor tV ODO tSIG tv ht 15 mm 3 3 - mm mm - Signature Region Pin 4 Pin 1 Branded Face of Sensor Reference Target 60+2 Figure 1. Configuration with Radial-Tooth Reference Target For the generation of adequate magnetic field levels, the following recommendations should be followed in the design and specification of targets: * 2 mm < tooth width, t < 4 mm * Valley width, tv > 2 mm * Valley depth, ht > 2 mm * Tooth thickness, F 3 mm * Target material must be low carbon steel Although these parameters apply to targets of traditional geometry (radially oriented teeth with radial sensing, shown in figure 1), they also can be applied in applications using stamped targets (an aperture or rim gap punched out of the target material) and axial sensing. For stamped geometries with axial sensing, the valley depth, ht, is intrinsically infinite, so the criteria for tooth width, t, valley width, tv, tooth material thickness, F, and material specification need only be considered for reference. For example, F can now be < 3 mm. 5 t,t F ht Air Gap Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com SI G ATS625LSG True Zero-Speed Low-Jitter High Accuracy Gear Tooth Sensor Characteristic Data: Electrical ICC(ON) Versus VCC 14 13 12 TA (C) -40 0 25 85 150 14 13 12 ICC(ON) Versus TA Vcc = 26.5V Vcc = 20V Vcc = 12V Vcc = 4V VCC (V) 26.5 20.0 12.0 4.0 11 10 9 8 7 6 5 0 5 10 15 20 25 30 Current (mA) Current (mA) 11 10 9 8 7 6 5 -50 -25 0 25 50 75 100 125 150 175 Voltage (V) Temperature (C) ICC(OFF) Versus VCC 14 13 12 TA (C) -40 0 25 85 150 14 13 12 ICC(OFF) Versus TA Vcc = 24V Vcc = 20V Vcc = 12V Vcc = 4V VCC (V) 24.0 20.0 12.0 4.0 Current (mA) Current (mA) 11 10 9 8 7 6 5 0 5 10 15 20 25 30 11 10 9 8 7 6 5 -50 -25 0 25 50 75 100 125 150 175 Voltage (V) Temperature (C) IOUT(OFF) Versus TA 10 8 6 400 350 300 VOUT (V) 26.5 20.0 12.0 4.0 250 200 150 100 50 0 -25 0 25 50 75 100 125 150 175 -50 -25 0 VOUT(SAT) Versus TA Current (uA) 2 0 -2 -4 -6 -8 -10 -50 Voltage (mV) 4 IOUT (mA) 25 20 15 10 5 25 50 75 100 125 150 175 Temperature (C) Temperature (C) Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 6 ATS625LSG True Zero-Speed Low-Jitter High Accuracy Gear Tooth Sensor Characteristic Data: Relative Timing Accuracy Relative Timing Accuracy Versus Speed Signature Tooth Rising Edge 0.5 mm Air Gap 1.5 Relative Timing Accuracy Versus Ambient Signature Tooth Rising Edge 0.5 mm Air Gap 1.5 1.0 TA (C) Edge Position () 1.0 Edge Position () S (rpm) 0.5 0.0 -0.5 -1.0 -1.5 -50 0 50 100 150 200 50 100 500 1000 1500 2000 0.5 0.0 -0.5 -1.0 -1.5 0 -40 0 25 85 150 500 1000 1500 2000 2500 Target Speed, S (rpm) Temperature, TA (C) Relative Timing Accuracy Versus Speed Signature Tooth Falling Edge 0.5 mm Air Gap 1.5 Relative Timing Accuracy Versus Ambient Signature Tooth Falling Edge 0.5 mm Air Gap 1.5 1.0 TA (C) -40 0 25 85 150 Edge Position () Edge Position () 1.0 0.5 0.0 -0.5 -1.0 -1.5 0 500 1000 1500 2000 2500 S (rpm) 0.5 0.0 -0.5 -1.0 -1.5 -50 50 100 500 1000 1500 2000 0 Target Speed, S (rpm) 50 100 150 Temperature, TA (C) 200 Relative Timing Accuracy Versus Speed Rising Edge Following Signature Tooth 0.5 mm Air Gap 1.5 Relative Timing Accuracy Versus Ambient Rising Edge Following Signature Tooth 0.5 mm Air Gap 1.5 TA (C) Edge Position () Edge Position () 1.0 0.5 0.0 -0.5 -1.0 -1.5 0 500 1000 1500 2000 2500 -40 0 25 85 150 1.0 S (rpm) 0.5 0.0 -0.5 -1.0 -1.5 -50 50 100 500 1000 1500 2000 0 50 100 150 200 Target Speed, S (rpm) Temperature, TA (C) Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 7 ATS625LSG True Zero-Speed Low-Jitter High Accuracy Gear Tooth Sensor Relative Timing Accuracy Versus Speed Signature Tooth Rising Edge 2.5 mm Air Gap 1.5 Relative Timing Accuracy Versus Ambient Signature Tooth Rising Edge 2.5 mm Air Gap 1.5 1.0 TA (C) Edge Position () 1.0 Edge Position () S (rpm) 0.5 0.0 -0.5 -1.0 -1.5 -50 0 50 100 150 200 50 100 500 1000 1500 2000 0.5 0.0 -0.5 -1.0 -1.5 0 -40 0 25 85 150 500 1000 1500 2000 2500 Target Speed, S (rpm) Temperature, TA (C) Relative Timing Accuracy Versus Speed Signature Tooth Falling Edge 2.5 mm Air Gap 1.5 Relative Timing Accuracy Versus Ambient Signature Tooth Falling Edge 2.5 mm Air Gap 1.5 1.0 TA (C) -40 0 25 85 150 Edge Position () Edge Position () 1.0 0.5 0.0 -0.5 -1.0 -1.5 0 500 1000 1500 2000 2500 S (rpm) 0.5 0.0 -0.5 -1.0 -1.5 -50 50 100 500 1000 1500 2000 0 Target Speed, S (rpm) 50 100 150 Temperature, TA (C) 200 Relative Timing Accuracy Versus Speed Rising Edge Following Signature Tooth 2.5 mm Air Gap 1.5 Relative Timing Accuracy Versus Ambient Rising Edge Following Signature Tooth 2.5 mm Air Gap 1.5 TA (C) Edge Position () Edge Position () 1.0 0.5 0.0 -0.5 -1.0 -1.5 0 500 1000 1500 2000 2500 -40 0 25 85 150 1.0 S (rpm) 0.5 0.0 -0.5 -1.0 -1.5 -50 50 100 500 1000 1500 2000 0 50 100 150 200 Target Speed, S (rpm) Temperature, TA (C) Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 8 ATS625LSG True Zero-Speed Low-Jitter High Accuracy Gear Tooth Sensor Relative Timing Accuracy Versus Air Gap Signature Tooth Falling Edge TA = -40, 0, 25, 85, 150 (C) Signature Tooth Rising Edge Relative Timing Accuracy Versus Air Gap TA = -40, 0, 25, 85, 150 (C) S = 50, 100, 500, 1000, 1500, 2000 (rpm) S = 50, 100, 500, 1000, 1500, 2000 (rpm) 2.0 1.5 1.0 0.5 0.0 -0.5 -1.0 -1.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 Air Gap (mm) 2.0 1.5 1.0 0.5 0.0 -0.5 -1.0 -1.5 0.0 0.5 1.0 1.5 2.0 Air Gap (mm) 2.5 3.0 Edge Position () Relative Timing Accuracy Versus Air Gap Rising Edge Following Signature Tooth TA = -40, 0, 25, 85, 150 (C) S = 50, 100, 500, 1000, 1500, 2000 (rpm) 2.0 1.5 1.0 0.5 0.0 -0.5 -1.0 -1.5 0 0.5 1.0 1.5 Air Gap (mm) Edge Position () Edge Position () 2.0 2.5 3.0 Characteristic Data: Repeatability 360 Repeatability Versus Air Gap Sequential Tooth Falling Edge S = 1000 rpm 0.25 TA (C) Repeatabilty () 0.20 0.15 0.10 0.05 0 0 1.0 -40 25 150 2.0 3.0 4.0 Air Gap (mm) Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 9 ATS625LSG True Zero-Speed Low-Jitter High Accuracy Gear Tooth Sensor Sensor Description Assembly Description The ATS625LSG true zero-speed gear tooth sensor is a combined Hall IC-magnet configuration that is fully optimized to provide digital detection of gear tooth edges. This sensor is integrally molded into a plastic body that has been optimized for size, ease of assembly, and manufacturability. High operating temperature materials are used in all aspects of construction. Sensing Technology The gear tooth sensor contains a single-chip differential Hall effect sensor IC, a 4-pin leadframe, a samarium cobalt magnet, and a flat ferrous pole piece. The Hall IC consists of two Hall elements spaced 2.2 mm apart, and each independently measures the magnetic gradient created by the passing of a ferrous object. This is illustrated in figures 2 and 3. The differential output of the two elements is converted to a digital signal that is processed to provide the digital output. Switching Description After proper power is applied to the component, the sensor is then capable of providing digital information that is representative of the profile of a rotating gear, as illustrated in figure 4. No additional optimization is needed and minimal processing circuitry is required. This ease of use reduces design time and incremental assembly costs for most applications. Target (Gear) Element Pitch Hall Element 2 South Pole Hall Element 1 Hall IC Pole Piece (Concentrator) Back-biasing Magnet North Pole (Pin n >1 Side) Plastic (Pin 1 Side) Figure 3. This left-to-right (pin 1 to pin 4) direction of target rotation results in a high output signal when a tooth of the target gear is centered over the face of the sensor. A right-to-left (pin 4 to pin 1) rotation inverts the output signal polarity. Rotating Target Branded Face of Sensor Dual-Element Hall Effect Device 1 4 Figure 2. Device Cross Section. Relative motion of the target is detected by the dual Hall elements mounted on the Hall IC. This view is from the side opposite the pins. Target Mechanical Profile Signature Tooth B+ BIN Target Magnetic Profile Sensor Output Switch State Sensor Output Electrical Profile Target Motion from Pin 1 to Pin 4 Sensor Output Electrical Profile Target Motion from Pin 4 to Pin 1 V+ VOUT On Off On Off On Off On Off On Off On Off On Off On Off V+ VOUT Figure 4. The magnetic profile reflects the geometry of the target, allowing the device to present an accurate digital output response. Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 10 ATS625LSG True Zero-Speed Low-Jitter High Accuracy Gear Tooth Sensor Undervoltage Lockout When the supply voltage falls below the undervoltage lockout level, VCCUV, the device switches to the OFF state. The device remains in that state until the voltage level is restored to to the VCC operating range. Changes in the target magnetic profile have no effect until voltage is restored. This prevents false signals caused by undervoltage conditions from propagating to the output of the sensor. Power Supply Protection The device contains an on-chip regulator and can operate over a wide range of supply voltage levels. For applications using an unregulated power supply, transient protection must be added externally. For applications using a regulated supply line, EMI and RFI protection may still be required. The circuit shown in figure 5 is the basic configuration required for proper device operation. Contact Allegro field applications engineering for information on the circuitry required for compliance to various EMC specifications. Internal Electronics The ATS625LSG contains a self-calibrating Hall effect IC that possesses two Hall elements, a temperature compensated amplifier and offset cancellation circuitry. The IC also contains a voltage regulator that provides supply noise rejection over the operating voltage range. The Hall transducers and the electronics are integrated on the same silicon substrate by a proprietary BiCMOS process. Changes in temperature do not greatly affect this device due to the stable amplifier design and the offset rejection circuitry. VS 1 VCC CBYPASS 0.1 F 3 ATS625 AUX VOUT 2 Sensor Output RPU GND 4 Figure 5. Power Supply Protection Typical Circuit Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 11 ATS625LSG True Zero-Speed Low-Jitter High Accuracy Gear Tooth Sensor Sensor Operation Description the, target feature (tooth, rising edge, falling edge, or valley) that is centered on the device at power-on, and fact that the sensor powers-on in the OFF state,with VOUT high, regardless of the eventual direction of target rotation. The interaction of these factors results in a number of possible power-on scenarios. These are diagrammed in figure 6. In all start-up scenarios, the correct number of output edges is provided, but the accuracy of the first two edges may be compromised. Target Motion Relative to Sensor Sensor Pin 1 Side Power-On State At power-on, the device is guaranteed to initialize in the OFF state, with VOUT high. First Edge Detection The device uses the first two mechanical edges to synchronize with the target features (tooth or valley) and direction of rotation of the target. The device is synchonized by the third edge. The actual behavior is affected by: target rotation direction relative to Sensor Pin 4 Side Target Mechanical Profile Target Magnetic Profile Sensor Output, VOUT (Start-up over valley) (A) Target relative movement as shown in figure 3. Output signal is high over the tooth. (Start-up over rising edge) (Start-up over tooth) (Start-up over falling edge) Sensor start-up location Sensor Pin 1 Side Sensor Pin 4 Side Target Motion Relative to Sensor Target Mechanical Profile Target Magnetic Profile (B) Target relative movement opposite that shown in figure 3. Output signal is low over the tooth. Sensor Output, VOUT (Start-up over valley) (Start-up over rising edge) (Start-up over tooth) (Start-up over falling edge) Sensor start-up location Figure 6. Start-up Position And Relative Motion Effects on First Device Output Switching. Panel A shows the effects when the target is moving from pin 1 toward pin 4 of the device; VOUT goes high at the approach of a tooth. When the target is moving in the opposite direction, as in panel B, the polarity of the device output inverts; VOUT goes low at the approach of a tooth. Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 12 ATS625LSG True Zero-Speed Low-Jitter High Accuracy Gear Tooth Sensor AGC (Automatic Gain Control) The AGC feature is implemented by a unique patented selfcalibrating circuitry. After each power-on, the device measures the peak-to-peak magnetic signal. The gain of the sensor is then adjusted, keeping the internal signal amplitude constant over the air gap range of the device, AG. This feature ensures that operational characteristics are isolated from the effects of changes in AG. The effect of AGC is shown in figure 7. Differential Electrical Signal versus Target Rotation at Various Air Gaps, Without AGC 1000 800 AG: 0.25 mm 0.50 mm 1.00 mm 1.50 mm 2.00 mm Differential Electrical Signal versus Target Rotation at Various Air Gaps, With AGC 1000 800 AG: 0.25 mm 0.50 mm 1.00 mm 1.50 mm 2.00 mm Differential Signal, VPROC (mV) 600 400 200 0 -200 -400 -600 -800 -1000 0 3 6 9 Differential Signal, VPROC (mV) 15 18 21 24 600 400 200 0 -200 -400 -600 -800 -1000 12 0 3 6 9 12 15 18 21 24 Target Rotation () Target Rotation () Figure 7. Effect of AGC. The left panel shows the process signal, VPROC, without AGC. The right panel shows the effect with AGC. The result is a normalized VPROC, which allows optimal performance by the rest of the circuits that reference this signal. Offset Adjustment In addition to normalizing performance over varying AG, the gain control circuitry also reduces the effect of chip, magnet, and installation offsets. This is accomplished using two DACs (D to A converters) that capture the peaks and valleys of the processed signal, VPROC, and use it as a reference for the Threshold Comparator subcircuit, which controls device switching. If induced offsets bias the absolute signal up or down, AGC and the dynamic DAC behavior work to normalize and reduce the impact of the offset on sensor performance. Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 13 ATS625LSG True Zero-Speed Low-Jitter High Accuracy Gear Tooth Sensor ing from the previous two edges. Because variations are tracked in real time, the sensor has high immunity to target run-out and retains excellent accuracy and functionality in the presence of both run-out and transient mechanical events. Figure 9 shows how the sensor uses historical data to provide the switching threshold for a given edge. SWITCHPOINTS Switchpoints in the ATS625 are a percentage of the amplitude of the signal, VPROC, after normalization with AGC. In operation, the actual switching levels are determined dynamically. Two DACs track the peaks of VPROC (see the Update subsection). The switching thresholds are established at 40% and 60% of the values held in the two DACs. The proximity of the thresholds near the 50% level ensures the most accurate and consistent switching, because it is where the slope of VPROC is steepest and least affected by air gap variation. The low hysteresis, 20%, provides high performance over various air gaps and immunity to false switching on noise, vibration, backlash, or other transient events. Figure 8 graphically demonstrates the establishment of the switching threshold levels.Because the thresholds are established dynamically as a percentage of the peak-to-peak signal, the effect of a baseline shift is minimized. As a result, the effects of offsets induced by tilted or off-center installation are minimized. UPDATE The ATS625 incorporates an algorithm that continuously monitors the system and updates the switching thresholds accordingly. The switchpoint for each edge is determined by the signal result- Dynamic BOP Threshold Determination V+ 100 VPROC (%) 60 BOP 0 Device State On Off (A) Switching Threshold Levels At Constant VPROC Level V+ 100 Dynamic BRP Threshold Determination V+ 100 60 40 BOP BRP VPROC (%) VPROC (%) BRP 40 0 0 Device State Off On Off On Device State Off On (B) Figure 8. Switchpoint Relationship to Thresholds.The device switches when VPROC passes a threshold level, BOP or BRP , while changing in the corresponding direction: increasing for a BOP switchpoint, and decreasing for a BRP switchpoint. Figure 9. Switchpoint Determination. The two previous VPROC peaks are used to determine the next threshold level: panel A, operate point, and panel B, release point. Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 14 ATS625LSG True Zero-Speed Low-Jitter High Accuracy Gear Tooth Sensor Sensor and Target Evaluation Magnetic Profile In order to establish the proper operating specification for a particular sensor and target system, a systematic evaluation of the magnetic circuit should be performed. The first step is the generation of a magnetic map of the target. By using a calibrated device, a magnetic profile of the system is made. Figure 10 is a magnetic map of the 60+2 reference target. A single curve can be derived from this map data, and be used to describe the peak-to-peak magnetic field strength versus the size of the air gap, AG. This allows determination of the minimum amount of magnetic flux density that guarantees operation of the sensor, BIN, so the system designer can determine the maximum allowable AG for the sensor and target system. Referring to figure 11, a BIN of 60 G corresponds to a maximum AG of approximately 2.5 mm. Magnetic Map, Reference Target 60+2 with ATS625 300 250 200 Differential Flux Density, BIN (G) 150 100 50 0 -50 -100 -150 -200 -250 -300 -350 -400 0 30 60 90 120 150 180 AG (mm) 0.75 1.00 1.50 2.00 2.50 3.00 Target Rotation () Air Gap Versus Magnetic Field, Reference Target 60+2 with ATS625 Peak-Peak Differential Flux Density, BIN (G) 800 700 600 500 400 300 200 100 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 AG (mm) Figure 10. Magnetic Data for the Reference Target 60+2 with ATS625. In the top panel, the Signature Region appears in the center of the plot. Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 15 ATS625LSG True Zero-Speed Low-Jitter High Accuracy Gear Tooth Sensor scope, close to the desired output edge, the speed variations that occur within a single revolution of the target are effectively nullified. Because the trigger event occurs a very short time before the measured event, little opportunity is given for measurement system jitter to impact the time-based measurements. After the data is taken on the oscilloscope, statistical analysis of the distribution is made to quantify variability and capability. Although complete repeatability results can be found in the Characteristic Data: Repeatability section, figure 11 shows the correlation between magnetic signal strength and repeatability. Because an direct relationship exists between magnetic signal strength and repeatability, optimum repeatability performance can be attained through minimizing the operating air gap and optimizing the target design. ACCURACY While the update algorithm will allow the sensor to adapt to typical air gap variations, major changes in air gap can adversely affect switching performance. When characterizing sensor performance over a significant air gap range, be sure to re-power the device at each test at different air gaps. This ensures that self-calibration occurs for each installation condition. See the Operating Characteristics table and the charts in the Characteristic Data: Relative Timing Accuracy section for performance information. REPEATABILITY Repeatability measurement methodology has been formulated to minimize the effect of test system jitter on device measurements. By triggering the measurement instrument, such as an oscillo- Target Mechanical Profile Low Resolution Encoder Oscilloscope triggers at n events after low-resolution pulse Next high-resolution encoder pulse (at target edge) High Resolution Encoder Sensor Output Electrical Profile (target movement from pin 1 to pin 4) Oscilloscope trace of 1000 sweeps for the same output edge Statistical distribution of 1000 sweeps X Figure 11. Repeatability Measurement Methodology Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 16 ATS625LSG True Zero-Speed Low-Jitter High Accuracy Gear Tooth Sensor Power Derating THERMAL CHARACTERISTICS may require derating at maximum conditions, see application information Characteristic Package Thermal Resistance Symbol RJA Test Conditions* Minimum-K PCB (single layer, single-sided, with copper limited to solder pads) Low-K PCB (single-layer, single-sided with copper limited to solder pads and 3.57 in.2 (23.03 cm2) of copper area each side) Value Units 126 84 C/W C/W *Additional information is available on the Allegro Web site. Power Derating Curve TJ(max) = 165C VCC(max) 25 30 Maximum Allowable VCC (V) 20 15 Low-K PCB (R JA = 84 C/W) Minimum-K PCB (R JA = 126 C/W) 10 5 VCC(min) 0 20 40 60 80 100 120 140 160 180 Power Dissipation Versus Ambient for Sample PCBs 1900 1800 1700 1600 1500 1400 1300 1200 1100 1000 900 800 700 600 500 400 300 200 100 0 20 40 Power Dissipation, PD (m W) K J A = PC Mi n 84 B (R imu C mJ A= KP /W 12 ) 6 CB C/ W) Lo (R w- 60 80 100 120 140 Temperature, TA (C) 160 180 Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 17 ATS625LSG True Zero-Speed Low-Jitter High Accuracy Gear Tooth Sensor The device must be operated below the maximum junction temperature of the device, TJ(max). Under certain combinations of peak conditions, reliable operation may require derating supplied power or improving the heat dissipation properties of the application. This section presents a procedure for correlating factors affecting operating TJ. (Thermal data is also available on the Allegro MicroSystems Web site.) The Package Thermal Resistance, RJA, is a figure of merit summarizing the ability of the application and the device to dissipate heat from the junction (die), through all paths to the ambient air. Its primary component is the Effective Thermal Conductivity, K, of the printed circuit board, including adjacent devices and traces. Radiation from the die through the device case, RJC, is relatively small component of RJA. Ambient air temperature, TA, and air motion are significant external factors, damped by overmolding. The effect of varying power levels (Power Dissipation, PD), can be estimated. The following formulas represent the fundamental relationships used to estimate TJ, at PD. PD = VIN x IIN T = PD x RJA TJ = TA + T (1) (2) (3) Example: Reliability for VCC at TA = 150C, package SG, using minimum-K PCB. Observe the worst-case ratings for the device, specifically: RJA = 126C/W, TJ(max) = 165C, VCC(max) = 26.5 V, and ICC(max) = 8 mA. Note that ICC(max) at TA = 150C is lower than the ICC(max) at TA = 25C given in the Operating Characteristics table. Calculate the maximum allowable power level, PD(max). First, invert equation 3: Tmax = TJ(max) - TA = 165 C - 150 C = 15 C This provides the allowable increase to TJ resulting from internal power dissipation. Then, invert equation 2: PD(max) = Tmax / RJA = 15C / 126 C/W = 119 mW Finally, invert equation 1 with respect to voltage: VCC(est) = PD(max) / ICC(max) = 119 mW / 8 mA = 14.9 V The result indicates that, at TA, the application and device can dissipate adequate amounts of heat at voltages VCC(est). Compare VCC(est) to VCC(max). If VCC(est) VCC(max), then reliable operation between VCC(est) and VCC(max) requires enhanced RJA. If VCC(est) VCC(max), then operation between VCC(est) and VCC(max) is reliable under these conditions. For example, given common conditions such as: TA= 25C, VIN = 12 V, IIN = 4 mA, and RJA = 140 C/W, then: PD = VIN x IIN = 12 V x 4 mA = 48 mW T = PD x RJA = 48 mW x 140 C/W = 7C TJ = TA + T = 25C + 7C = 32C A worst-case estimate, PD(max), represents the maximum allowable power level, without exceeding TJ(max), at a selected RJA and TA. Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 18 ATS625LSG True Zero-Speed Low-Jitter High Accuracy Gear Tooth Sensor Sensor Evaluation: EMC Characterization Only Test Name* Reference Specification ESD - Human Body Model AEC-Q100-002 ESD - Machine Model AEC-Q100-003 Conducted Transients ISO 7637-1 Direct RF Injection ISO 11452-7 Bulk Current Injection ISO 11452-4 TEM Cell ISO 11452-3 *Please contact Allegro MicroSystems for EMC performance Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 19 ATS625LSG True Zero-Speed Low-Jitter High Accuracy Gear Tooth Sensor Package SG, 4-Pin SIP 5.5 .217 C E 1.10 .0433 1.10 .0433 B 8.0 .315 5.8 .228 2.9 .114 E 4.7 .185 A 1.7 .067 1 2 3 4 0.38 .015 1.08 .043 0.4 .016 20.95 .825 15.3 .602 A D 0.6 .024 1.27 .050 Preliminary dimensions, for reference only Untoleranced dimensions are nominal. Dimensions in millimeters U.S. Customary dimensions (in.) in brackets, for reference only Dimensions exclusive of mold flash, burrs, and dambar protrusions Exact case and lead configuration at supplier discretion within limits shown A Dambar removal protrusion (16X) B Metallic protrusion, electrically connected to pin 4 and substrate (both sides) C Active Area Depth, 0.43 [.017] D Thermoplastic Molded Lead Bar for alignment during shipment E Hall elements (2X) Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 20 ATS625LSG True Zero-Speed Low-Jitter High Accuracy Gear Tooth Sensor The products described herein are manufactured under one or more of the following U.S. patents: 5,045,920; 5,264,783; 5,442,283; 5,389,889; 5,581,179; 5,517,112; 5,619,137; 5,621,319; 5,650,719; 5,686,894; 5,694,038; 5,729,130; 5,917,320; and other patents pending. Allegro MicroSystems, Inc. reserves the right to make, from time to time, such departures from the detail specifications as may be required to permit improvements in the performance, reliability, or manufacturability of its products. Before placing an order, the user is cautioned to verify that the information being relied upon is current. Allegro products are not authorized for use as critical components in life-support devices or systems without express written approval. The information included herein is believed to be accurate and reliable. However, Allegro MicroSystems, Inc. assumes no responsibility for its use; nor for any infringement of patents or other rights of third parties which may result from its use. Copyright (c) 2005, 2006 Allegro MicroSystems, Inc. Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 21 |
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