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| ATS643LSH Self-Calibrating, Zero-Speed Differential Gear Tooth Sensor with Continuous Update Features and Benefits Fully-optimized differential digital gear tooth sensor Single chip-IC for high reliability Internal current regulator for 2-wire operation Small mechanical size (8 mm diameter x 5.5 mm depth) Switchpoints air gap independent Digital output representing gear profile Precise duty cycle accuracy throughout temperature range Large operating air gaps <2 ms power-on time Description The ATS643 is an optimized combination of integrated circuit and magnet that provides a manufacturer-friendly solution for true zero-speed digital gear-tooth sensing in two-wire applications. The device consists of a single-shot molded plastic package that includes a samarium cobalt magnet, a pole piece, and a Hall-effect IC that has been optimized to the magnetic circuit and the automotive environment. This small package can be easily assembled and used in conjunction with a wide variety of gear shapes and sizes. The integrated circuit incorporates a dual element Hall-effect sensor with signal processing circuitry that switches in response to differential magnetic signals created by rotating ferrous targets. The device contains a sophisticated compensating circuit to eliminate magnet and system offsets immediately at power-on. Digital tracking of the analog signal is used to achieve true zero-speed operation, while also setting the device switchpoints. The resulting switchpoints are air gap independent, greatly improving output and duty cycle accuracy. The device also uses a continuous update algorithm to finetune the switchpoints while in running mode, maintaining Continued on the next page... Packages: 4 pin SIP (suffix SH) Continued on the next page... Not to scale Functional Block Diagram VCC (Pin 1) Hall AMP Offset Adjust AGC Internal Regulator PDAC ThresholdP Reference Generator and Updates ThresholdN NDAC Threshold Logic GND (Pin 4) ATS643-DS, Rev. 2 ATS643LSH Features and Benefits (continued) AGC and reference adjust circuit True zero-speed operation Undervoltage lockout Wide operating voltage range Defined power-on state Self-Calibrating, Zero-Speed Differential Gear Tooth Sensor with Continuous Update Description (continued) the device specifications even through large changes in air gap or temperature. The regulated current output is configured for two-wire operation, offering inherent diagnostic information. This device is ideal for obtaining speed and duty cycle information in gear-tooth based applications such as transmission speed sensing. Part Number ATS643LSHTN-I1-T ATS643LSHTN-I2-T 1Pb-based Pb-free1 Yes Yes Packing2 Tape and Reel 13-in. 800 pcs./reel Tape and Reel 13-in. 800 pcs./reel ICC Typical 6.0 Low to 14.0 High mA 7.0 Low to 14.0 High mA 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: ATS643LSHTN-I1 and ATS643LSHTN-I2. 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 Operating Ambient Temperature Maximum Junction Temperature Storage Temperature Symbol VCC VRCC TA TJ(max) Tstg Range L Notes See Power Derating section Rating - -18 -40 to 150 165 -65 to 170 Units - V C C C Pin-out Diagram Terminal List Name VCC NC TEST GND Description Connects power supply to chip No connection. Float or tie to VCC For Allegro use, float or tie to GND Ground terminal Number 1 2 3 4 1234 Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 2 ATS643LSH Self-Calibrating, Zero-Speed Differential Gear Tooth Sensor with Continuous Update Symbol Test Conditions Min. Typ. Max. Units OPERATING CHARACTERISTICS using reference target 60-0, TA and VCC within specification, unless otherwise noted Characteristic ELECTRICAL CHARACTERISTICS Supply Voltage Undervoltage Lockout Supply Zener Clamp Voltage VCC VCC(UV) VZ ICC(Low) Supply Current ICC(High) Supply Current Ratio Operating; TJ < 165 C VCC 0 5 V ICC = 19 mA for ATS643-I1, and 19.8 mA for ATS643-I2; TA = 25C ATS643-I1 ATS643-I2 ATS643-I1 ATS643-I2 4.0 - 28 4.0 5.9 12.0 11.8 1.85 - 3.5 - 6 7 14.0 14.0 - 24 4.0 - 8.0 8.4 16.0 16.8 3.05 V V V mA mA mA mA - ICC(High)/ Ratio of high current to low current ICC(Low) ICC(PO) ton t < ton; dI/dt < 5 s Target gear speed < 100 rpm POWER-ON CHARACTERISTICS Power-On State Power-On Time1 OUTPUT STAGE Output Slew Rate2 Output State dI/dt VOUT RLOAD = 100 , CLOAD = 10 pF RSENSE on high side (VCC pin); ICC = ICC(High) RSENSE on low side (GND pin); ICC = ICC(High) - - - 7 Low High - - - mA/s mV mV - - High 1 - 2 mA ms Continued on the next page. Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 3 ATS643LSH Self-Calibrating, Zero-Speed Differential Gear Tooth Sensor with Continuous Update Symbol Test Conditions Min. Typ. Max. Units OPERATING CHARACTERISTICS (continued) using reference target 60-0, TA and VCC within specification, unless otherwise noted Characteristic SWITCHPOINT CHARACTERISTICS Rotation Speed Bandwidth Operate Point Release Point CALIBRATION3 Initial Calibration Period AGC Calibration Disable Start Mode Hysteresis DAC CHARACTERISTICS Dynamic Offset Cancellation Tracking Data Resolution FUNCTIONAL CHARACTERISTICS Air Gap Range4 Maximum Operable Air Gap Duty Cycle Variation Input Signal Range Minimum Operable Input Signal 1Power-On 2dI SROT BW BOP BRP Reference Target 60-0 Equivalent to f - 3dB % of peak to peak referenced from PDAC to NDAC, AG < AGMAX % of peak to peak referenced from PDAC to NDAC, AG < AGMAX Quantity of rising output (current) edges required for accurate edge detection Quantity of rising output (current) edges used for calibrating AGC 0 25 - - - 40 65 35 12,000 - - - rpm kHz % % CI Cf POHYS - - - - - 175 3 3 - Edge Edge mV - Quantity of bits available for PDAC/NDAC tracking of both positive and negative signal peaks - 60 9 - - G Bit AG AG(opmax) DC Sig Sig(opmin) DC within specification Output switching (no missed edges); DC not guaranteed Wobble < 0.5 mm, AG within specification DC within specification Output switching (no missed edges); DC not guaranteed 0.5 - - 40 30 - - - - - 2.5 2.75 10 1400 - mm mm % G G Time includes the time required to complete the internal automatic offset adjust. The DACs are then ready for peak acquisition. is the difference between 10% of ICC(Low) and 90% of ICC(High) , and dt is time period between those two points. Note: dI/dt is dependent upon the value of the bypass capacitor, if one is used. 3Continuous Update (calibration) functions continuously during Running mode operation. 4AG is dependent on the available magnetic field. The available field is dependent on target geometry and material, and should be independently characterized. The field available from the reference target is given in the reference target parameter section of the datasheet. Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 4 ATS643LSH Characteristics Outside Diameter Face Width Circular Tooth Length Circular Valley Length Tooth Whole Depth Material Symbol Do F t tv ht Self-Calibrating, Zero-Speed Differential Gear Tooth Sensor with Continuous Update 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 valley, with respect to sensor; measured at Do Low Carbon Steel Typ. 120 6 3 3 3 - Units mm mm mm mm mm - Symbol Key REFERENCE TARGET, 60-0 (60 Tooth Target) Reference Gear Magnetic Gradient Amplitude with Reference to Air Gap 1800 1600 1400 1200 1000 800 600 400 200 0 0.5 1 AG (mm) 1.5 2 2.5 Peak-to-Peak Differential B* (G) Branded Face of Sensor Reference Target 60-0 700 600 500 Reference Gear Magnetic Profile Two Tooth-to-Valley Transitions Differential B* (G) 400 300 200 100 0 -100 -200 -300 -400 -500 -600 -700 0 1 2 3 4 5 6 7 8 9 10 11 12 Gear Rotation () 2.00 mm AG 0.50 mm AG AG (mm) 0.50 0.75 1.00 1.25 1.50 1.75 2.00 *Differential B corresponds to the calculated difference in the magnetic field as sensed simultaneously at the two Hall elements in the device (BDIFF = BE1 - BE2). Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 5 ATS643LSH Self-Calibrating, Zero-Speed Differential Gear Tooth Sensor with Continuous Update Characteristic Data Data taken from 3 lots, 30 pieces/lot; I1 trim Reference Target 60-0 Duty Cycle at 1000 RPM 60 AG (mm) 3.0 2.75 2.5 2.25 2.0 1.5 1.0 0.5 Duty Cycle at 1000 RPM 60 Duty Cycle (%) 50 Duty Cycle (%) 55 55 50 TA (C) 45 45 -40 0 25 85 150 40 -50 0 50 100 150 200 40 0 0.5 1 1.5 2 2.5 3 3.5 TA (C) AG (mm) Duty Cycle (25C) 60 AG (mm) 3.0 2.75 2.5 2.25 2.0 1.5 1.0 0.5 Duty Cycle (%) 55 50 45 40 0 500 1000 1500 2000 2500 RPM Continued on the next page. Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 6 ATS643LSH Self-Calibrating, Zero-Speed Differential Gear Tooth Sensor with Continuous Update Characteristic Data (continued) Data taken from 3 lots, 30 pieces/lot; I1 trim ICC (Low) ICC(Low) VCC 9 TA (C) 8 150 85 25 0 -40 26.5 20.0 12.0 4.0 9 8 Icc (mA) 7 6 Icc (mA) 7 6 5 5 4 4 3 -50 3 0 50 100 150 200 0 5 10 15 20 25 30 TA (C) Vcc (V) I CC(High) 17 V26.5V CC 16 26.5 20V 20.0 12V 12.0 4V 4.0 I CC(High) 17 TA (C) 16 150 85 25 0 -40 Icc (mA) 14 Icc (mA) 0 50 100 150 200 15 15 14 13 13 12 12 11 -50 11 0 5 10 15 20 25 30 TA (C) Vcc (V) I+ Output current in relation to sensed magnetic flux density. Transition through BOP must precede by transition through BRP. Hysteresis of IICC Switching Due to B ICC(High) Switch to High Switch to Low ICC ICC(Low) BOP B+ BRP BHYS Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 7 ATS643LSH Self-Calibrating, Zero-Speed Differential Gear Tooth Sensor with Continuous Update THERMAL CHARACTERISTICS may require derating at maximum conditions, see application information Characteristic Package Thermal Resistance Symbol RJA Test Conditions Min. Minimum-K PCB (single-sided with copper limited to 126 solder pads) Low-K PCB (single-sided with copper limited to solder 84 pads and 3.57 in.2 (23.03 cm2) of copper area) Typ. - - Max Units - - C/W C/W 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 20 40 Power Derating Curve TJ(max) = 165C; ICC = ICC(max) Maximum Allowable VCC (V) VCC(max) Low-K PCB (RJA = 84 C/W) Minimum-K PCB (RJA = 126 C/W) VCC(min) 60 80 100 120 140 160 180 1900 1800 1700 1600 1500 1400 1300 1200 1100 1000 900 800 700 600 500 400 300 200 100 0 20 Maximum Power Dissipation, PD(max) TJ(max) = 165C; VCC = VCC(max); ICC = ICC(max) 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- 40 60 80 100 120 Temperature (C) 140 160 180 Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 8 ATS643LSH Self-Calibrating, Zero-Speed Differential Gear Tooth Sensor with Continuous Update Functional Description incremental assembly costs for most applications. Determining Output Signal Polarity. In figure 3, the top panel, labeled Mechanical Position, represents the mechanical features of the target gear and orientation to the device. The bottom panel, labeled Sensor Output Signal, displays the square waveform corresponding to the digital output signal that results from a rotating gear configured as shown in figure 2. That direction of rotation (of the gear side adjacent to the face of the sensor) is: perpendicular to the leads, across the face of the device, from the pin 1 side to the pin 4 side. This results in the sensor output switching from low, ICC(Low), to high, ICC(High), as the leading edge of a tooth (a rising mechanical edge, as detected by the sensor) passes the sensor face. In this configuration, the device output current switches to its high polarity when a tooth is the target feature nearest to the sensor. If the direction of rotation is reversed, so that the gear rotates from the pin 4 side to the pin 1 side, then the output polarity inverts. That is, the output signal goes high when a falling edge is detected, and a valley is the nearest to the sensor. Note, however, that the polarity of IOUT depends on the position of the sense resistor, RSENSE (see Operating Characteristics table). Continuous Update of Switchpoints. Switchpoints are the threshold levels of the differential internal analog signal, VPROC, at which the device changes output signal polarity. The value of Mechanical Position (Target movement pin 1 to pin 4) Element Pitch Hall Element 1 Hall IC Pole Piece (Concentrator) Back-biasing Magnet North Pole Case (Pin 1 Side) This tooth sensed earlier Sensing Technology. The ATS643 module contains a single-chip differential Hall effect sensor IC, a samarium cobalt magnet, and a flat ferrous pole piece (concentrator). As shown in figure 1, the Hall IC supports two Hall elements, which sense the magnetic profile of the ferrous gear target simultaneously, but at different points (spaced at a 2.2 mm pitch), generating a differential internal analog voltage (VPROC) that is processed for precise switching of the digital output signal. The Hall IC is self-calibrating and also possesses a temperature compensated amplifier and offset cancellation circuitry. Its voltage regulator provides supply noise rejection throughout the operating voltage range. Changes in temperature do not greatly affect this device due to the stable amplifier design and the offset rejection circuitry. The Hall transducers and signal processing electronics are integrated on the same silicon substrate, using a proprietary BiCMOS process. Target Profiling During Operation. When proper power is applied to the sensor, it is capable of providing digital information that is representative of the mechanical features of a rotating gear. The waveform diagram in figure 3 presents the automatic translation of the mechanical profile, through the magnetic profile that it induces, to the digital output signal of the ATS643. No additional optimization is needed and minimal processing circuitry is required. This ease of use reduces design time and Target (Gear) Hall Element 2 Target (Gear) This tooth sensed later Dual-Element Hall Effect Device South Pole Target Magnetic Profile +B Sensor Orientation to Target Pin 4 Side Sensor Branded Face (Pin n >1 Side) Sensor Figure 1. Relative motion of the target is detected by the dual Hall elements mounted on the Hall IC. Pin 1 Side Sensor Internal Differential Analog Signal, VPROC BOP(#1) BOP(#2) BRP(#1) +t Rotating Target Branded Face of Sensor Sensor Internal Switch State Off 1 4 On Off On +t Sensor Output Signal, IOUT Figure 2. 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 nearest the face of the sensor (see figure 3). A right-to-left (pin 4 to pin 1) rotation inverts the output signal polarity. +t Figure 3. The magnetic profile reflects the geometry of the target, allowing the ATS643 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 9 ATS643LSH Self-Calibrating, Zero-Speed Differential Gear Tooth Sensor with Continuous Update release point, BRP , the switch toggles from on to off. As shown in panel C of figure 4, threshold levels for the ATS643 switchpoints are established dynamically as function of the peak input signal levels. The ATS643 incorporates an algorithm that continuously monitors the system and updates the switching thresholds accordingly. The switchpoint for each edge is determined by the detection of the previous two edges. In this manner, variations are tracked in real time. VPROC is directly proportional to the magnetic flux density, B, induced by the target and sensed by the Hall elements. When VPROC transitions through a switchpoint from the appropriate higher or lower level, it triggers sensor switch turn-on and turnoff. As shown in figure 3, when the switch is in the off state, as VPROC rises through a certain limit, referred to as the operate point, BOP , the switch toggles from off to on. When the switch is in the on state, as VPROC falls below BOP to a certain limit, the (A) TEAG varying; cases such as eccentric mount, out-of-round region, normal operation position shift (B) Internal analog signal, VPROC, typically resulting in the sensor V+ Smaller TEAG Larger TEAG Smaller TEAG Target Target VPROC (V) Sensor Smaller TEAG Sensor Larger TEAG Hysteresis Band (Delimited by switchpoints) 0 Target Rotation () 360 (C) Referencing the internal analog signal, VPROC, to continuously update device response BHYS Switchpoint 1 2 3 4 BOP(#1) BRP(#1) BOP(#2) BRP(#2) BOP(#3) BRP(#3) BOP(#4) BRP(#4) Determinant Peak Values Pk(#1), Pk(#2) Pk(#2), Pk(#3) Pk(#3), Pk(#4) Pk(#4), Pk(#5) Pk(#5), Pk(#6) Pk(#6), Pk(#7) Pk(#7), Pk(#8) Pk(#8), Pk(#9) V+ Pk(#1) Pk(#3) Pk(#5) BOP(#2) BOP(#3) BRP(#1) Pk(#4) Pk(#2) BHYS(#1) BHYS(#2) BRP(#2) Pk(#6) Pk(#8) BHYS(#3) BRP(#3) BOP(#4) Pk(#7) Pk(#9) VPROC (V) BOP(#1) BRP(#4) BHYS(#4) t+ Figure 4. The Continuous Update algorithm allows the Allegro sensor to immediately interpret and adapt to significant variances in the magnetic field generated by the target as a result of eccentric mounting of the target, out-of-round target shape, elevation due to lubricant build-up in journal gears, and similar dynamic application problems that affect the TEAG (Total Effective Air Gap). The algorithm is used to dynamically establish and subsequently update the device switchpoints (BOP and BRP). The hysteresis, BHYS(#x), at each target feature configuration results from this recalibration, ensuring that it remains properly proportioned and centered within the peak-to-peak range of the internal analog signal, VPROC. As shown in panel A, the variance in the target position results in a change in the TEAG. This affects the sensor as a varying magnetic field, which results in proportional changes in the internal analog signal, VPROC, shown in panel B. The Continuous Update algorithm is used to establish accurate switchpoints based on the fluctuation of VPROC, as shown in panel C. Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 10 ATS643LSH Self-Calibrating, Zero-Speed Differential Gear Tooth Sensor with Continuous Update however, it allows the device to optimize for continuous update yielding adaptive sensing during Running mode. As shown in figure 5, the first three high peak signals are used to calibrate AGC. However, there is a slight variance in the duration of initialization, depending on what target feature is nearest the sensor when power-on occurs. Power-On State Operation. The ATS643 is guaranteed to power-on in the high current state, ICC(High). Initial Edge Detection. The device self-calibrates using the initial teeth sensed, and then enters Running mode. This results in reduced accuracy for a brief period (less than four teeth), Target (Gear) Sensor Position 1 2 3 4 VPROC Power-on over valley 1 Output Start Mode Hysteresis Overcome AGC Calibration Running Mode VPROC Power-on at rising edge 2 Output Start Mode Hysteresis Overcome AGC Calibration Running Mode VPROC Power-on over tooth 3 Output Start Mode Hysteresis Overcome AGC Calibration Running Mode VPROC Power-on at falling edge 4 Output Start Mode Hysteresis Overcome AGC Calibration Running Mode Figure 5. Power-on initial edge detection. This figure demonstrates four typical power-on scenarios. All of these examples assume that the target is moving relative to the sensor in the direction indicated. The length of time required to overcome Start Mode Hysteresis, as well as the combined effect of whether it is overcome in a positive or negative direction plus whether the next edge is in that same or opposite polarity, affect the point in time when AGC calibration begins. Three high peaks are always required for AGC calibration. Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 11 ATS643LSH Self-Calibrating, Zero-Speed Differential Gear Tooth Sensor with Continuous Update A typical scenario is shown in figure 6. The hysteresis, POHYS, is a minimum level of the peak-to-peak amplitude of the internal analog electrical signal, VPROC, that must be exceeded before the ATS643 starts to compute switchpoints. Start Mode Hysteresis. This feature helps to ensure optimal self-calibration by rejecting electrical noise and low-amplitude target vibration during initialization. This prevents AGC from calibrating the sensor on such spurious signals. Calibration can be performed using the actual target features. Target, Gear Sensor Position Relative to Target Target Magnetic Profile 1 2 5 Differential Signal, VPROC Start Mode Hysteresis, POHYS BOP(#1) BRP(#1) BOP(#2) 1 Output Signal, IOUT 2 3 4 5 Figure 6. Operation of Start Mode Hysteresis Position 1. At power-on, the ATS643 begins sampling VPROC. Position 2. At the point where the Start Mode Hysteresis is exceeded, the device begins to establish switching thresholds (BOP and BRP) using the Continuous Update algorithm. After this point, Start Mode Hysteresis is no longer a consideration. Note that a valid VPROC value exceeding the Start Mode Hysteresis can be generated either by a legitimate target feature or by excessive vibration. Position 3. In this example, the first switchpoint transition is through BOP . and the output transitions from high to low. If the first switchpoint transition had been through BRP (such as position 4), no output transition would occur because IOUT already would be in the high polarity. The first transition would occur at position 5 (BOP). Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 12 ATS643LSH Self-Calibrating, Zero-Speed Differential Gear Tooth Sensor with Continuous Update power-on, the device determines the peak-to-peak amplitude of the signal generated by the target. The gain of the sensor is then automatically adjusted. Figure 8 illustrates the effect of this feature. Automatic Offset Adjust (AOA). The AOA is patented circuitry that automatically cancels the effects of chip, magnet, and installation offsets. (For capability, see Dynamic Offset Cancellation, in the Operating Characteristics table.) This circuitry is continuously active, including both during power-on mode and running mode, compensating for any offset drift. Continuous operation also allows it to compensate for offsets induced by temperature variations over time. Assembly Description. The ATS643 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. Undervoltage Lockout. When the supply voltage falls below the minimum operating voltage, VCC(UV), ICC goes high and remains high regardless of the state of the magnetic gradient from the target. This lockout feature 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 VCC range. For devices that need to operate from an unregulated power supply, transient protection must be added externally. For applications using a regulated line, EMI/RFI protection may still be required. Contact Allegro Microsystems for information on the circuitry needed for compliance with various EMC specifications. Refer to figure 7 for an example of a basic application circuit. Automatic Gain Control (AGC). This feature allows the device to operate with an optimal internal electrical signal, regardless of the air gap (within the AG specification). At Ferrous Target Mechanical Profile V+ (Optional) 1 VCC Internal Differential Analog Signal Response, without AGC AGLarge 2 ATS643 3 0.01 F (Optional) AGSmall V+ Internal Differential Analog Signal Response, with AGC AGSmall AGLarge 4 100 Figure 7. Typical basic circuit for proper device operation. Figure 8. Automatic Gain Control (AGC). The AGC function corrects for variances in the air gap. Differences in the air gap cause differences in the magnetic field at the device, but AGC prevents that from affecting device performance, a shown in the lowest panel. Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 13 ATS643LSH Self-Calibrating, Zero-Speed Differential Gear Tooth Sensor with Continuous Update Power Derating Example: Reliability for VCC at TA = 150C, package L-I1, using minimum-K PCB Observe the worst-case ratings for the device, specifically: RJA = 126C/W, TJ(max) = 165C, VCC(max) = 24 V, and ICC(max) = 16 mA. 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 / 16 mA = 7 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. 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) For example, given common conditions such as: TA= 25C, VCC = 12 V, ICC = 4 mA, and RJA = 140 C/W, then: PD = VCC x ICC = 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 (VCC(max), ICC(max)), 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 14 ATS643LSH Self-Calibrating, Zero-Speed Differential Gear Tooth Sensor with Continuous Update Package SH, 4-pin SIP 5.5 .217 B 8.0 .315 5.8 .228 4.0 5.0 .244 .157 1.7 .067 1 2 3 4 A 0.38 .015 1.08 .043 1 .039 20.95 .825 13.05 .514 A 0.6 .024 D 0.6 .024 1.27 .050 Dimensions in millimeters. Untoleranced dimensions are nominal. U.S. Customary dimensions (in.) in brackets, for reference only A Dambar removal protrusion (16X) B Metallic protrusion, electrically connected to pin 4 and substrate (both sides) C Active Area Depth D Thermoplastic Molded Lead Bar for alignment during shipment Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 15 ATS643LSH Self-Calibrating, Zero-Speed Differential Gear Tooth Sensor with Continuous Update 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) 2004, 2006 Allegro MicroSystems, Inc. Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 16 |
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