ATS643LSH Self-Calibrating, Zero-Speed Differential Gear Tooth Sensor IC with Continuous Update Last Time Buy This part is in production but has been determined to be LAST TIME BUY. This classification indicates that the product is obsolete and notice has been given. Sale of this device is currently restricted to existing customer applications. The device should not be purchased for new design applications because of obsolescence in the near future. Samples are no longer available. Date of status change: May 2, 2011 Deadline for receipt of LAST TIME BUY orders: October 31, 2011 Recommended Substitutions: For existing customer transition, and for new customers or new applications, refer to the ATS685. NOTE: For detailed information on purchasing options, contact your local Allegro field applications engineer or sales representative. Allegro MicroSystems, Inc. reserves the right to make, from time to time, revisions to the anticipated product life cycle plan for a product to accommodate changes in production capabilities, alternative product availabilities, or market demand. The information included herein is believed to be accurate and reliable. However, Allegro MicroSystems, Inc. assumes no responsibility for its use; nor for any infringements of patents or other rights of third parties which may result from its use. ATS643LSH Self-Calibrating, Zero-Speed Differential Gear Tooth Sensor IC with Continuous Update Features and Benefits Description The ATS643 is an optimized combination of integrated circuit and rare-earth pellet that provides a manufacturer-friendly solution for true zero-speed digital gear-tooth sensing in twowire applications. The device consists of a single-shot molded plastic package that includes a samarium cobalt pellet, 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. Fully-optimized differential digital gear tooth sensor IC 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 AGC and reference adjust circuit Continued on the next page... Packages: 4 pin SIP (suffix SH) The integrated circuit incorporates a dual element Hall-effect IC with signal processing circuitry that switches in response to differential magnetic signals created by rotating ferromagnetic 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... Not to scale Functional Block Diagram VCC (Pin 1) Hall AMP Offset Adjust AGC Internal Regulator PDAC ThresholdP Reference Generator and Updates Threshold Logic ThresholdN NDAC ATS643-DS, Rev. 6 GND (Pin 4) Self-Calibrating, Zero-Speed Differential Gear Tooth Sensor IC with Continuous Update ATS643LSH Features and Benefits (continued) True zero-speed operation Undervoltage lockout Wide operating voltage range Defined power-on state 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 Packing* ICC Typical ATS643LSHTN-I1-T Tape and Reel 13-in. 800 pcs./reel 6.0 Low to 14.0 High mA ATS643LSHTN-I2-T Tape and Reel 13-in. 800 pcs./reel 7.0 Low to 14.0 High mA *Contact Allegro for additional packing options. Some restrictions may apply to certain types of sales. Contact Allegro for details. Absolute Maximum Ratings Characteristic Symbol Supply Voltage VCC Reverse-Supply Voltage VRCC Notes See Power Derating section Units - V -18 V -40 to 150 C Operating Ambient Temperature TA Maximum Junction Temperature TJ(max) 165 C Tstg -65 to 170 C Storage Temperature Pin-out Diagram Range L Rating Terminal List Name VCC 1 2 3 4 Description Number Connects power supply to chip 1 NC No connection. Float or tie to VCC 2 TEST For Allegro use, float or tie to GND 3 GND Ground terminal 4 Allegro MicroSystems, Inc. 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 2 Self-Calibrating, Zero-Speed Differential Gear Tooth Sensor IC with Continuous Update ATS643LSH OPERATING CHARACTERISTICS using reference target 60-0, TA and VCC within specification, unless otherwise noted Characteristic Symbol Test Conditions Min. Typ. Max. Units 4.0 - 24 V VCC 0 5 V - 3.5 4.0 V ICC = 19 mA for ATS643-I1, and 19.8 mA for ATS643-I2; TA = 25C 28 - - V ATS643-I1 4.0 6 8.0 mA ATS643-I2 5.9 7 8.4 mA ATS643-I1 12.0 14.0 16.0 mA ATS643-I2 11.8 14.0 16.8 mA 1.85 - 3.05 - t < ton; dI/dt < 5 s - High - mA Target gear speed < 100 rpm - 1 2 ms RLOAD = 100 , CLOAD = 10 pF - 7 - mA/s RSENSE on high side (VCC pin); ICC = ICC(High) - Low - mV RSENSE on low side (GND pin); ICC = ICC(High) - High - mV ELECTRICAL CHARACTERISTICS Supply Voltage Undervoltage Lockout VCC VCC(UV) Supply Zener Clamp Voltage VZ ICC(Low) Supply Current ICC(High) Supply Current Ratio Operating; TJ < 165 C ICC(High)/ Ratio of high current to low current ICC(Low) POWER-ON CHARACTERISTICS Power-On State ICC(PO) Power-On Time1 ton OUTPUT STAGE Output Slew Rate2 dI/dt Output State VOUT Continued on the next page. Allegro MicroSystems, Inc. 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 3 Self-Calibrating, Zero-Speed Differential Gear Tooth Sensor IC with Continuous Update ATS643LSH OPERATING CHARACTERISTICS (continued) using reference target 60-0, TA and VCC within specification, unless otherwise noted Characteristic Symbol Test Conditions Min. Typ. Max. Units Reference Target 60-0 0 - 12,000 rpm Equivalent to f - 3dB 25 40 - kHz SWITCHPOINT CHARACTERISTICS Rotation Speed SROT Bandwidth BW Operate Point BOP % of peak to peak referenced from PDAC to NDAC, AG < AGMAX - 65 - % Release Point BRP % of peak to peak referenced from PDAC to NDAC, AG < AGMAX - 35 - % - - 3 Edge - - 3 Edge - 175 - mV - 60 - G - 9 - Bit CALIBRATION3 Initial Calibration Period CI AGC Calibration Disable Cf Start Mode Hysteresis Quantity of rising output (current) edges required for accurate edge detection Quantity of rising output (current) edges used for calibrating AGC POHYS DAC CHARACTERISTICS Dynamic Offset Cancellation Quantity of bits available for PDAC/NDAC tracking of both positive and negative signal peaks Tracking Data Resolution FUNCTIONAL CHARACTERISTICS Air Gap Range4 Maximum Operable Air Gap AG AG(opmax) Duty Cycle Variation DC Input Signal Range Sig Minimum Operable Input Signal Sig(opmin) DC within specification 0.5 - 2.5 mm Output switching (no missed edges); DC not guaranteed - - 2.75 mm Wobble < 0.5 mm, AG within specification - - 10 % DC within specification 40 - 1400 G Output switching (no missed edges); DC not guaranteed 30 - - G 1Power-On 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. 2dI Allegro MicroSystems, Inc. 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 4 Self-Calibrating, Zero-Speed Differential Gear Tooth Sensor IC with Continuous Update ATS643LSH REFERENCE TARGET, 60-0 (60 Tooth Target) Characteristics Symbol Test Conditions Typ. Units 120 mm Outside Diameter Do Outside diameter of target Face Width F Breadth of tooth, with respect to branded face 6 mm Circular Tooth Length t Length of tooth, with respect to branded face; measured at Do 3 mm Circular Valley Length tv Length of valley, with respect to branded face; measured at Do 3 mm Tooth Whole Depth ht 3 mm - - Material Symbol Key of Package Low Carbon Steel Reference Gear Magnetic Gradient Amplitude with Reference to Air Gap Peak-to-Peak Differential B* (G) 1800 1600 1400 1200 1000 800 Branded Face of Package 600 400 200 Reference Target 60-0 0 0.5 1 1.5 2 2.5 AG (mm) Reference Gear Magnetic Profile Two Tooth-to-Valley Transitions 700 Differential B* (G) 600 500 400 300 AG (mm) 0.50 0.75 1.00 1.25 1.50 1.75 2.00 200 100 0 -100 -200 -300 -400 2.00 mm AG -500 -600 0.50 mm AG -700 0 1 2 3 4 5 6 7 8 9 10 11 12 Gear Rotation () *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 Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 5 Self-Calibrating, Zero-Speed Differential Gear Tooth Sensor IC with Continuous Update ATS643LSH Characteristic Data Data taken from 3 lots, 30 pieces/lot; I1 trim Reference Target 60-0 Duty Cycle at 1000 RPM Duty Cycle at 1000 RPM 60 60 AG (mm) Duty Cycle (%) 50 Duty Cycle (%) 3.0 2.75 2.5 2.25 2.0 1.5 1.0 0.5 55 45 40 -50 55 50 TA (C) -40 0 25 85 150 45 40 0 50 100 150 200 0 0.5 1 1.5 TA (C) 2 2.5 3 3.5 AG (mm) Duty Cycle (25C) 60 Duty Cycle (%) AG (mm) 3.0 2.75 2.5 2.25 2.0 1.5 1.0 0.5 55 50 45 40 0 500 1000 1500 2000 2500 RPM Continued on the next page. Allegro MicroSystems, Inc. 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 6 Self-Calibrating, Zero-Speed Differential Gear Tooth Sensor IC with Continuous Update ATS643LSH Characteristic Data (continued) Data taken from 3 lots, 30 pieces/lot; I1 trim ICC (Low) ICC(Low) 9 26.5 20.0 12.0 4.0 8 TA (C) 7 7 6 6 5 5 4 4 3 -50 150 85 25 0 -40 8 Icc (mA) Icc (mA) 9 VCC 3 0 50 100 150 0 200 5 10 15 20 25 I CC(High) I CC(High) 17 17 V26.5V CC TA (C) 26.5 20V 20.0 12V 12.0 4V 4.0 16 150 85 25 0 -40 16 15 Icc (mA) Icc (mA) 15 14 14 13 13 12 12 11 50 100 150 200 0 5 10 TA (C) 15 20 25 30 Vcc (V) I+ Hysteresis of IICC Switching Due to B Switch to Low Output current in relation to sensed magnetic flux density. Transition through BOP must precede by transition through BRP. Switch to High ICC(High) ICC(Low) BRP BOP 0 ICC 11 -50 30 Vcc (V) TA (C) B+ BHYS Allegro MicroSystems, Inc. 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 7 Self-Calibrating, Zero-Speed Differential Gear Tooth Sensor IC with Continuous Update ATS643LSH THERMAL CHARACTERISTICS may require derating at maximum conditions, see application information Characteristic Symbol 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) RJA Maximum Allowable VCC (V) Package Thermal Resistance Max Units - - C/W - - C/W Power Derating Curve TJ(max) = 165C; ICC = ICC(max) 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 VCC(max) Low-K PCB (RJA = 84 C/W) Minimum-K PCB (RJA = 126 C/W) VCC(min) 20 Power Dissipation, PD (m W) Typ. 40 60 80 100 120 140 160 180 Maximum Power Dissipation, PD(max) TJ(max) = 165C; VCC = VCC(max); ICC = ICC(max) 1900 1800 1700 1600 1500 1400 1300 1200 1100 1000 900 800 700 600 500 400 300 200 100 0 Lo (R w- K J A = PC Mi n 84 B (R imu C mJ A = KP /W 12 ) 6 CB C/ W) 20 40 60 80 100 120 Temperature (C) 140 160 180 Allegro MicroSystems, Inc. 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 8 Self-Calibrating, Zero-Speed Differential Gear Tooth Sensor IC with Continuous Update ATS643LSH Functional Description Hall Technology. The ATS643 contains a single-chip differential Hall effect sensor IC, a samarium cobalt pellet, 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 IC, 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) 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 IC 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 package face) 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 IC 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 IC) passes the package face. In this configuration, the device output current switches to its high polarity when a tooth is the target feature nearest to the package. 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 package. 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 VPROC is directly proportional to the magnetic flux density, B, Mechanical Position (Target movement pin 1 to pin 4) Element Pitch Hall Element 2 Dual-Element Hall Effect Device incremental assembly costs for most applications. Hall Element 1 Hall IC Pole Piece (Concentrator) South Pole Back-biasing Rare-earth Pellet Case North Pole (Pin n >1 Side) (Pin 1 Side) Figure 1. Relative motion of the target is detected by the dual Hall elements mounted on the Hall IC. This tooth sensed earlier This tooth sensed later Target (Gear) Target Magnetic Profile +B Package Orientation to Target Package Branded Face Pin 4 Side Pin 1 Side Package IC Internal Differential Analog Signal, VPROC BOP(#1) BOP(#2) +t BRP(#1) Branded Face of Package Rotating Target IC Internal Switch State Off On Off On +t 1 4 IC Output Signal, IOUT +t 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 package (see figure 3). A right-to-left (pin 4 to pin 1) rotation inverts the output signal polarity. 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 Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 9 Self-Calibrating, Zero-Speed Differential Gear Tooth Sensor IC with Continuous Update ATS643LSH 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 IC switch turn-on and turn-off. 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 release point, BRP , the switch toggles from on to off. (A) TEAG varying; cases such as eccentric mount, out-of-round region, normal operation position shift 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. (B) Internal analog signal, VPROC, typically resulting in the IC V+ Smaller TEAG IC Target Smaller TEAG Larger TEAG VPROC (V) Target Hysteresis Band (Delimited by switchpoints) Larger TEAG IC Smaller TEAG 0 360 Target Rotation () (C) Referencing the internal analog signal, VPROC, to continuously update device response 1 2 3 4 Determinant Peak Values BOP(#1) BRP(#1) Pk(#1), Pk(#2) Pk(#2), Pk(#3) BOP(#2) BRP(#2) Pk(#3), Pk(#4) Pk(#4), Pk(#5) BOP(#3) BRP(#3) Pk(#5), Pk(#6) Pk(#6), Pk(#7) BOP(#4) Pk(#7), Pk(#8) BRP(#4) Pk(#8), Pk(#9) V+ Pk(#9) Pk(#1) Pk(#3) Pk(#7) Pk(#5) VPROC (V) BHYS Switchpoint BOP(#1) BOP(#2) BOP(#4) BOP(#3) BRP(#1) BRP(#3) BRP(#2) Pk(#4) BRP(#4) Pk(#6) Pk(#8) Pk(#2) BHYS(#1) BHYS(#2) BHYS(#3) BHYS(#4) t+ Figure 4. The Continuous Update algorithm allows the Allegro IC 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 IC 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 Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 10 Self-Calibrating, Zero-Speed Differential Gear Tooth Sensor IC with Continuous Update ATS643LSH 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), 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 package when power-on occurs. Target (Gear) 1 Package Position 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 AGC Calibration Running Mode VPROC Power-on over tooth 3 Output Start Mode Hysteresis Overcome 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 package 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 Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 11 Self-Calibrating, Zero-Speed Differential Gear Tooth Sensor IC with Continuous Update ATS643LSH 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 IC on such spurious signals. Calibration can be performed using the actual target features. 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. Target, Gear Package Position Relative to Target 1 5 2 Target Magnetic Profile Differential Signal, VPROC BRP(#1) Start Mode Hysteresis, POHYS BOP(#1) 1 BOP(#2) 2 3 4 5 Output Signal, IOUT 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 Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 12 Self-Calibrating, Zero-Speed Differential Gear Tooth Sensor IC with Continuous Update ATS643LSH 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 IC. 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 power- on, the device determines the peak-to-peak amplitude of the signal generated by the target. The gain of the IC 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. Ferrous Target Mechanical Profile V+ VCC (Optional) 1 2 ATS643 3 Internal Differential Analog Signal Response, without AGC AGSmall 0.01 F (Optional) AGLarge V+ 4 100 Figure 7. Typical basic circuit for proper device operation. Internal Differential Analog Signal Response, with AGC AGSmall AGLarge 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 Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 13 ATS643LSH Self-Calibrating, Zero-Speed Differential Gear Tooth Sensor IC with Continuous Update Power Derating 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 (1) T = PD x RJA (2) TJ = TA + T 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. (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 Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 14 Self-Calibrating, Zero-Speed Differential Gear Tooth Sensor IC with Continuous Update ATS643LSH Package SH, 4-pin SIP F 5.500.05 1.10 E 1.10 F B 8.000.05 LLLLLLL NNN 5.800.05 E1 E2 YYWW Branded Face 1.700.10 5.000.10 D 4.000.10 1 2 3 4 = Supplier emblem L = Lot identifier N = Last three numbers of device part number Y = Last two digits of year of manufacture W = Week of manufacture A 0.600.10 Standard Branding Reference View 0.710.05 For Reference Only, not for tooling use (reference DWG-9003) Dimensions in millimeters A Dambar removal protrusion (16X) 24.650.10 B Metallic protrusion, electrically connected to pin 4 and substrate (both sides) C Thermoplastic Molded Lead Bar for alignment during shipment +0.06 0.38 -0.04 1.000.10 13.100.10 D Branding scale and appearance at supplier discretion E Active Area Depth 0.43 mm REF F Hall elements (E1, E2); not to scale A 1.0 REF 1.600.10 C 1.270.10 0.710.10 0.710.10 5.500.10 Copyright (c)2004-2009, Allegro MicroSystems, Inc. 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's products are not to be used in life support devices or systems, if a failure of an Allegro product can reasonably be expected to cause the failure of that life support device or system, or to affect the safety or effectiveness of that device or system. 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. For the latest version of this document, visit our website: www.allegromicro.com Allegro MicroSystems, Inc. 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 15