ATS643LSH Self-Calibrating, Zero-Speed Differential Gear Tooth Sensor with Continuous Update Package SH, 4-pin SIP 12 34 1. VCC 2. No connection (float or tie to VCC) 3. Test pin (float or tie to GND) 4. GND 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 fine-tune the switchpoints while in running mode, maintaining 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. Features and Benefits ABSOLUTE MAXIMUM RATINGS Supply Voltage, VCC ..................See Power Derating Reverse-Supply Voltage, VRCC ........................ –18 V Operating Temperature Ambient, TA................................ –40ºC to 150ºC Maximum Junction, TJ(max)........................165ºC Storage Temperature, TS .................. –65ºC to 170ºC • Fully-optimized differential digital gear tooth sensor • Precise duty cycle accuracy throughout temperature range • Single chip-IC for high reliability • Large operating air gaps • Internal current regulator for 2-wire operation • <2 ms power-on time • Small mechanical size (8 mm diameter x 5.5 mm depth) • AGC and reference adjust circuit • True zero-speed operation • Switchpoints air gap independent • Undervoltage lockout • Digital output representing gear profile • Wide operating voltage range • Defined power-on state Use the following complete part numbers when ordering: ATS643-DS, Rev. 1 Part Number Package ICC Typical ATS643LSH-I1 4-pin plastic SIP 6.0 Low to 14.0 High mA ATS643LSH-I2 4-pin plastic SIP 7.0 Low to 14.0 High mA Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com ATS643LSH Self-Calibrating, Zero-Speed Differential GTS with Continuous Update Functional Block Diagram VCC (Pin 1) Hall AMP Offset Adjust AGC Internal Regulator PDAC ThresholdP Reference Generator and Updates Threshold Logic ThresholdN NDAC GND (Pin 4) 2 ATS643-DS, Rev. 1 Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com ATS643LSH Self-Calibrating, Zero-Speed Differential GTS with Continuous Update 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 = 25°C 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 µs – High – mA Target gear speed < 100 rpm – 1 2 ms RLOAD = 100 Ω, CLOAD = 10 pF – 7 – mA/µs 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. 3 ATS643-DS, Rev. 1 Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com ATS643LSH Self-Calibrating, Zero-Speed Differential GTS with Continuous Update 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 4 ATS643-DS, Rev. 1 Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com ATS643LSH Self-Calibrating, Zero-Speed Differential GTS with Continuous Update 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 sensor 6 mm Circular Tooth Length t Length of tooth, with respect to sensor; measured at Do 3 mm Circular Valley Length tv Length of valley, with respect to sensor; measured at Do 3 mm Tooth Whole Depth ht 3 mm – – Material Low Carbon Steel Symbol Key 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 Sensor 600 400 Reference Target 60-0 200 0 0.5 1 1.5 2 2.5 AG (mm) Reference Gear Magnetic Profile Two Tooth-to-Valley Transitions 700 Differential B* (G) 600 500 400 300 200 100 AG (mm) 0.50 0.75 1.00 1.25 1.50 1.75 2.00 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). 5 ATS643-DS, Rev. 1 Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com ATS643LSH Self-Calibrating, Zero-Speed Differential GTS with Continuous Update 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) 3.0 2.75 2.5 2.25 2.0 1.5 1.0 0.5 50 55 Duty Cycle (%) Duty Cycle (%) 55 50 45 40 –50 TA (ºC) -40 0 25 85 150 45 0 50 100 TA (°C) 150 200 40 0 0.5 1 1.5 2 2.5 3 3.5 AG (mm) Duty Cycle (25°C) 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. 6 ATS643-DS, Rev. 1 Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com ATS643LSH Self-Calibrating, Zero-Speed Differential GTS with Continuous Update 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 (ºC) 7 6 7 6 5 5 4 4 3 –50 3 0 50 TA (°C) 100 150 150 85 25 0 –40 8 Icc (mA) Icc (mA) 9 VCC 200 0 5 10 15 20 25 I CC(High) I CC(High) 17 17 V26.5V CC TA (ºC) 26.5 20V 20.0 12V 12.0 4V 4.0 16 Icc (mA) Icc (mA) 14 15 14 13 13 12 12 0 50 TA (°C) 100 150 150 85 25 0 –40 16 15 11 –50 30 Vcc (V) 11 200 0 5 10 15 20 25 30 Vcc (V) I+ Hysteresis of ∆IICC Switching Due to ∆B Switch to High Switch to Low Output current in relation to sensed magnetic flux density. Transition through BOP must precede by transition through BRP. ICC ICC(High) BRP BOP ICC(Low) B+ BHYS 7 ATS643-DS, Rev. 1 Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com ATS643LSH Self-Calibrating, Zero-Speed Differential GTS with Continuous Update 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) RθJA Maximum Allowable VCC (V) Package Thermal Resistance Max Units – – ºC/W – – ºC/W Power Derating Curve TJ(max) = 165ºC; 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 (RθJA = 84 ºC/W) Minimum-K PCB (RθJA = 126 ºC/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) = 165ºC; 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 θJ A = PC Mi n 84 B (R imu ºC mθJ A = KP /W 12 ) 6 º CB C/ W) 20 40 60 80 100 120 Temperature (°C) 140 160 180 8 ATS643-DS, Rev. 1 Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com ATS643LSH Self-Calibrating, Zero-Speed Differential GTS with Continuous Update Functional Description 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 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) Target (Gear) 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 This tooth sensed earlier This tooth sensed later Target (Gear) Target Magnetic Profile +B Back-biasing Magnet North Pole Sensor Orientation to Target Case (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. Pin 4 Side Sensor Branded Face Sensor Sensor Internal Differential Analog Signal, VPROC BOP(#1) BOP(#2) +t BRP(#1) Branded Face of Sensor Rotating Target Pin 1 Side Sensor Internal Switch State Off 1 4 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. On Sensor Output Signal, IOUT Off On +t +t Figure 3. The magnetic profile reflects the geometry of the target, allowing the ATS643 to present an accurate digital output response. 9 ATS643-DS, Rev. 1 Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com ATS643LSH Self-Calibrating, Zero-Speed Differential GTS with Continuous Update 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 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. (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 Smaller TEAG Target Sensor VPROC (V) Larger TEAG Target Smaller TEAG Hysteresis Band (Delimited by switchpoints) Larger TEAG Sensor 360 0 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) VPROC (V) BHYS Switchpoint Pk(#7) Pk(#5) 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 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. 10 ATS643-DS, Rev. 1 Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com ATS643LSH Self-Calibrating, Zero-Speed Differential GTS with Continuous Update 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 sensor when power-on occurs. 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 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 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. 11 ATS643-DS, Rev. 1 Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com ATS643LSH Self-Calibrating, Zero-Speed Differential GTS 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 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). 12 ATS643-DS, Rev. 1 Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com ATS643LSH Self-Calibrating, Zero-Speed Differential GTS with Continuous Update 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 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. Ferrous Target Mechanical Profile V+ VCC (Optional) 1 2 ATS643 3 Internal Differential Analog Signal Response, without AGC AGSmall 0.01 µF (Optional) AGLarge V+ 4 100 Ω 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. 13 ATS643-DS, Rev. 1 Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com ATS643LSH Self-Calibrating, Zero-Speed Differential GTS 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, RθJA, 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, RθJC, is relatively small component of RθJA. 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 × IIN (1) ∆T = PD × RθJA (2) TJ = TA + ∆T (3) Example: Reliability for VCC at TA = 150°C, package L-I1, using minimum-K PCB Observe the worst-case ratings for the device, specifically: RθJA = 126°C/W, TJ(max) = 165°C, 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 ÷ RθJA = 15°C ÷ 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 RθJA. 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= 25°C, VCC = 12 V, ICC = 4 mA, and RθJA = 140 °C/W, then: PD = VCC × ICC = 12 V × 4 mA = 48 mW ∆T = PD × RθJA = 48 mW × 140 °C/W = 7°C TJ = TA + ∆T = 25°C + 7°C = 32°C A worst-case estimate, PD(max), represents the maximum allowable power level (VCC(max), ICC(max)), without exceeding TJ(max), at a selected RθJA and TA. 14 ATS643-DS, Rev. 1 Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com ATS643LSH Self-Calibrating, Zero-Speed Differential GTS with Continuous Update Package SH, 4-pin SIP 5.5 .217 C 8.0 .315 B 5.8 .228 2.9 4.0 5.0 .244 .114 .157 0.38 .015 A 1.7 .067 1 2 3 4 1.08 .043 20.95 .825 1 .039 13.05 .514 A 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 B Metallic protrusion, electrically connected to pin 4 and substrate (both sides) C Active Area Depth 0.43 mm [.017] D Thermoplastic Molded Lead Bar for alignment during shipment 15 ATS643-DS, Rev. 1 Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com ATS643LSH Self-Calibrating, Zero-Speed Differential GTS 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 © 2004 Allegro MicroSystems, Inc. 16 ATS643-DS, Rev. 1 Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com