ATS674

ATS673 and ATS674 Self-Calibrating TPOS Gear Tooth Sensor Optimized for Automotive Cam Sensing Applications Features and Benefits ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ Tight timing accuracy over operating temperature range True zero-speed operation TPOS (True Power-On State) Air-gap-independent switchpoints High immunity to vibration Large operating air gaps Operation with supply voltages down to 3.3 V Digital output representing target profile Single-chip solution for high reliability Optimized Hall IC/magnet system Description Recognizing the increasingly stringent requirements for EMC/ EMI in automotive applications, Allegro has taken the necessary steps to design devices that are capable of withstanding the effects of radiated and conducted transients. The ATS673 and ATS674 devices have been designed specifically for this purpose. Advanced circuitry on the die allows them to survive positive and negative transient pulses on both the input and output. The ATS673 and ATS674 devices retain all of the same characteristics as the ATS671 and ATS672. The devices remain true zero-speed gear tooth sensors with optimized Hall IC/ magnet configuration in an SIP (single in-line package). The SIP assembly consists of a molded package that holds together a samarium cobalt magnet, a pole piece, and a true zero-speed Hall IC that has been optimized to the magnetic circuit. The sensor incorporates a single element Hall IC that switches in response to magnetic signals created by a ferrous target. The IC contains a sophisticated digital circuit designed to eliminate the detrimental effects of magnet and system offsets. Signal processing is used to provide zero-speed Continued on the next page… Packages: 4 pin SIP (suffix SE) Continued on the next page… Not to scale Functional Block Diagram V+ VCC Voltage Regulator (Analog) VREG(A) Voltage Regulator (Digital) VREG(D) Hall Amp Offset Adjust Temperature Coefficient Adjust Automatic Gain Control LPF VPROC Offset TC VREF 9-Bit PDAC 9 Comp_P 0.1 μF CBYPASS Continuous Update Logic Output State Clock Continuous Update Logic Comp_N Output State 9-Bit Counter Clock 9-Bit Counter Threshold Output 9 9-Bit NDAC TPOS VREG(A) Power-On Reset VREG(D) Output Driver Threshold Comparator VOUT TPOS Trim GND (Recommended) TEST ATS673-DS, Rev. 1 ATS673 and ATS674 Self-Calibrating TPOS Gear Tooth Sensor Optimized for Automotive Cam Sensing Applications even in the presence of gear eccentricity. Hysteresis in the thresholds reduces the negative effects of anomalies in the magnetic signal (such as magnetic overshoot) associated with the targets used in many automotive applications. The ATS673 and 674 also include a low bandwidth filter that increases the noise immunity and the signal to noise ratio of the sensor. Two options are available for output polarity, low over tooth (LT) and high over tooth (HT). For applications requiring absolute accuracy use the ATS674. The ATS673 should be used for targets with high wobble. Features and Benefits (continued) ▪ AGC and reference adjust circuit ▪ Undervoltage lockout Description (continued) performance independent of air gap and also to dynamically adapt device performance to the typical operating conditions found in automotive applications, particularly cam sensing applications (reduced vibration sensitivity). High-resolution (9-bit) peak detecting DACs are used to set the adaptive switching thresholds of the devices, ensuring high accuracy Selection Guide Part Number ATS673LSETN-LT-T ATS673LSETN-HT-T ATS674LSETN-LT-T ATS674LSETN-HT-T 1Pb-based Pb-free1 Yes Yes Yes Yes VOUT (Over Tooth) Low High Low High Application High target wobble Packing2 13-in. reel, 450 pieces/reel High absolute edge detection accuracy 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: ATS673LSETN-LT, ATS673LSETN-HT, ATS674LSETN-LT, and ATS674LSETN-HT. 2Contact Allegro for additional packing options. Absolute Maximum Ratings Characteristic Supply Voltage Reverse-Supply Voltage Continuous Output Current Reverse Output Current Operating Ambient Temperature Maximum Junction Temperature Storage Temperature Symbol VCC VRCC IOUT IROUT TA TJ(max) Tstg Range L Notes Rating 28 –18 20 50 –40 to 150 165 –65 to 170 Units V V mA mA ºC ºC ºC Pin-out Diagram Terminal List Name VCC VOUT TEST GND Device output For Allegro use, float or tie to GND Ground terminal Description Connects power supply to chip Number 1 2 3 4 12 34 Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 2 ATS673 and ATS674 Self-Calibrating TPOS Gear Tooth Sensor Optimized for Automotive Cam Sensing Applications OPERATING CHARACTERISTICS Valid at TA = –40°C to 150°C, TJ ≤ TJ(max), over full range of AG, unless otherwise noted Characteristic Supply Voltage Undervoltage Lockout Supply Zener Clamp Voltage Supply Zener Current2 Supply Current Reverse Supply Current POWER-ON CHARACTERISTICS Power-On Time3 OUTPUT CHARACTERISTICS Low Output Voltage Output Zener Voltage Output Current Limit Output Leakage Current Output Rise Time Output Fall Time VOUT(Sat) VZOUT IOUTLIM IOUTOFF tr tf VOUT ISINK = 15 mA, Output = ON IOUT = 3 mA, TA = 25°C Output = ON, VOUT = 12 V Output = OFF, VOUT = VCC(Max) 10/90% points; RLOAD = 500 Ω, CLOAD = 10 pF, TA = 25°C 10/90% points; RLOAD = 500 Ω, CLOAD = 10 pF, TA = 25°C Over tooth HT device option Over valley LT device option Over tooth Over valley – 30 35 – – – – – – – 200 – 57 – 0.9 0.5 HIGH LOW LOW HIGH 450 – 90 10 5 5 – – – – mV V mA μA μs μs V V V V tPO Gear Speed < 100 rpm; VCC > VCC(Min) – – 500 μs Symbol VCC VCCUV VZSupply IZSupply ICC IRCC Test Conditions Operating; TJ < TJ(Max) ICC = ICC(Max) + 3 mA, TA = 25°C VSupply = 27 V Output = OFF or ON VRCC = –18 V Min. 3.3 – 28 – 3 – Typ.1 – – 31 – 6.5 –5 Max. 26.5 13 mm • Valley depth, ht > 5 mm • Tooth thickness, F ≥ 5 mm t Air Gap Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 6 ATS673 and ATS674 Self-Calibrating TPOS Gear Tooth Sensor Optimized for Automotive Cam Sensing Applications Characteristic Data: Electrical Supply Current (On) Versus Ambient Temperature 11 10 11 10 VCC (V) 26.5 15.0 3.3 Supply Current (Off) Versus Ambient Temperature ICC(OFF) (mA) 9 9 8 7 6 5 4 3 VCC (V) 26.5 15.0 3.3 ICC(ON) (mA) 8 7 6 5 4 3 -50 -25 0 25 50 75 100 125 150 175 -50 -25 0 25 50 75 100 125 150 175 TA (°C) TA (°C) Supply Current (On) Versus Supply Voltage 11 10 11 10 9 TA (°C) -40 0 25 85 150 Supply Current (Off) Versus Supply Voltage ICC(OFF) (mA) ICC(ON) (mA) 9 8 7 6 5 4 3 0 5 10 15 20 25 30 TA (°C) -40 0 25 85 150 8 7 6 5 4 3 0 5 10 15 20 25 30 VCC (V) VCC (V) Output Voltage (Low) Versus Ambient Temperature 500 Output Leakage Current (Off) Versus Ambient Temperature 10 8 IOUT (mA) 20 15 10 400 VOUT(SAT) (mV) 300 IOUT(OFF) (uA) 6 4 2 0 200 100 0 -50 -25 0 25 50 75 100 125 150 175 -50 -25 0 25 50 75 100 125 150 175 TA (°C) TA (°C) Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 7 ATS673 and ATS674 Self-Calibrating TPOS Gear Tooth Sensor Optimized for Automotive Cam Sensing Applications Characteristic Data: Relative Timing Accuracy ATS673 Relative Timing Accuracy Versus Air Gap Rising Mechanical Edge 1000 rpm, Relative to 0.5 mm Air Gap 0.0 -0.1 ATS673 Relative Timing Accuracy Versus Air Gap Falling Mechanical Edge 1000 rpm, Relative to 0.5 mm Air Gap 1.2 1.0 TA (°C) –40 0 25 85 150 Edge Position (°) -0.2 -0.3 -0.4 -0.5 -0.6 -0.7 -0.8 0.5 Edge Position (°) 0.8 0.6 0.4 0.2 0.0 TA (°C) –40 0 25 85 150 1.0 1.5 2.0 2.5 3.0 0.5 1.0 1.5 2.0 2.5 3.0 AG (mm) AG (mm) ATS674 Relative Timing Accuracy Versus Air Gap Rising Mechanical Edge 1000 rpm, Relative to 0.5 mm Air Gap 0.0 -0.1 ATS674 Relative Timing Accuracy Versus Air Gap Falling Mechanical Edge 1000 rpm, Relative to 0.5 mm Air Gap 1.2 1.0 Edge Position (°) -0.2 -0.3 -0.4 -0.5 -0.6 -0.7 -0.8 Edge Position (°) TA (°C) –40 0 25 85 150 TA (°C) 0.8 0.6 0.4 0.2 0.0 –40 0 25 85 150 0.5 1.0 1.5 2.0 2.5 3.0 0.5 1.0 1.5 2.0 2.5 3.0 AG (mm) AG (mm) Relative Timing Accuracy Versus Air Gap Rising Mechanical Edge 1.5 mm Air Gap, Relative to 0.5 mm Air Gap 0.40 0.30 0.40 0.30 Relative Timing Accuracy Versus Air Gap Falling Mechanical Edge 1.5 mm Air Gap, Relative to 0.5 mm Air Gap Edge Position (°) 0.20 0.10 0 -0.10 -0.20 -0.30 -0.40 0 500 1000 1500 2000 2500 ATS673 ATS674 Edge Position (°) 0.20 0.10 0 -0.10 -0.20 -0.30 -0.40 0 500 1000 1500 2000 2500 ATS673 ATS674 Gear Speed (rpm) Gear Speed (rpm) Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 8 ATS673 and ATS674 Self-Calibrating TPOS Gear Tooth Sensor Optimized for Automotive Cam Sensing Applications Operational Description Assembly Description The ATS673 and ATS674 true zero-speed gear tooth sensors have a 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 Hall effect sensor IC, a 4-pin leadframe and a specially designed rare-earth magnet. The Hall IC supports a Hall element that measures the magnetic gradient created by the passing of a ferrous object. This is illustrated in figure 2. The difference in the magnetic gradients created by teeth and valleys allows the devices to generate a digital output signal. Output After proper power is applied to the devices, they are then capable of providing digital information that is representative of the profile of a rotating gear, as illustrated in figure 3. 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) High-B field Hall IC North Pole Back-Biasing magnet Plastic South Pole (A) (B) Sensor Device Pole piece (Concentrator) Low-B field Hall element Leadframe Figure 2. Device Cross Section. Motion of the target is detected by the Hall element mounted on the Hall IC. Panel A, the presence of a tooth feature on the target is distinguished by a high magnetic flux density, B. Panel B, the presence of a valley feature is distinguished by its low magnetic flux density. Target Mechanical Profile B BIN 0 Target Magnetic Profile -LT Option Sensor Output Switch State Sensor Output Electrical Profile On V+ VOUT Off On Off On Off On Off -HT Option Sensor Output Switch State Sensor Output Electrical Profile Off On V+ VOUT Off On Off On Off On Figure 3. 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 9 ATS673 and ATS674 Self-Calibrating TPOS Gear Tooth Sensor Optimized for Automotive Cam Sensing Applications TPOS (True Power-On State) Operation Under specified operating conditions, the devices are guaranteed to attain a specified output voltage polarity at power-on, in relation to the target feature nearest the device at that time. Both devices offer the options of either high or low polarity over initial tooth or valley. This polarity also applies throughout device operation. Start-Up Detection These devices provide an output polarity transition at the first mechanical edge after power-on. 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 ATS673 and ATS674 contain 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 These devices contain a self-calibrating Hall effect IC that provides a Hall element, 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 μF 3 ATS673/674 TEST 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 10 ATS673 and ATS674 Self-Calibrating TPOS Gear Tooth Sensor Optimized for Automotive Cam Sensing Applications AGC (Automatic Gain Control) The AGC feature is implemented by a unique patented selfcalibrating circuitry. After each power-on, the devices measure 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. This feature ensures that operational characteristics are isolated from the effects of changes in AG. The effect of AGC is shown in figure 7. Magnetic Flux Density Versus Target Edge Position 600 500 Flux Density, B (G) AG (mm): 1.50 400 300 200 100 0 0 10 20 30 40 2.00 2.50 3.00 3.50 50 60 70 80 90 Target Rotation (°) Internal Analog Signal after AGC Versus Target Edge Position 2.0 AG (mm): 1.5 VPROC (V) 1.50 2.00 2.50 3.00 3.50 1.0 0.5 0 0 10 20 30 40 50 60 70 80 90 Target Rotation (°) Figure 7. Effect of AGC. The upper panel shows the magnetic gradient detected at the Hall element, with no amplification. The lower panel displays the corresponding internal processed signal, VPROC. This normalized electrical signal allows optimal performance by the rest of the circuits that reference this signal. Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 11 ATS673 and ATS674 Self-Calibrating TPOS Gear Tooth Sensor Optimized for Automotive Cam Sensing Applications Switchpoints Switchpoints in the ATS673 and ATS674 are established dynamically as a percentage of the amplitude of the signal, VPROC, after normalization with AGC. Two DACs track the peaks of VPROC (see the Update subsection). The switching thresholds are established at fixed percentages of the values held in the two DACs. The value of the thresholds has been carefully selected, where the signal is steepest and least affected by air gap variation, thus providing the most accurate and consistent switching. The low hysteresis, 10%, provides high performance over various air gaps while maintaining 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. Target Mechanical Profile V+ 100 VPROC (%) BOP% BRP% 0 Device State -LT option -HT option On Off Off On On Off Off On 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. Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 12 ATS673 and ATS674 Update Self-Calibrating TPOS Gear Tooth Sensor Optimized for Automotive Cam Sensing Applications 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 devices use historical data to provide the switching thresholds for a given edge. The ATS673 and ATS674 incorporate an algorithm that continuously monitors the system and updates the switching thresholds accordingly. The switchpoint for each transition is determined by the previous two transitions. Because variations are tracked (A) TEAG varying; cases such as eccentric mount, out-of-round region, normal operation position shift V+ (B) Internal analog signal, VPROC, typically resulting in the sensor Smaller TEAG Larger TEAG VPROC (V) Smaller TEAG Target Target Sensor Smaller TEAG Sensor Larger TEAG 0 Hysteresis Band (Delimited by switchpoints) 360 Target Rotation (°) (C) Referencing the internal analog signal, VPROC, to continuously update device response Switchpoint BOP1 BRP1 BOP2 BRP2 BOP3 BRP3 BOP4 BRP4 Determinant Peak Values Pk1, Pk2 Pk2, Pk3 Pk3, Pk4 Pk4, Pk5 Pk5, Pk6 Pk6, Pk7 Pk7, Pk8 Pk8, Pk9 V+ Pk1 Pk3 BHYS BHYS Pk7 Pk5 BHYS Pk9 BHYS VPROC (V BOP1 BRP1 BOP2 BOP3 BRP2 BRP3 BOP4 BRP4 Pk4 Pk2 BHYS BHYS Pk6 Pk8 BHYS BHYS t+ Figure 9. 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 13 ATS673 and ATS674 Self-Calibrating TPOS Gear Tooth Sensor Optimized for Automotive Cam Sensing Applications Sensor and Target Evaluation Magnetic Profile In order to establish the proper operating specification for a particular sensor device 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 8X reference target. A pair of curves can be derived from this map data, and be used to describe the tooth and valley magnetic field strength, B, 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, so the system designer can determine the maximum allowable AG for the sensor and target system. One can also determine the TPOS air gap capabilities of the sensor by comparing the minimum tooth signal to the maximum valley signal. Magnetic Map, Reference Target 8X with SE Package 1600 1400 1200 Flux Density, B (G) 1000 800 600 400 200 0 0 60 120 180 240 300 360 Target Rotation (°) Air Gap Versus Magnetic Field, Reference Target 8X with SE Package 1300 1200 1100 1000 Flux Density, B (G) 900 800 700 600 500 400 300 200 100 0 0 1.0 2.0 3.0 4.0 5.0 6.0 Tooth Valley AG (mm) Figure 10. Magnetic Data for the 8X Reference Target and SE package. Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 14 ATS673 and ATS674 Self-Calibrating TPOS Gear Tooth Sensor Optimized for Automotive Cam Sensing Applications repower 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. Accuracy While the update algorithm will allow the sensor devices 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 Sensor Evaluation: EMC Characterization Only Test Name* Reference Specification AEC-Q100-002 AEC-Q100-003 ISO 7637-1 ISO 11452-7 ISO 11452-4 ISO 11452-3 ESD – Human Body Model ESD – Machine Model Conducted Transients Direct RF Injection Bulk Current Injection TEM Cell *Please contact Allegro for EMC performance Related Documents Documents that can be found on the Allegros web site,: www.allegromicro.com: • Definition of Terms (Pub 26004) • Hall-Effect Devices: Soldering, Gluing, Potting, Encapsulating, and Lead forming (AN27703.1) • Storage of Semiconductor Devices (Pub 26011) • Hall Effect Applications Guide (Pub 27701) • Applications Note: Back-Biased Packaging Advances (SE, SG & SH versus SA & SB) Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 15 ATS673 and ATS674 Self-Calibrating TPOS Gear Tooth Sensor Optimized for Automotive Cam Sensing Applications Power Derating THERMAL CHARACTERISTICS may require derating at maximum conditions, see application information Characteristic Package Thermal Resistance Symbol RθJA Test Conditions* 1-layer PCB with copper limited to solder pads 1-layer PCB with copper limited to solder pads and 3.57 in.2 (23.03 cm2) of copper area each side Value Units 101 77 ºC/W ºC/W *Additional information is available on the Allegro Web site. Power Derating Curve 30 VCC(max) 25 Maximum Allowable VCC (V) 20 15 1-Layer PCB (RθJA = 77 ºC/W) Pads Only PCB (RθJA = 101 ºC/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) Mi (R nim um θJ A= 10 K P 1 º CB C/ W ) L (R owK θJ A = PC 77 B ºC /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 16 ATS673 and ATS674 Self-Calibrating TPOS Gear Tooth Sensor Optimized for Automotive Cam Sensing Applications 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 ΔT = PD × RθJA TJ = TA + ΔT (1) (2) (3) Example: Reliability for VCC at TA = 150°C, package SE, using minimum-K PCB. Observe the worst-case ratings for the device, specifically: RθJA = 101°C/W, TJ(max) = 165°C, VCC(max) = 26.5 V, and ICC(max) = 11 mA. Note that ICC(max) at TA = 150°C is lower than the ICC(max) at TA = 25°C given in the Operating Characteristics table. Calculate the maximum allowable power level, PD(max). First, invert equation 3: ΔTmax = 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) = ΔTmax ÷ RθJA = 15°C ÷ 101 °C/W = 91 mW Finally, invert equation 1 with respect to voltage: VCC(est) = PD(max) ÷ ICC(max) = 91 mW ÷ 11 mA = 8.3 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, VIN = 12 V, IIN = 4 mA, and RθJA = 140 °C/W, then: PD = VIN × IIN = 12 V × 4 mA = 48 mW ΔT = PD × RθJA = 48 mW × 140 °C/W = 7°C TJ = TA + ΔT = 25°C + 7°C = 32°C A worst-case estimate, PD(max), represents the maximum allowable power level, without exceeding TJ(max), at a selected RθJA and TA. Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 17 ATS673 and ATS674 Self-Calibrating TPOS Gear Tooth Sensor Optimized for Automotive Cam Sensing Applications Package SE, 4-Pin SIP 7 .276 10 .394 C B 3.3 .130 E 6.2 .244 4.9 .193 1.3 .051 A 0.38 .015 1.08 .043 20.95 .825 11.6 .457 1 2 3 4 A D 0.6 .240 1.27 .050 2 .079 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 mm [.017] D Thermoplastic Molded Lead Bar for alignment during shipment E Hall element (not to scale) Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 18 ATS673 and ATS674 Self-Calibrating TPOS Gear Tooth Sensor Optimized for Automotive Cam Sensing Applications 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; 6,297,627; 6,525,531; 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 © 2005, 2006 Allegro MicroSystems, Inc. Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 19