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ATS642LSH
Two-Wire True Zero Speed Miniature Differential Peak-Detecting Gear Tooth Sensor with Continuous Calibration
The ATS642LSH is an optimized Hall effect sensing integrated circuit and magnet combination that provides a user-friendly solution for true zero-speed digital gear-tooth sensing in two-wire applications. The sensor 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. This small package, with optimized two-wire leadframe, 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 and signal processing that switches in response to differential magnetic signals created by ferrous gear teeth. The circuitry contains a sophisticated digital circuit to reduce magnet and system offsets, to calibrate the gain for air gap independent switchpoints, and to achieve true zero-speed operation. Signal optimization occurs at power-up through the combination of offset and gain adjust and is maintained throughout the operating time with the use of a running mode calibration. The running mode calibration allows immunity to environmental effects such as microoscillations of the target or sudden air gap changes. The regulated current output is configured for two wire applications and the sensor is ideally suited for obtaining speed and duty cycle information in ABS (antilock braking systems). The 1.5 mm Hall element spacing is optimized for fine pitch gear-tooth-based configurations. The package is lead (Pb) free, with 100% matte tin leadframe plating.
Package SH, 4-pin Module
12
34
1. VCC 2. No connection 3. Test pin (float or tie to GND) 4. GND
ABSOLUTE MAXIMUM RATINGS
Supply Voltage, VCC .......................................... 28 V Reverse-Supply Voltage, VRCC ........................ -18 V Operating Temperature Ambient, TA,............................... -40C to 150C Maximum Junction, TJ(max)........................165C Storage Temperature, TS .................. -65C to 170C
Features and Benefits
* Running mode calibration for continuous optimization * Single chip IC for high reliability * Internal current regulator for 2-wire operation * Small mechanical size (8 mm diameter x 5.5 mm depth) * Precise duty cycle signal over operating temperature range * Large operating air gaps * Automatic Gain Control (AGC) for air
gap independent switchpoints
* Automatic Offset Adjustment (AOA)
for signal processing optimization
* True zero-speed operation * Undervoltage lockout * Wide operating voltage range
Use the following complete part numbers when ordering:
Part Number
ATS642LSHTN-I1-T ATS642LSHTN-I2-T
ICC Typical
6.0 Low to 14.0 High mA 7.0 Low to 14.0 High mA
Packing*
Tape and reel, 13-inch reel 800 pieces/reel
*Contact Allegro for additional packing options.
ATS642LSH-DS
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
ATS642LSH
True Zero Speed Miniature Differential Peak-Detecting Gear Tooth Sensor
Functional Block Diagram
Hall Amplifier
Gain
VCC
Automatic Offset Control
AOA DAC
AGC DAC
Internal Regulator
Gain Control Tracking DAC Peak Hold
GND
Test Signals
Test
ATS642LSH-DS
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
2
ATS642LSH
True Zero Speed Miniature Differential Peak-Detecting Gear Tooth Sensor
OPERATING CHARACTERISTICS using reference target 60-0, TA and VCC within specification, unless otherwise noted CHARACTERISTIC Symbol Test Conditions Min. Typ.1 Max. Units
ELECTRICAL CHARACTERISTICS Supply Voltage2 Undervoltage Lockout Supply Zener Clamp Voltage Supply Zener Current VCC VCC(UV) VZ IZ ICC(Low) Supply Current ICC(High) Supply Current Ratio Reverse Battery Current Operating; TJ < 165 C VCC 0 5 V and 5 0 V ICC = ICC(max) + 3 mA; TA = 25C Test conditions only; VZ = 28 V ATS642LSH-I1 ATS642LSH-I2 ATS642LSH-I1 ATS642LSH-I2 4.0 - 28 - 4.0 5.9 12.0 11.8 1.85 - - - - - 6.0 7.0 14.0 14.0 - - 24 4.0 - ICC(max)+ 3 mA 8.0 8.4 16.0 16.8 3.05 -5 V V V mA mA mA mA mA - mA
ICC(High)/ Ratio of high current to low current ICC(Low) IRCC VRCC = -18 V
POWER-ON STATE CHARACTERISTICS Power-On State3 Power-On Time4 OUTPUT STAGE Output Slew Rate5 dI/dt RLOAD = 100 , CLOAD = 10 pF - 10 - mA/s POS tPO t > tPO Target gear speed < 100 rpm - - ICC(High) 1 - 2 - ms
Continued on the next page.
ATS642LSH-DS
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
3
ATS642LSH
True Zero Speed Miniature Differential Peak-Detecting Gear Tooth Sensor
OPERATING CHARACTERISTICS (continued) using reference target 60-0, TA and VCC within specification, unless otherwise noted Characteristic Symbol Test Conditions Min. Typ.1 Max. Units
SWITCHPOINT CHARACTERISTICS Rotation Speed Analog Signal Bandwidth Operate Point Release Point CALIBRATION Initial Calibration DAC CHARACTERISTICS Allowable User-Induced Differential Offset FUNCTIONAL CHARACTERISTICS6 Operational Air Gap Range7 Maximum Operational Air Gap Range Duty Cycle Variation Duty Cycle Pitch Variance8 Operating Signal Range9 AG AGOP(max) DC EDC Sig SigOP(min) DC within specification Output switching (no missed edges); DC not guaranteed Wobble < 0.5 mm; Typical value at AG = 1.5 mm, for max., min., AG within specification AG = 1.5 mm Operating within specification Output switching (no missed edges); DC not guaranteed 0.5 - 41 - 30 20 - - - 1.5 - - 2.75 3 61 - 1000 - mm mm % % G G Output switching only; may not meet datasheet specifications - 60 - G CI Quantity of rising output (current) edges required for accurate edge detection - - 3 Edge SROT BW BOP BRP Reference Target 60-0 Equivalent to f - 3 dB Transitioning from ICC(High) to ICC(Low); positive peak referenced; AG < AGMAX Transitioning from ICC(Low) to ICC(High); negative peak referenced; AG < AGMAX 0 20 - - - 40 120 120 8,000 - - - rpm kHz mV mV
Minimum Operating Signal
1Typical 2Maximum
values are at TA = 25C and VCC = 12 V. Performance may vary for individual units, within the specified maximum and minimum limits. voltage must be adjusted for power dissipation and junction temperature; see Power Derating section. 3Please refer to Sensor Operation section, page 13. 4Power-On Time includes the time required to complete the internal automatic offset adjust. The DACs are then ready for peak acquisition. 5dI is the difference between 10% of I CC(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. 6Functional characteristics valid only if magnetic offset is within the specified range for Allowable User Induced Differential Offset. 7AG 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. 8E DC represents the difference between consecutive duty cycles, DC(n) - DC(n-1); Mean 3-sigma. 9In order to remain in specification, the magnetic gradient must induce an operating signal greater than the minimum value specified. This includes the effect of target wobble.
ATS642LSH-DS
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
4
ATS642LSH
True Zero Speed Miniature Differential Peak-Detecting Gear Tooth Sensor
REFERENCE TARGET, 60-0 (60 Tooth Target) Characteristics Outside Diameter Face Width Angular Tooth Thickness Angular Valley Thickness Tooth Whole Depth Material Symbol Do F t tv ht Low Carbon Steel Test Conditions Outside diameter of target Breadth of tooth, with respect to sensor Length of tooth, with respect to sensor Length of valley, with respect to sensor Typ. 120 6 3 3 3 - Units mm mm deg deg mm -
Air Gap Branded Face of Sensor tv
Symbol Key
t Do F ht
Reference Gear Magnetic Gradient Amplitude With Reference to Air Gap
800
700
Peak-to-Peak Differential B (G)
600 500 400 300 200 100 0 0.5 1 1.5 2 2.5 3
Branded Face of Sensor
Air Gap (mm)
Reference Target 60-0
Reference Gear Magnetic Profile Two Tooth-to-Valley Transitions
500 400 300 200 100 0 -100 -200
Air Gap
(mm) 0.50 0.75 1.00 1.25 1.50 1.75 2.00 2.25 2.50 2.75 3.00
Differential B* (G)
3.00 mm AG
-300
0.50 mm AG
-400 -500 0 2 4 6 8 10 12
Gear Rotation ()
ATS642LSH-DS
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
5
ATS642LSH
True Zero Speed Miniature Differential Peak-Detecting Gear Tooth Sensor Characteristic Data
I1 Trim
16
Supply Current (High) versus Ambient Temperature (ATS642-I1)
Supply Current (High) versus Supply Voltage (ATS642-I1)
16
15
ICC(HIGH) (mA)
15 VCC (V) 24 12 4
ICC(HIGH) (mA)
14
14
13
13
TA (C) -40 25 85 150
12 -50 0 50 TA (C) 100 150
12 0 5 10 VCC (V) 15 20 25
Supply Current (Low) versus Ambient Temperature (ATS642- I1)
8 8
Supply Current (Low) versus Supply Voltage (ATS642-I1)
7 Vcc (V) 24 12 4
ICC(LOW) (mA)
ICC(LOW) (mA)
7
TA (C) -40 25 150
6
6
5
5
4 -50 0 50
TA (C)
4 100 150 0 5 10 VCC (V) 15 20 25
ATS642LSH-DS
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
6
ATS642LSH
True Zero Speed Miniature Differential Peak-Detecting Gear Tooth Sensor
Duty Cycle versus Air Gap*
61 59 57 55
DC (%)
53 51 49 47 45 43 41 0.5 1.0 1.5 AG (mm) 2.0 2.5 3.0
TA (C) -40 25 150
*The trend of duty cycle versus air gap is driven by the actual magnetic profile of the target (see figure on page 5).
Duty Cycle versus Ambient Temperature
61 59 57 55
DC (%)
6 4 AG (mm) 0.5 1.5 2.75 2 0 -2 -4 -6 0 50 TA (C) 100 150 0.5
Duty Cycle Variance versus Air Gap Mean 3 Sigma, 25C
51 49 47 45 43 41 -50
EDC (%)
53
1.0
1.5 AG (mm)
2.0
2.5
3.0
ATS642LSH-DS
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
7
ATS642LSH
True Zero Speed Miniature Differential Peak-Detecting Gear Tooth Sensor Characteristic Allowable Air Gap Movement
60-0 (60 Tooth Target)
Allowable Air Gap Movement from TEAGCAL
1.2 1.0
TEAGOUT (mm)
0.8 0.6 0.4 0.2 0 -0.2 0 0.2 0.4 0.6 0.8 1.0 TEAGIN (mm) 1.2 1.4 1.6 1.8
The colored area in the chart above shows the region of allowable air gap movement within which the sensor will continue output switching. The output duty cycle is wholly dependent on the target's magnetic signature across the air gap range of movement, and may not always be within specification throughout the entire operating region (to AG(OPmax)).
(a) (b)
The axis parameters for the chart are defined in the drawings below. As an example, assume the case where the air gap is allowed to vary from from the nominal installed air gap (TEAGCAL , panel a) within the range defined by an increase of TEAGOUT = 0.35 mm (shown in panel b), and a decrease of TEAGIN = 0.65 mm (shown in panel c). This case is plotted with an "x" in the chart above.
(c)
Sensor
TEAGCAL
Sensor
Sensor
TEAG IN
TEAG OUT
For more information on these figures and the calculations used to generate them, please refer to the Applications Note Determining Allowable Air Gap Variation for the ATS642.
ATS642LSH-DS
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
8
ATS642LSH
True Zero Speed Miniature Differential Peak-Detecting Gear Tooth Sensor
THERMAL CHARACTERISTICS may require derating at maximum conditions, see application information
CHARACTERISTIC Package Thermal Resistance Symbol RJA TEST CONDITIONS* Single-layer PCB with copper limited to solder pads Two-layer PCB with 3.8 in.2 of copper area on each side connected with thermal vias and to device ground pin Value 126 84 Units C/W C/W
*Additional information is available on the Allegro Web site.
Power Derating Curve
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 60
VCC(max)
Maximum Allowable VCC (V)
(RJA = 84 C/W) (RJA = 126 C/W)
VCC(min)
80 100 120 140 160 180
Temperature (C)
Maximum Power Dissipation, PD(max)
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)
(R
J
A
(R
=
J
84
A
=1
C
26
/W
C
)
/W
)
60
80 100 120 Temperature (C)
140
160
180
ATS642LSH-DS
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
9
ATS642LSH
True Zero Speed Miniature Differential Peak-Detecting Gear Tooth Sensor Functional Description
Sensing Technology Output Polarity
The gear tooth sensor subassembly contains a single-chip differential Hall effect sensor IC, an optimized samarium cobalt magnet, and a flat ferrous pole piece. The Hall IC possesses two Hall elements, which sense the magnetic profile of the ferrous target simultaneously, but at different points (spaced at a 1.5 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 compensation 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 compensation circuitry. The Hall transducers and signal processing electronics are integrated on the same silicon substrate, using a proprietary BiCMOS process.
Target Profiling
Figure 3 shows the output polarity for the orientation of target and sensor shown in figure 2. The target direction of rotation shown 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 high, ICC(High), to low ICC(Low), 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 low polarity when a tooth is the target feature nearest to the sensor. If the direction of rotation is reversed, then the output polarity inverts. Note that output voltage polarity is dependent on the position of the sense resistor, RSENSE (see figure 4).
Target Mechanical Profile
An operating device is capable of providing digital information that is representative of the mechanical features on a rotating target. The waveform diagram shown 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 sensor.
Representative Differential Magnetic Profile Sensor Electrical Output Profile, IOUT Figure 3. Output Profile of a ferrous target for the polarity indicated in figure 2.
VCC VSUPPLY
Target (Gear) Element Pitch Hall Element 2 South Pole Hall Element 1 Hall IC Pole Piece (Concentrator) Back-biasing Magnet North Pole (Pin 4 Side) Case (Pin 1 Side)
1 VCC ICC
RSENSE VOUT(H) 1 VCC
Dual-Element Hall Effect Device
ATS642
ATS642
GND 4 VOUT(L)
GND 4
Figure 1. Relative motion of the target is detected by the dual Hall elements mounted on the Hall IC.
ICC RSENSE
Rotating Target
Branded Face of Sensor
IOUT VOUT(L) VOUT(H)
I+
V+
1
4
V+
Figure 2. This left-to-right (pin 1 to pin 4) direction of target rotation results in a low 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.
Figure 4: Voltages profiles for high side and low side two-wire sensing.
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
10
ATS642LSH-DS
ATS642LSH
True Zero Speed Miniature Differential Peak-Detecting Gear Tooth Sensor
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). During calibration, the device determines the peak-topeak amplitude of the signal generated by the target. The gain of the sensor is then automatically adjusted. Figure 5 illustrates the effect of this feature.
Automatic Offset Adjust (AOA)
to compensate for offsets induced by temperature variations over time.
Digital Peak Detection
The AOA is patented circuitry that automatically compensates for 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 calibration mode and running mode, compensating for any offset drift. Continuous operation also allows it
A digital DAC tracks the internal analog voltage signal VPROC, and is used for holding the peak value of the internal analog signal. In the example shown in figure 6, the DAC would first track up with the signal and hold the upper peak's value. When VPROC drops below this peak value by BOP, the device hysteresis, the output would switch and the DAC would begin tracking the signal downward toward the negative VPROC peak. Once the DAC acquires the negative peak, the output will again switch states when VPROC is greater than the peak by the value BRP. At this point, the DAC tracks up again and the cycle repeats. The digital tracking of the differential analog signal allows the sensor to achieve true zero-speed operation.
Ferrous Target Mechanical Profile V+ Internal Differential Analog Signal
V+ Internal Differential Analog Signal Response, without AGC
AGLarge
BOP
AGSmall
BRP
V+ Internal Differential Analog Signal Response, with AGC AGSmall AGLarge
I+ Device Output Current
Figure 5. Automatic Gain Control (AGC). The AGC function corrects for variances in the air gap. Differences in the air gap affect the magnetic gradient, but AGC prevents that from affecting device performance, a shown in the lowest panel.
Figure 6: Peak Detecting Switchpoint Detail
ATS642LSH-DS
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
11
ATS642LSH
True Zero Speed Miniature Differential Peak-Detecting Gear Tooth Sensor
Power Supply Protection
Assembly Description
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.
Undervoltage Lockout
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.
Diagnostics
When the supply voltage falls below the undervoltage lockout voltage, VCC(UV), the device enters Reset, where the output state returns to the Power-On State (POS) until sufficient VCC is supplied. ICC levels may not meet datasheet limits when VCC < VCC(min).
V+
The regulated current output is configured for two-wire applications, requiring one less wire for operation than do switches with the more traditional open-collector output. Additionally, the system designer inherently gains diagnostics because there is always output current flowing, which should be in either of two narrow ranges, shown in figure 8 as ICC(High) and ICC(Low). Any current level not within these ranges indicates a fault condition. If ICC > ICC(High)max, then a short condition exists, and if ICC < ICC(low)min, then an open condition exists. Any value of ICC between the allowed ranges for ICC(High) and ICC(Low) indicates a general fault condition.
1 VCC
ATS642
CBYP 0.01 F
+mA ICC(High)max ICC(High)min ICC(Low)max Fault Short
Pins 2 and 3 floating
GND 4
A A
Open
Range for Valid ICC(HIGH)
ECU
ICC(Low)min
100 RSENSE
Range for Valid ICC(LOW)
0
Figure 7: Typical Application Circuit
Figure 8: Diagnostic Characteristics of Supply Current Values
ATS642LSH-DS
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
12
ATS642LSH
True Zero Speed Miniature Differential Peak-Detecting Gear Tooth Sensor
SENSOR OPERATION
Each operating mode is described in detail below.
Power-On
AGC is active, and selects the optimal signal gain based on the amplitude of the VPROC signal. Following each adjustment to the AGC DAC, the Offset DAC is also adjusted to ensure the internal analog signal is properly centered. During this mode, the tracking DAC is active and output switching occurs, but the duty cycle is not guaranteed to be within specification.
Running Mode
When power (VCC > VCCMIN) is applied to the device, a short period of time is required to power the various portions of the IC. During this period, the ATS642 will power-on in the high current state, ICC(High). After power on, there are conditions that could induce a change in the output state. Such an event could be caused by thermal transients, but would require a static applied magnetic field, proper signal polarity, and particular direction and magnitude of internal signal drift.
Initial Offset Adjust
The sensor intially cancels the effects of chip, magnet, and installation offsets. Once offsets have been cancelled, the digital tracking DAC is ready to track the signal and provide output switching. The period of time required for both Power-On and Initial Offset Adjust is defined as the Power-On Time.
Calibration Mode
After the Initial Calibration period, CI, establishes a signal gain, the device moves to Running mode. During Running mode, the sensor tracks the input signal and gives an output edge for every peak of the signal. AOA remains active to compensate for any offset drift over time. The ATS642 incorporates a novel algorithm for adjusting the signal gain during Running mode. This algorithm is designed to optimize the VPROC signal amplitude in instances where the magnetic signal "seen" during the calibration period is not representative of the amplitude of the magnetic signal for the installed sensor air gap (see figure 9).
The calibration mode allows the sensor to automatically select the proper signal gain and continue to adjust for offsets. The
1
2
3
4
5
BOP
Internal Differential Signal, VPROC
BOP BRP BRP
Sensor Electrical Output, IOUT
Figure 9: Operation of Running Mode Gain Adjust. Position 1. The device is initially powered-on. Self-calibration occurs. Position 2. Small amplitude oscillation of the target sends an erroneously small differential signal to the sensor. The amplitude of VPROC is greater than the switching hysteresis (BOP and BRP), and the device output switches. Position 3. The calibration period completes on the third rising output edge, and the device enters Running mode. Position 4. True target rotation occurs and the correct magnetic signal is generated for the installation air gap. The established signal gain is too large for the target's rotational magnetic signal at the given air gap. Position 5. Running Mode Calibration corrects the signal gain to an optimal level for the installation air gap.
ATS642LSH-DS
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
13
ATS642LSH
True Zero Speed Miniature Differential Peak-Detecting Gear Tooth Sensor
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 T = PD x RJA TJ = TA + T (1) (2) (3)
Example: Reliability for VCC at TA = 150C, package SH (I1 trim), 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.
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.
ATS642LSH-DS
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
14
ATS642LSH
True Zero Speed Miniature Differential Peak-Detecting Gear Tooth Sensor
Package SH Module
5.5 .217
E 0.75 .0295 E 0.75 .0295
0.43 .017
C B
8.0
.315
5.8
.228
E
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 E Hall elements (2X) not to scale; controlling dimension inches
ATS642LSH-DS
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
15
ATS642LSH
True Zero Speed Miniature Differential Peak-Detecting Gear Tooth Sensor
The products described herein are manufactured under one or more of the following U.S. patents: 5,045,920; 5,264,783; 5,442,283; 5,389,889; 5,581,179; 5,517,112; 5,619,137; 5,621,319; 5,650,719; 5,686,894; 5,694,038; 5,729,130; 5,917,320; and other patents pending. Allegro MicroSystems, Inc. reserves the right to make, from time to time, such departures from the detail specifications as may be required to permit improvements in the performance, reliability, or manufacturability of its products. Before placing an order, the user is cautioned to verify that the information being relied upon is current. Allegro products are not authorized for use as critical components in life-support devices or systems without express written approval. The information included herein is believed to be accurate and reliable. However, Allegro MicroSystems, Inc. assumes no responsibility for its use; nor for any infringement of patents or other rights of third parties which may result from its use. Copyright (c) 2004, 2005 Allegro MicroSystems, Inc.
ATS642LSH-DS
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
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