Engineering samples available on a limited basis. Contact your local
sales or applications support office for additional information.
Description
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 obtain-
ATS642LSH-DS, Rev. 1
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 × 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
Two-Wire True Zero Speed Miniature Differential
Peak-Detecting Gear Tooth Sensor with Continuous Calibration
Continued on the next page…
Package: 4-pin Module (suffix SH)
Functional Block Diagram
Not to scale
ATS642LSH
VCC
Automatic Offset
Control AOA DAC
Hall
Amplifier
AGC DAC
Gain
Tracking
DAC Peak Hold
Gain Control
Internal Regulator
Test Signals
GND
Test
Two-Wire True Zero Speed Miniature Differential
Peak-Detecting Gear Tooth Sensor with Continuous Calibration
ATS642LSH
2
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Absolute Maximum Ratings
Characteristic Symbol Notes Rating Unit
Supply Voltage VCC 28 V
Reverse_Supply Voltage VRCC –18 V
Operating Ambient Temperature TARange L –40 to 150 ºC
Maximum Junction Temperature TJ(max) 165 ºC
Storage Temperature Tstg –65 to 170 ºC
Selection Guide
Part Number ICC Typical Packing*
ATS642LSHTN-I1-T 6.0 Low to 14.0 High mA Tape and reel, 13-inch reel 800 pieces/reel
ATS642LSHTN-I2-T 7.0 Low to 14.0 High mA
*Contact Allegro® for additional packing options
ing 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.
Description (continued)
Pin-out Diagram Terminal List
Number Name Function
1 VCC Connects power supply to chip
2 NC No connection
3 Test pin Float or tie to GND
4 GND Ground terminal
2431
Two-Wire True Zero Speed Miniature Differential
Peak-Detecting Gear Tooth Sensor with Continuous Calibration
ATS642LSH
3
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
OPERATING CHARACTERISTICS using reference target 60-0, TA and VCC within specification, unless otherwise noted
Characteristic Symbol Test Conditions Min. Typ.1Max. Units
ELECTRICAL CHARACTERISTICS
Supply Voltage2VCC Operating; TJ < 165 °C 4.0 – 24 V
Undervoltage Lockout VCC(UV) VCC 0 → 5 V and 5 → 0 V – – 4.0 V
Supply Zener Clamp Voltage VZICC = ICC(max) + 3 mA; TA = 25°C 28 – – V
Supply Zener Current IZTest conditions only; VZ = 28 V – – ICC(max)+
3 mA mA
Supply Current
ICC(Low)
ATS642LSH-I1 4.0 6.0 8.0 mA
ATS642LSH-I2 5.9 7.0 8.4 mA
ICC(High)
ATS642LSH-I1 12.0 14.0 16.0 mA
ATS642LSH-I2 11.8 14.0 16.8 mA
Supply Current Ratio ICC(High)/
ICC(Low)
Ratio of high current to low current 1.85 – 3.05 –
Reverse Battery Current IRCC VRCC = –18 V – – –5 mA
POWER-ON STATE CHARACTERISTICS
Power-On State3POS t > tPO –I
CC(High) ––
Power-On Time4tPO Target gear speed < 100 rpm – 1 2 ms
OUTPUT STAGE
Output Slew Rate5dI/dt RLOAD = 100 Ω, CLOAD = 10 pF – 10 – mA/μs
Continued on the next page.
Two-W ire True Zero Speed Miniature Dif ferential
Peak-Detecting Gear Tooth Sensor with Continuous Calibration
ATS642LSH
4
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
OPERATING CHARACTERISTICS (continued) using reference target 60-0, TA and VCC within specification, unless otherwise noted
Characteristic Symbol Test Conditions Min. Typ.1Max. Units
SWITCHPOINT CHARACTERISTICS
Rotation Speed SROT Reference Target 60-0 0 – 8,000 rpm
Analog Signal Bandwidth BW Equivalent to f – 3 dB 20 40 – kHz
Operate Point BOP
Transitioning from ICC(High) to ICC(Low); positive peak
referenced; AG < AGMAX
– 120 – mV
Release Point BRP
Transitioning from ICC(Low) to ICC(High); negative peak
referenced; AG < AGMAX
– 120 – mV
CALIBRATION
Initial Calibration CI
Quantity of rising output (current) edges required for
accurate edge detection – – 3 Edge
DAC CHARACTERISTICS
Allowable User-Induced Differential
Offset
Output switching only; may not meet datasheet speci-
fi cations – ±60 – G
FUNCTIONAL CHARACTERISTICS6
Operational Air Gap Range7AG ∆DC within specification 0.5 – 2.75 mm
Maximum Operational Air Gap
Range AGOP(max)
Output switching (no missed edges); ∆DC not guaran-
teed ––3mm
Duty Cycle Variation ∆DC Wobble < 0.5 mm; Typical value at AG = 1.5 mm, for
max., min., AG within specification 41 – 61 %
Duty Cycle Pitch Variance8EDC AG = 1.5 mm – ±1.5 – %
Operating Signal Range9Sig Operating within specification 30 – 1000 G
Minimum Operating Signal SigOP(min)
Output switching (no missed edges); ∆DC not guaran-
teed 20 – – G
1Typical values are at TA = 25°C and VCC = 12 V. Performance may vary for individual units, within the specified maximum and minimum limits.
2Maximum 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 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.
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 char-
acterized. The field available from the reference target is given in the reference target parameter section of the datasheet.
8EDC 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.
Two-W ire True Zero Speed Miniature Dif ferential
Peak-Detecting Gear Tooth Sensor with Continuous Calibration
ATS642LSH
5
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
REFERENCE TARGET, 60-0 (60 Tooth Target)
Characteristics Symbol Test Conditions Typ. Units Symbol Key
Outside Diameter DoOutside diameter of target 120 mm Doht
F
Air Gap
Branded Face of Sensor
t
tv
Face Width F Breadth of tooth, with
respect to sensor 6mm
Angular Tooth Thickness t Length of tooth, with
respect to sensor 3 deg
Angular Valley Thickness tv
Length of valley, with
respect to sensor 3 deg
Tooth Whole Depth ht3mm
Material Low Carbon Steel – –
Reference Gear Magnetic Gradient Amplitude
With Reference to Air Gap
Air Gap (mm)
Peak-to-Peak Differential B (G)
0
100
200
300
400
500
600
700
800
11.520.5 2.5 3
Reference Gear Magnetic Profile
Two Tooth-to-Valley Transitions
-500
-400
-300
-200
-100
0
100
200
300
400
500
Gear Rotation (°)
Differential B* (G)
024681012
0.50
(mm)
Air Gap
0.50 mm AG
3.00 mm AG
0.75
1.00
1.25
1.50
1.75
2.00
2.25
2.50
2.75
3.00
Reference Target
60-0
of Sensor
Branded Face
Two-W ire True Zero Speed Miniature Dif ferential
Peak-Detecting Gear Tooth Sensor with Continuous Calibration
ATS642LSH
6
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Characteristic Data
I1 Trim
Supply Current (High) versus Am bient Temperat ur e
(ATS642-I1)
12
13
14
15
16
-50 0 50 100 150
T
A
(°C)
I
CC(HIGH)
(mA)
VCC (V)
24
12
4
S upply Curren t (High) ve rsus Supply Voltage
(ATS642-I1)
12
13
14
15
16
0 5 10 15 20 25
V
CC
(V)
I
CC(HIGH)
(mA)
T
A
(°C)
Supply Current (Low) versus Ambient Temperature
(ATS642- I1)
4
5
6
7
8
-50 0 50 100 150
T
A
(°C)
ICC(LOW) (mA)
Vcc (V)
24
12
4
Supply Current (Low) versus Supply Volta ge
(ATS642-I1)
4
5
6
7
8
0510152025
V
CC
(V)
I
CC(LOW)
(mA)
T
A
(°C)
-40
25
150
-40
25
85
150
Two-W ire True Zero Speed Miniature Dif ferential
Peak-Detecting Gear Tooth Sensor with Continuous Calibration
ATS642LSH
7
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Duty Cycle versus Air Gap*
43
45
47
49
51
53
55
57
59
61
41
0.51.01.52.02.53.0
AG (mm)
DC (%)
TA (°C)
-40
25
150
Duty Cycl e versus Ambie nt Tempera t ure
43
45
47
49
51
53
55
57
59
61
41
–50 0 50 100 150
T
A
(°C)
DC (%)
AG ( mm)
0.5
1.5
2.75
Duty Cycle Variance versus Air Gap
Mean ± 3 Sigma, 25°C
-6
-4
-2
0
2
4
6
0.5 1.0 1.5 2.0 2.5 3.0
AG (mm)
E
DC
(%)
*The trend of duty cycle versus air gap is driven by the actual magnetic profile of the
target (see figure on page 5).
Two-W ire True Zero Speed Miniature Dif ferential
Peak-Detecting Gear Tooth Sensor with Continuous Calibration
ATS642LSH
8
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
ΔTEAGIN (mm)
ΔTEAGOUT (mm)
Allowable Air Gap Movement from TEAGCAL
-0.2
0
0.2
0.4
0.6
0.8
1.0
1.2
0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8
Characteristic Allowable Air Gap Movement
60-0 (60 Tooth Target)
The colored area in the chart above shows the region of allow-
able 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 move-
ment, and may not always be within specification throughout the
entire operating region (to AG(OPmax)).
The axis parameters for the chart are defined in the draw-
ings 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.
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.
TEAGIN
Sensor
Sensor
TEAGOUT
(a)
Sensor TEAGCAL
(b) (c)
Two-W ire True Zero Speed Miniature Dif ferential
Peak-Detecting Gear Tooth Sensor with Continuous Calibration
ATS642LSH
9
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
THERMAL CHARACTERISTICS may require derating at maximum conditions, see application information
Characteristic Symbol Test Conditions* Value Units
Package Thermal Resistance RθJA
Single-layer PCB with copper limited to solder pads 126 ºC/W
Two-layer PCB with 3.8 in.2 of copper area on each side con-
nected with thermal vias and to device ground pin 84 ºC/W
*Additional information is available on the Allegro Web site.
6
7
8
9
2
3
4
5
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
20 40 60 80 100 120 140 160 180
Temperature (ºC)
Maximum Allowable V
CC
(V)
Power Derating Curve
(R
θJA
= 126 ºC/W)
(R
θJA
= 84 ºC/W)
VCC(min)
VCC(max)
0
100
200
300
400
500
600
700
800
900
1000
1100
1200
1300
1400
1500
1600
1700
1800
1900
20 40 60 80 100 120 140 160 180
Temperature (°C)
Power Dissipation, P
D
(mW)
Maximum Power Dissipation, PD(max)
(R
θJA
= 126 ºC/W)
(RθJA = 84 ºC/W)
Two-W ire True Zero Speed Miniature Dif ferential
Peak-Detecting Gear Tooth Sensor with Continuous Calibration
ATS642LSH
10
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Sensing Technology
The gear tooth sensor subassembly contains a single-chip dif-
ferential 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 process-
ing electronics are integrated on the same silicon substrate, using
a proprietary BiCMOS process.
Target Profiling
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.
Output Polarity
Figure 3 shows the output polarity for the orientation of target
and sensor shown in figure 2. The target direction of rota-
tion 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 rota-
tion 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 (Gear)
Back-biasing Magnet
South Pole
North Pole Case
(Pin 1 Side)(Pin 4 Side)
Hall IC
Pole Piece
Element Pitch
(Concentrator)
Dual-Element
Hall Effect Device
Hall Element 1
Hall Element 2
of Sensor
Rotating Target Branded Face
14
Functional Description
Figure 1. Relative motion of the target is detected by the dual Hall ele-
ments mounted on the Hall IC.
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) rota-
tion inverts the output signal polarity. Figure 4: Voltages profiles for high side and low side two-wire sensing.
Figure 3. Output Profile of a ferrous target for the polarity indicated in
figure 2.
ATS642
VCC
GND
VCC
ICC
1
4
VOUT(L)
ATS642
VCC
GND
VSUPPLY
1
4
VOUT(H)
ICC
RSENSE
RSENSE
I
OUT
V
OUT(H)
V+
V
OUT(L)
V+
I+
Representative
Differential
Magnetic Profile
Target
Mechanical Profile
Sensor Electrical
Output Profile, I
OUT
Two-W ire True Zero Speed Miniature Dif ferential
Peak-Detecting Gear Tooth Sensor with Continuous Calibration
ATS642LSH
11
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
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 speci-
fication). During calibration, 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 5 illustrates the
effect of this feature.
Automatic Offset Adjust (AOA)
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 Operat-
ing Characteristics table.) This circuitry is continuously active,
including both during calibration mode and running mode, com-
pensating for any offset drift. Continuous operation also allows it
to compensate for offsets induced by temperature variations over
time.
Digital Peak Detection
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 hyster-
esis, 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.
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.
Mechanical Profile
AG
Small
AG
Large
AG
Small
AG
Large
Internal Differential
Analog Signal
Response, with AGC
Internal Differential
Analog Signal
Response, without AGC
Ferrous Target
V+
V+
Figure 6: Peak Detecting Switchpoint Detail
Device
Output Current
B
RP
Internal
Differential
Analog Signal
V+
I+
B
OP
Two-W ire True Zero Speed Miniature Dif ferential
Peak-Detecting Gear Tooth Sensor with Continuous Calibration
ATS642LSH
12
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
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 pro-
tection 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
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 sup-
plied. ICC levels may not meet datasheet limits when
VCC < VCC(min).
Assembly Description
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
The regulated current output is configured for two-wire appli-
cations, 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 condi-
tion. 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.
Figure 7: Typical Application Circuit
ATS642
VCC
GND
V+
0.01
1
4
µF
ECU
Pins 2 and 3 floating
R
100 Ω
SENSE
CBYP
Figure 8: Diagnostic Characteristics of Supply Current Values
ICC(High)max
ICC(High)min Range for Valid ICC(HIGH)
Range for Valid ICC(LOW)
ICC(Low)max
ICC(Low)min
0
+mA
Short
Fault
Open
Two-W ire True Zero Speed Miniature Dif ferential
Peak-Detecting Gear Tooth Sensor with Continuous Calibration
ATS642LSH
13
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Sensor Operation
Each operating mode is described in detail below.
Power-On
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
The calibration mode allows the sensor to automatically select
the proper signal gain and continue to adjust for offsets. The
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 switch-
ing occurs, but the duty cycle is not guaranteed to be within
specification.
Running 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 repre-
sentative of the amplitude of the magnetic signal for the installed
sensor air gap (see figure 9).
Sensor Electrical
Output, I
OUT
Internal Differential
Signal, V
PROC
B
RP
B
OP
B
OP
B
RP
1 2 3 4 5
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 ampli-
tude 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 estab-
lished 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.
Two-W ire True Zero Speed Miniature Dif ferential
Peak-Detecting Gear Tooth Sensor with Continuous Calibration
ATS642LSH
14
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
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 sup-
plied 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 sum-
marizing 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 × IIN (1)
T = PD × RJA (2)
TJ = TA + ΔT (3)
For example, given common conditions such as: TA= 25°C,
VCC = 12 V, ICC = 4 mA, and RJA = 140 °C/W, then:
P
D = VCC × ICC = 12 V × 4 mA = 48 mW
T = PD × RJA = 48 mW × 140 °C/W = 7°C
T
J = TA + T = 25°C + 7°C = 32°C
A worst-case estimate, PD(max), represents the maximum allow-
able power level (VCC(max), ICC(max)), without exceeding TJ(max),
at a selected RJA and TA.
Example: Reliability for VCC at TA =
150°C, package SH
(I1 trim), using minimum-K PCB
Observe the worst-case ratings for the device, specifically:
RJA
=
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 ÷ RJA = 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 reli-
able 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.
Two-W ire True Zero Speed Miniature Dif ferential
Peak-Detecting Gear Tooth Sensor with Continuous Calibration
ATS642LSH
15
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Package SH Module
0.71±0.05
5.00±0.10 4.00±0.10
1.00±0.10
0.60±0.10
24.65±0.10
13.10±0.10
1.0 REF
0.71±0.10 0.71±0.10
1.60±0.10
1.27±0.10
5.50±0.10
5.50±0.05
8.00±0.05
5.80±0.05
1.70±0.10
243
1A
A
B
D
For Reference Only, not for tooling use (reference DWG-9003)
Dimensions in millimeters
A
B
C
C
D
Dambar removal protrusion (16X)
Metallic protrusion, electrically connected to pin 4 and substrate (both sides)
Thermoplastic Molded Lead Bar for alignment during shipment
Active Area Depth 0.43 mm REF
Branded
Face
Standard Branding Reference View
= 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
LLLLLLL
YYWW
NNN
Branding scale and appearance at supplier discretion
0.38 +0.06
–0.04
F
E
F
FE
0.75
E2E1
0.75
Hall elements (E1, E2); not to scale
Two-W ire True Zero Speed Miniature Dif ferential
Peak-Detecting Gear Tooth Sensor with Continuous Calibration
ATS642LSH
16
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Copyright ©2004-2009, Allegro MicroSystems, Inc.
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 de par tures from the detail spec i fi ca tions as may be required to per-
mit improvements in the per for mance, 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 in for ma tion in clud ed herein is believed to be ac cu rate and reliable. How ev er, Allegro MicroSystems, Inc. assumes no re spon si bil i ty for its use;
nor for any in fringe ment 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
