Allegro AATS643LSH Self-calibrating, zero-speed differential gear tooth sensor with continuous update Datasheet

ATS643LSH
Self-Calibrating, Zero-Speed Differential
Gear Tooth Sensor with Continuous Update
Features and Benefits
Description
▪
▪
▪
▪
▪
▪
▪
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.
Fully-optimized differential digital gear tooth sensor
Single chip-IC for high reliability
Internal current regulator for 2-wire operation
Small mechanical size (8 mm diameter x 5.5 mm depth)
Switchpoints air gap independent
Digital output representing gear profile
Precise duty cycle accuracy throughout temperature
range
▪ Large operating air gaps
▪ <2 ms power-on time
Continued on the next page…
Packages: 4 pin SIP (suffix SH)
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 finetune the switchpoints while in running mode, maintaining
Continued on the next page…
Not to scale
Functional Block Diagram
VCC (Pin 1)
Hall AMP
Offset Adjust
AGC
Internal
Regulator
PDAC
ThresholdP
Reference
Generator
and Updates
Threshold
Logic
ThresholdN
NDAC
ATS643-DS, Rev. 2
GND (Pin 4)
Self-Calibrating, Zero-Speed Differential
Gear Tooth Sensor with Continuous Update
ATS643LSH
Features and Benefits (continued)
▪ AGC and reference adjust circuit
▪ True zero-speed operation
▪ Undervoltage lockout
▪ Wide operating voltage range
▪ Defined power-on state
Description (continued)
the device specifications even through large changes in air gap
or temperature.
The regulated current output is configured for two-wire operation,
offering inherent diagnostic information. This device is ideal for
obtaining speed and duty cycle information in gear-tooth based
applications such as transmission speed sensing.
Part Number
Pb-free1
Packing2
ICC Typical
ATS643LSHTN-I1-T
Yes
Tape and Reel 13-in. 800 pcs./reel
6.0 Low to 14.0 High mA
ATS643LSHTN-I2-T
Yes
Tape and Reel 13-in. 800 pcs./reel
7.0 Low to 14.0 High mA
1Pb-based
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:
ATS643LSHTN-I1 and ATS643LSHTN-I2.
2Contact Allegro for additional packing options.
3Some restrictions may apply to certain types of sales. Contact Allegro for details.
Absolute Maximum Ratings
Characteristic
Symbol
Supply Voltage
VCC
Reverse-Supply Voltage
VRCC
Notes
See Power Derating section
Rating
Units
–
–
–18
V
Operating Ambient Temperature
TA
–40 to 150
ºC
Maximum Junction Temperature
TJ(max)
165
ºC
Tstg
–65 to 170
ºC
Storage Temperature
Pin-out Diagram
Range L
Terminal List
Name
VCC
1 2 3 4
Description
Number
Connects power supply to chip
1
NC
No connection. Float or tie to VCC
2
TEST
For Allegro use, float or tie to GND
3
GND
Ground terminal
4
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
2
Self-Calibrating, Zero-Speed Differential
Gear Tooth Sensor with Continuous Update
ATS643LSH
OPERATING CHARACTERISTICS using reference target 60-0, TA and VCC within specification, unless otherwise noted
Characteristic
Symbol
Test Conditions
Min.
Typ.
Max.
Units
4.0
–
24
V
VCC 0 → 5 V
–
3.5
4.0
V
ICC = 19 mA for ATS643-I1, and 19.8 mA for
ATS643-I2; TA = 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.
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
3
Self-Calibrating, Zero-Speed Differential
Gear Tooth Sensor with Continuous Update
ATS643LSH
OPERATING CHARACTERISTICS (continued) using reference target 60-0, TA and VCC within specification, unless otherwise noted
Characteristic
Symbol
Test Conditions
Min.
Typ.
Max.
Units
Reference Target 60-0
0
–
12,000
rpm
Equivalent to f – 3dB
25
40
–
kHz
SWITCHPOINT CHARACTERISTICS
Rotation Speed
SROT
Bandwidth
BW
Operate Point
BOP
% of peak to peak referenced from PDAC to NDAC,
AG < AGMAX
–
65
–
%
Release Point
BRP
% of peak to peak referenced from PDAC to NDAC,
AG < AGMAX
–
35
–
%
–
–
3
Edge
–
–
3
Edge
–
175
–
mV
–
±60
–
G
–
9
–
Bit
CALIBRATION3
Initial Calibration Period
CI
AGC Calibration Disable
Cf
Start Mode Hysteresis
Quantity of rising output (current) edges required for
accurate edge detection
Quantity of rising output (current) edges used for
calibrating AGC
POHYS
DAC CHARACTERISTICS
Dynamic Offset Cancellation
Quantity of bits available for PDAC/NDAC tracking of
both positive and negative signal peaks
Tracking Data Resolution
FUNCTIONAL CHARACTERISTICS
Air Gap Range4
Maximum Operable Air Gap
AG
AG(opmax)
Duty Cycle Variation
ΔDC
Input Signal Range
Sig
Minimum Operable Input Signal
Sig(opmin)
ΔDC within specification
0.5
–
2.5
mm
Output switching (no missed edges); ΔDC not
guaranteed
–
–
2.75
mm
Wobble < 0.5 mm, AG within specification
–
–
±10
%
ΔDC within specification
40
–
1400
G
Output switching (no missed edges); ΔDC not
guaranteed
30
–
–
G
1Power-On
Time includes the time required to complete the internal automatic offset adjust. The DACs are then ready for peak acquisition.
is the difference between 10% of ICC(Low) and 90% of ICC(High) , and dt is time period between those two points. Note: dI/dt is dependent upon the value
of the bypass capacitor, if one is used.
3Continuous Update (calibration) functions continuously during Running mode operation.
4AG is dependent on the available magnetic field. The available field is dependent on target geometry and material, and should be independently
characterized. The field available from the reference target is given in the reference target parameter section of the datasheet.
2dI
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
4
Self-Calibrating, Zero-Speed Differential
Gear Tooth Sensor with Continuous Update
ATS643LSH
REFERENCE TARGET, 60-0 (60 Tooth Target)
Characteristics
Symbol
Test Conditions
Typ.
Units
120
mm
Outside Diameter
Do
Outside diameter of target
Face Width
F
Breadth of tooth, with respect
to 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).
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
5
Self-Calibrating, Zero-Speed Differential
Gear Tooth Sensor with Continuous Update
ATS643LSH
Characteristic Data
Data taken from 3 lots, 30 pieces/lot; I1 trim
Reference Target 60-0
Duty Cycle at 1000 RPM
Duty Cycle at 1000 RPM
60
60
AG (mm)
Duty Cycle (%)
50
Duty Cycle (%)
3.0
2.75
2.5
2.25
2.0
1.5
1.0
0.5
55
45
40
–50
55
50
TA (ºC)
-40
0
25
85
150
45
0
50
100
150
200
40
0
0.5
1
1.5
TA (°C)
2
2.5
3
3.5
AG (mm)
Duty Cycle (25°C)
60
Duty Cycle (%)
AG (mm)
3.0
2.75
2.5
2.25
2.0
1.5
1.0
0.5
55
50
45
40
0
500
1000
1500
2000
2500
RPM
Continued on the next page.
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
6
Self-Calibrating, Zero-Speed Differential
Gear Tooth Sensor with Continuous Update
ATS643LSH
Characteristic Data (continued)
Data taken from 3 lots, 30 pieces/lot; I1 trim
ICC (Low)
ICC(Low)
9
26.5
20.0
12.0
4.0
8
TA (ºC)
7
6
7
6
5
5
4
4
3
–50
3
0
50
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
50
100
150
11
200
0
5
10
TA (°C)
20
25
30
Hysteresis of ΔIICC
Switching Due to ΔB
Switch to Low
Switch to High
ICC(High)
ICC(Low)
BRP
BOP
I+
Output current in relation to sensed magnetic flux density. Transition through BOP
must precede by transition through BRP.
15
Vcc (V)
ICC
0
150
85
25
0
–40
16
15
11
–50
30
Vcc (V)
TA (°C)
B+
BHYS
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
7
Self-Calibrating, Zero-Speed Differential
Gear Tooth Sensor with Continuous Update
ATS643LSH
THERMAL CHARACTERISTICS may require derating at maximum conditions, see application information
Characteristic
Symbol
Test Conditions
Min.
Minimum-K PCB (single-sided with copper limited to
126
solder pads)
Low-K PCB (single-sided with copper limited to solder
84
pads and 3.57 in.2 (23.03 cm2) of copper area)
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
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
8
Self-Calibrating, Zero-Speed Differential
Gear Tooth Sensor with Continuous Update
ATS643LSH
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
Target (Gear)
Determining Output Signal Polarity. In figure 3, the top
panel, labeled Mechanical Position, represents the mechanical features of the target gear and orientation to the device. The
bottom panel, labeled 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)
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.
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
9
Self-Calibrating, Zero-Speed Differential
Gear Tooth Sensor with Continuous Update
ATS643LSH
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
(A) TEAG varying; cases such as
eccentric mount, out-of-round region,
normal operation position shift
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.
(B) Internal analog signal, VPROC,
typically resulting in the sensor
V+
Smaller
TEAG
Sensor
Target
Smaller
TEAG
Hysteresis Band
(Delimited by switchpoints)
Larger
TEAG
Sensor
Larger
TEAG
VPROC (V)
Target
Smaller
TEAG
0
360
Target Rotation (°)
(C) Referencing the internal analog signal, VPROC, to continuously update device response
1
2
3
4
Determinant
Peak Values
BOP(#1)
BRP(#1)
Pk(#1), Pk(#2)
Pk(#2), Pk(#3)
BOP(#2)
BRP(#2)
Pk(#3), Pk(#4)
Pk(#4), Pk(#5)
BOP(#3)
BRP(#3)
Pk(#5), Pk(#6)
Pk(#6), Pk(#7)
BOP(#4)
Pk(#7), Pk(#8)
BRP(#4)
Pk(#8), Pk(#9)
V+
Pk(#9)
Pk(#1)
Pk(#3)
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
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
Self-Calibrating, Zero-Speed Differential
Gear Tooth Sensor with Continuous Update
ATS643LSH
Power-On State Operation. The ATS643 is guaranteed to
power-on in the high current state, ICC(High).
Initial Edge Detection. The device self-calibrates using the
initial teeth sensed, and then enters Running mode. This results
in reduced accuracy for a brief period (less than four teeth),
however, it allows the device to optimize for continuous update
yielding adaptive sensing during Running mode. As shown in
figure 5, the first three high peak signals are used to calibrate
AGC. However, there is a slight variance in the duration of initialization, depending on what target feature is nearest the 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
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
Self-Calibrating, Zero-Speed Differential
Gear Tooth Sensor with Continuous Update
ATS643LSH
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
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
Self-Calibrating, Zero-Speed Differential
Gear Tooth Sensor with Continuous Update
ATS643LSH
Undervoltage Lockout. When the supply voltage falls
below the minimum operating voltage, VCC(UV), ICC goes high
and remains high regardless of the state of the magnetic gradient from the target. This lockout feature prevents false signals,
caused by undervoltage conditions, from propagating to the
output of the 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
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
ATS643LSH
Self-Calibrating, Zero-Speed Differential
Gear Tooth Sensor 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)
ΔT = PD × RθJA
(2)
TJ = TA + ΔT
(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:
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 ÷ 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
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 (VCC(max), ICC(max)), without exceeding TJ(max),
at a selected RθJA and TA.
14
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
Self-Calibrating, Zero-Speed Differential
Gear Tooth Sensor with Continuous Update
ATS643LSH
Package SH, 4-pin SIP
5.5 .217
B
8.0
5.8
.228
5.0
.244
4.0
.315
.157
1.7
.067
0.38 .015
A
1
2
3
4
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
15
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
ATS643LSH
Self-Calibrating, Zero-Speed Differential
Gear Tooth Sensor 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, 2006 Allegro MicroSystems, Inc.
16
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com