Allegro ATS617LSGTN-T Dynamic, self-calibrating, peak-detecting, differential hall effect gear tooth sensor ic Datasheet

ATS617LSG
Dynamic, Self-Calibrating, Peak-Detecting, Differential
Hall Effect Gear Tooth Sensor IC
Features and Benefits
Description
▪ Self-calibrating for tight timing accuracy
▪ First-tooth detection
▪ Immunity to air gap variation and system offsets
▪ Immunity to signature tooth offsets
▪ Integrated capacitor provides analog peak and
valley information
▪ Low timing-accuracy drift with temperature changes
▪ Low radiated emissions
▪ Integrated, series resistor on VCC pin for improved
transient immunity
▪ Large air gap capability
▪ Small, integrated package
▪ Optimized magnetic circuit
▪ Undervoltage lockout (UVLO)
▪ Wide operating voltage range
The ATS617 gear-tooth sensor IC is a peak-detecting device
that uses automatic gain control and an integrated capacitor
to provide extremely accurate gear edge detection down to
low operating speeds. Each device consists of a high-temperature plastic shell that holds together a samarium-cobalt
pellet, a pole piece, and a differential open-collector Hall IC
that has been optimized to the magnetic circuit. This small
package can be easily assembled and used in conjunction
with a wide variety of gear shapes and sizes.
The technology used for this device is Hall-effect based. The
device incorporates a dual-element Hall IC that switches in
response to differential magnetic signals created by ferromagnetic targets. The sophisticated processing circuitry
contains an A-to-D converter that self-calibrates (normalizes) the internal gain of the device to minimize the effect of
air gap variations. The patented peak-detecting filter circuit
provides immunity to magnet and system offsets and has the
ability to discriminate relatively fast changes such as those
caused by tilt, gear wobble, and eccentricities. This easy-tointegrate solution provides first falling edge detection and
stable operation to extremely low rpm. The ATS617 can be
used as a replacement for the ATS616.
Package: 4-pin SIP (suffix SG)
The ATS617 is ideal for use in systems that gather speed,
position, and timing information using gear-tooth-based
Continued on the next page…
Not to scale
Functional Block Diagram
VCC
RS
Voltage
Regulator
Power-On
Logic
UVLO
Tooth and Valley
Comparator
VOUT
Hall
Amp
Gain
Track and
Hold
Current
Limit
Reference
Generator
Hall
Amp
Track and
Hold
GND
TEST
(Recommended)
ATS617LSG-DS, Rev. 1
ATS617LSG
Dynamic, Self-Calibrating, Peak-Detecting, Differential
Hall Effect Gear Tooth Sensor IC
Description (continued)
configurations. This device is particularly suited to those applications that require extremely accurate duty cycle control or
accurate edge-detection, such as automotive camshaft sensing.
The ATS617 is provided in a 4-pin SIP that is Pb (lead) free,
with a 100% matte tin plated leadframe.
Selection Guide
Part Number
Packing*
ATS617LSGTN-T
13-in. reel, 800 pieces/reel
*Contact Allegro® for additional packing options
Absolute Maximum Ratings
Characteristic
Symbol
Notes
Unit
Supply Voltage
VCC
26.5
V
Reverse Supply Voltage
VRCC
–18
V
Output Off Voltage
See Power Derating section
Rating
VOUTOFF
24
V
Continuous Output Current
IOUT
25
mA
Reverse Output Current
IROUT
50
mA
–40 to 150
ºC
TJ(max)
165
ºC
Tstg
–65 to 170
ºC
Operating Ambient Temperature
TA
Maximum Junction Temperature
Storage Temperature
Range L
Pin-out Diagram
Terminal List
1
2
3
4
Number
Name
Function
1
VCC
Device supply
2
VOUT
Device output
3
Test
Tie to GND, or float
4
GND
Device ground
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
2
ATS617LSG
Dynamic, Self-Calibrating, Peak-Detecting, Differential
Hall Effect Gear Tooth Sensor IC
OPERATING CHARACTERISTICS over operating voltage and temperature range, unless otherwise noted
Characteristic
Symbol
Test Condition
Min.
Typ.1
Max.
Unit
4.5
–
24
V
–
60
72
Ω
–
3.7
–
V
–
100
400
mV
Electrical Characteristics
Supply Voltage2
VCC
Supply Protection Resistor
RS
Undervoltage Lockout Threshold
Output On Voltage
VCC(UV)
Operating, TJ < 165C
VCC = 0 → 5 V; VCC = 5 → 0 V
VOUT(SAT) IOUT = 15 mA, output on
Supply Zener Clamp Voltage
VZsupply
ICC = 15 mA, TA = 25°C
28
–
–
V
Output Zener Clamp Voltage
VZoutput
IOUT = 3 mA, TA = 25°C
30
–
–
V
Supply Zener Current
IZsupply
VS = 28 V
–
–
15
mA
Output Zener Current
IZoutput
VOUT = 30 V
–
–
3
mA
Output Current Limit
IOUTM
VOUT = 12 V
25
45
55
mA
VOUT = 24 V, output off
–
–
15
μA
Output Leakage Current
IOUTOFF
Supply Current
ICC
VCC > VCC(min)
3
6
12
mA
Power-On Time
tPO
VCC > 5 V
–
80
500
μs
Power-On State
POS
VCC = 0 → 5 V
–
High
–
V
RPU = 2 kΩ, CL = 4.7 nF, 10% to 90%
–
21
–
μs
VPU = 5 V, RPU = 2 kΩ, CL = 4.7 nF, 90% to 10%
–
6
–
μs
VPU =12 V, RPU = 2 kΩ, CL = 4.7 nF, 90% to 10%
6
9
12
μs
Allegro reference target 60+2 operating at or above Minimum Operating Speed
0.4
–
2.5
mm
Operation at or above Minimum Operating Speed
60
–
–
G
–
15
–
kHz
10
–
–
rpm
Output Rise Time3
tr
Output Fall Time
tf
Performance Characteristics
Operating Air Gap Range
Operating Magnetic Flux Density
Differential4
AG
BAG(p-p)
Analog Signal Bandwidth
BW
Minimum Operating Speed
SOP
Allegro 60+2 reference target
Continued on the next page…
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
3
ATS617LSG
Dynamic, Self-Calibrating, Peak-Detecting, Differential
Hall Effect Gear Tooth Sensor IC
OPERATING CHARACTERISTICS (continued) over operating voltage and temperature range, unless otherwise noted
Symbol
Test Condition
Min.
Typ.1
Max.
Unit
Initial Calibration Cycle5
ncal
Output edges before calibration is completed, at fsig < 100 Hz
–
1
–
edge
Calibration Mode Disable
ndis
Output falling edges for startup calibration to be complete
64
64
64
edge
Relative Timing Accuracy, Sequential6,7
Eθ
Target Speed = 1000 rpm, BAG(p-p) > 100 G
–
±0.5
±0.75
deg.
Target Speed = 1000 rpm, BAG(p-p) > 60 G
–
–
±1.5
deg.
Output switching only; may not meet data sheet specifications
–
–
±50
G
Characteristic
Performance Characteristics (continued)
Allowable User Induced Differential Offset4
∆BApp
Switching Hysteresis, Start-up
VSWHYS(su)
–
190
–
mV
Switching Hysteresis, Running Mode
VSWHYS(rm)
–
105
–
mV
1 Typical
data is at VCC = 12 V and TA = 25°C. Performance may vary for individual units, within the specified maximum and minimum limits.
Maximum voltage must be adjusted for power dissipation and junction temperature; see Power Derating section.
3 This performance is not affected by the design of the ATS617, it is determined only by the external interface circuitry.
4 1 G (gauss) = 0.1 mT (millitesla), exactly.
5 Non-uniform magnetic profiles may require additional edges before calibration is complete.
6 For Allegro 60+2 reference target.
7 Accuracy may be compromised during the calibration cycle.
2
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
4
Dynamic, Self-Calibrating, Peak-Detecting, Differential
Hall Effect Gear Tooth Sensor IC
ATS617LSG
Reference Target (Gear) Information
REFERENCE TARGET 60+2
SymCharacteristics
bol
Outside Diameter
Do
Typ.
Units
120
mm
Breadth of tooth, with respect
to branded face
6
mm
t
Length of tooth, with respect to
branded face; measured at Do
3
deg.
tSIG
Length of signature tooth, with
respect to branded face; measured at Do
15
deg.
Angular Valley
Thickness
tv
Length of valley, with respect to
branded face; measured at Do
3
deg.
Tooth Whole Depth
ht
3
mm
–
–
Face Width
Angular Tooth
Thickness
Signature Region
Angular Tooth
Thickness
Material
F
Test Conditions
Outside diameter of target
Low Carbon Steel
Symbol Key
t
Do
tSIG
ht
F
tv
Air Gap
Branded Face of Package
Signature Region
Pin 4
Pin 1
Branded Face
of Package
Reference Target
60+2
Figure 1. Configuration with Radial-Tooth Reference Target
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
5
Dynamic, Self-Calibrating, Peak-Detecting, Differential
Hall Effect Gear Tooth Sensor IC
ATS617LSG
Characteristic Data
Supply Current (On) versus Supply Voltage
Supply Current (On) versus Ambient Temperature
12
12
11
11
10
9
TA (°C)
–40
25
85
150
8
7
6
5
ICCON (mA)
ICCON (mA)
10
VCC (V)
8
4.5
12
18
24
7
6
5
4
4
3
0
5
10
15
VCC (V)
20
25
3
–50
30
50
100
150
200
Supply Current (Off) versus Ambient Temperature
12
11
11
10
10
9
TA (°C)
–40
25
85
150
8
7
6
5
ICCOFF (mA)
12
9
VCC (V)
8
4.5
12
18
24
7
6
5
4
4
3
0
TA (°C)
Supply Current (Off) versus Supply Voltage
ICCOFF (mA)
9
0
5
10
15
VCC (V)
20
25
30
3
–50
0
50
100
150
200
TA (°C)
Continued on the next page.
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
6
Dynamic, Self-Calibrating, Peak-Detecting, Differential
Hall Effect Gear Tooth Sensor IC
ATS617LSG
Output Voltage (On) versus Ambient Temperature
Output Voltage (On) versus Output Current
400
300
IOUT (mA)
5
10
15
20
200
100
0
–50
VSAT(ON) (mV)
VSAT(ON) (mV)
400
300
100
0
0
50
100
150
TA (°C)
–40
25
85
150
200
200
0
5
10
TA (°C)
Output Leakage Current (Off) versus Ambient Temperature
25
15
VOUT (V)
10
2.5
5
7.5
10
5
ICCOFF (μA)
IOUTOFF (μA)
20
Output Leakage Current (Off) versus Output Voltage
15
0
–50
15
IOUT (mA)
10
TA (°C)
–40
25
85
150
5
0
0
50
100
TA (°C)
150
200
0
2.5
5
7.5
10
12.5
VOUT (V)
Continued on the next page.
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
7
ATS617LSG
Dynamic, Self-Calibrating, Peak-Detecting, Differential
Hall Effect Gear Tooth Sensor IC
Edge Position versus Target Speed through Ambient Temperature Range
TA = –40°C
TA = 25°C
1.5
1.0
1.0
1.0
0.5
0
-0.5
-1.0
Edge Position (°)
1.5
Edge Position (°)
Edge Position (°)
1.5
-1.5
0.5
0
-0.5
-1.0
-1.5
0
0.5
1.0
1.5
Speed (krpm)
2.0
2.5
-1.0
0.5
1.0
1.5
Speed (krpm)
2.0
2.5
0
1.0
0
-0.5
-1.0
Edge Position (°)
1.0
Edge Position (°)
1.0
0.5
0.5
0
-0.5
-1.0
-1.5
1.0
1.5
Speed (krpm)
2.0
2.5
0.5
1.0
1.5
Speed (krpm)
2.0
2.5
0
1.0
Edge Position (°)
1.0
Edge Position (°)
1.0
0.5
0
-0.5
-1.0
-1.5
0
0.5
1.0
1.5
Speed (krpm)
2.0
2.5
0.5
1.0
1.5
Speed (krpm)
2.0
2.5
0
1.0
-1.5
Edge Position (°)
1.0
Edge Position (°)
1.0
-1.0
0.5
0
-0.5
-1.0
-1.5
1.0
1.5
Speed (krpm)
2.0
2.5
Air Gap (mm)
1.0
1.5
Speed (krpm)
2.0
2.5
Falling Edge
1.5
0.5
0.5
Falling Edge
-0.5
2.5
-1.0
1.5
0
2.0
0
-0.5
-1.5
0
Falling Edge
0.5
1.0
1.5
Speed (krpm)
0.5
1.5
0
0.5
Rising Edge
1.5
-1.5
2.5
-1.0
Rising Edge
-1.0
2.0
0
-0.5
1.5
-0.5
2.5
-1.5
0
Rising Edge
0
2.0
0.5
1.5
0.5
1.0
1.5
Speed (krpm)
Falling Edge
1.5
0.5
0.5
Falling Edge
1.5
0
Edge Position (°)
0
-0.5
1.5
-1.5
Edge Position (°)
0.5
-1.5
0
Falling Edge
Edge Position (°)
Sequential Region
Rising Edge
Rising Edge
Rising Edge
Signature Region
TA = 150°C
0.5
0
-0.5
-1.0
-1.5
0
0.5
0.5
1.0
1.5
Speed (krpm)
1.0
2.0
1.5
2.5
2.2
0
0.5
1.0
1.5
Speed (krpm)
2.5
Continued on the next page.
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
8
Dynamic, Self-Calibrating, Peak-Detecting, Differential
Hall Effect Gear Tooth Sensor IC
ATS617LSG
Edge Position versus Air Gap through Target Speed Range
Speed = 10 rpm
Speed = 500 rpm
1.5
1.0
1.0
1.0
0.5
0
-0.5
-1.0
Edge Position (°)
1.5
Edge Position (°)
Edge Position (°)
1.5
-1.5
0.5
0
-0.5
-1.0
-1.5
0
1.0
2.0
Air Gap (mm)
3.0
-1.0
1.0
2.0
Air Gap (mm)
3.0
0
1.0
0
-0.5
-1.0
Edge Position (°)
1.0
Edge Position (°)
1.0
0.5
0.5
0
-0.5
-1.0
-1.5
3.0
0.5
0
-0.5
-1.0
-1.5
0
1.0
2.0
Air Gap (mm)
3.0
0
1.0
1.0
-0.5
-1.0
-1.5
Edge Position (°)
1.0
Edge Position (°)
1.5
0
0.5
0
-0.5
-1.0
-1.5
1.0
2.0
Air Gap (mm)
3.0
0.5
0
-0.5
-1.0
-1.5
0
1.0
2.0
Air Gap (mm)
3.0
0
1.0
1.0
-0.5
-1.0
-1.5
Edge Position (°)
1.0
Edge Position (°)
1.5
0
0.5
0
-0.5
-1.0
-1.5
1.0
2.0
Air Gap (mm)
3.0
3.0
Falling Edge
1.5
0
1.0
2.0
Air Gap (mm)
Falling Edge
Falling Edge
1.5
0.5
3.0
Rising Edge
1.5
0
1.0
2.0
Air Gap (mm)
Rising Edge
Rising Edge
1.5
0.5
3.0
Falling Edge
1.5
1.0
2.0
Air Gap (mm)
1.0
2.0
Air Gap (mm)
Falling Edge
1.5
0
Edge Position (°)
0
-0.5
1.5
-1.5
Edge Position (°)
0.5
-1.5
0
Falling Edge
Edge Position (°)
Sequential Region
Rising Edge
Rising Edge
Rising Edge
Signature Region
Speed = 2000 rpm
0.5
0
-0.5
-1.0
-1.5
0
Ambient Temperature (°C)
1.0
2.0
Air Gap (mm)
-40
3.0
25
0
85
1.0
2.0
Air Gap (mm)
3.0
150
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
9
ATS617LSG
Dynamic, Self-Calibrating, Peak-Detecting, Differential
Hall Effect Gear Tooth Sensor IC
THERMAL CHARACTERISTICS may require derating at maximum conditions, see application information
Characteristic
Symbol
Test Conditions*
Single-sided PCB with copper limited to solder pads
RθJA
Package Thermal Resistance
in.2
Two-sided PCB with copper limited to solder pads and 3.57
(23.03 cm2) of copper area each side, connected to GND pin
Value
Units
126
ºC/W
84
ºC/W
Maximum Allowable VCC (V)
*Additional information is available on the Allegro website.
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)
(RQJA = 84 ºC/W)
(RQJA = 126 ºC/W)
VCC(min)
20
40
60
80
100
120
140
160
180
Power Dissipation, PD (m W)
Temperature (ºC)
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
(R
θJ
(R
θJ
20
40
60
A
=1
26
ºC
A
=
/W
84
ºC
/W
)
)
80
100
120
Temperature (°C)
140
160
180
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
10
ATS617LSG
Dynamic, Self-Calibrating, Peak-Detecting, Differential
Hall Effect Gear Tooth Sensor IC
Functional Description
Assembly Description The ATS617 gear-tooth sensor IC is a
Hall IC/rare-earth pellet configuration that is fully optimized to
provide detection of gear tooth edges. This device is packaged in
a molded miniature plastic body that has been optimized for size,
ease of assembly, and manufacturability. High operating temperature materials are used in all aspects of construction.
After proper power is applied to the component, the chip is
capable of instantly providing digital information that is representative of the profile of a rotating gear. No additional optimization or processing circuitry is required. This ease of use should
reduce design time and incremental assembly costs for most
applications.
Hall Technology The ATS617 contains a single-chip differential Hall effect sensor IC, a samarium cobalt pellet, and a
flat ferrous pole piece (figure 2). The Hall IC consists of 2 Hall
elements (spaced 2.2 mm apart) located so as to measure the
magnetic gradient created by the passing of a ferrous object. The
two elements measure the magnetic gradient and convert it to an
analog voltage that is then processed in order to provide a 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.
Internal Electronics The processing circuit uses a patented
peak detection scheme to eliminate magnet and system offsets.
This technique allows dynamic coupling and filtering of offsets
without the power-up and settling time disadvantages of classical
high-pass filtering schemes. The peak signal of every tooth and
valley is detected by the filter and is used to provide an instant
reference for the operate and release point comparator. In this
manner, the thresholds are adapted and referenced to individual
signal peaks and valleys, providing immunity to zero line variation from installation inaccuracies (tilt, rotation, and off-center
placement), as well as for variations caused by target and shaft
eccentricities.
The ATS617 also includes self-calibration circuitry that is
engaged at power on. The signal amplitude is measured, and
then the device gain is normalized. In this manner switchpoint
drift versus air gap is minimized, and excellent timing accuracy
can be achieved.
The AGC (Automatic Gain Control) circuitry, in conjunction
with a unique hysteresis circuit, also eliminates the effect of gear
edge overshoot as well as increases the immunity to false switching caused by gear tooth anomalies at close air gaps. The AGC
circuit sets the gain of the device after power-on.
V+
Differential
Input Signal
0
VPROC
Target (Gear)
Element Pitch
Hall Element 2
Dual-Element
Hall Effect Device
South Pole
North Pole
(Pin n >1 Side)
Hall Element 1
Hall IC
Pole Piece
(Concentrator)
Back-Biasing
Rare-Earth Pellet
Case
(Pin 1 Side)
Figure 2. Relative motion of the target is detected by the dual Hall elements mounted on the Hall IC.
BOP
BOP
BRP
BRP
V–
VCC
Device Output
VOUT
VOUT(sat)
Figure 3. The peaks in the resulting differential signal are used to set the
operate, BOP , and release, BRP , switchpoints.
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
11
ATS617LSG
Dynamic, Self-Calibrating, Peak-Detecting, Differential
Hall Effect Gear Tooth Sensor IC
Superior Performance The ATS617 peak-detecting differential design has several advantages over conventional Hall-effect
gear-tooth sensors. The signal-processing techniques used in the
ATS617 solve the catastrophic issues that affect the functionality
of conventional digital gear-tooth sensors, such as the following:
values change due to concentration effects, resulting in a varying
baseline with air gap, valley widths, eccentricities, and vibration
(figure 4). The differential configuration (figure 5) cancels the
effects of the back-biased field and avoids many of the issues
presented by the single Hall element design.
• Temperature drift. Changes in temperature do not greatly affect
this device due to the stable amplifier design and the offset
rejection circuitry.
• Timing accuracy variation due to air gap. The accuracy variation caused by air gap changes is minimized by the self-calibration circuitry. A 2×-to-3× improvement can be seen.
• Dual edge detection. Because this device switches based on the
positive and negative peaks of the signal, dual edge detection is
guaranteed.
• Tilted or off-center installation. Traditional differential sensors
can switch incorrectly due to baseline changes versus air gap
caused by tilted or off-center installation. The peak detector circuitry references the switchpoint from the peak and is immune
to this failure mode. There may be a timing accuracy shift
caused by this condition.
• Large operating air gaps. Large operating air gaps are achievable with this device due to the sensitive switchpoints after
power-on (dependent on target dimensions, material, and
speed).
• Immunity to magnetic overshoot. The patented adjustable
hysteresis circuit makes the ATS617 immune to switching on
magnetic overshoot within the specified air gap range.
Figure 4. Affect of varying valley widths on single-element circuits.
• Response to surface defects in the target. The gain-adjust
circuitry reduces the effect of minor gear anomalies that would
normally cause false switching.
• Immunity to vibration and backlash. The gain-adjust circuitry
keeps the hysteresis of the device roughly proportional to the
peak-to-peak signal. This allows the device to have good immunity to vibration even when operating at close air gaps.
• Immunity to gear run out. The differential chip configuration
eliminates the baseline variations caused by gear run out
Differential vs. Single-Element Design The differential
chip is superior in most applications to the classical single-element design. The single-element configuration commonly used
(Hall-effect element mounted on the face of a simple permanent
magnet) requires the detection of a small signal (often <100 G)
that is superimposed on a large back-biased field, often 1500 G to
3500 G. For most gear/target configurations, the back-biased field
Figure 5. Affect of varying air gaps on differential circuits.
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
12
Dynamic, Self-Calibrating, Peak-Detecting, Differential
Hall Effect Gear Tooth Sensor IC
ATS617LSG
Peak Detecting vs. AC-Coupled Filters High-pass filtering (normal AC coupling) is a commonly used technique for
eliminating circuit offsets. However, AC coupling has errors at
power-on because the filter circuit needs to hold the circuit zero
value even though the circuit may power-on over a large signal.
Such filtering techniques can only perform properly after the
filter has been allowed to settle, which typically takes longer than
1s. Also, high-pass filter solutions cannot easily track rapidly
changing baselines, such as those caused by eccentricities. (The
term baseline refers to a 0 G differential field, where each Halleffect element is subject to the same magnetic field strength; see
figure 3.) In contrast, peak detecting designs switch at the change
in slope of the differential signal, and so are baseline-independent
both at power-on and while running.
Peak Detecting vs. Zero-Crossing Reference The usual
differential zero-crossing sensor ICs are susceptible to false
switching due to off-center and tilted installations that result in a
shift of the baseline that changes with air gap. The track-and-hold
peak detection technique ignores baseline shifts versus air gaps
and provides increased immunity to false switching. In addition,
using track-and-hold peak detection techniques, increased air gap
capabilities can be expected because peak detection utilizes the
entire peak-to-peak signal range, as compared to zero-crossing
detectors, which switch at half the peak-to-peak signal.
Power-On Operation The device powers-on in the Off state
(output voltage high), irrespective of the magnetic field condition. The circuit is then ready to accurately detect the first target
edge that results in a high-to-low transition of the device output.
Undervoltage Lockout (UVLO) When the supply voltage,
VCC , is below the minimum operating voltage, VCC(UV) , the
device is off and stays off, irrespective of the state of the magnetic field. This prevents false signals, which may be caused
by undervoltage conditions (especially during power-up), from
appearing at the output.
Output. The device output is an open-drain stage. An external
pull-up (resistor) must be supplied to a supply voltage of not
more than VCC(max).
Output Polarity. The output of the unit will switch from low
to high as the leading edge of a tooth passes the branded face of
the package in the direction indicated in figure 6. This means that
in such a configuration, the output voltage will be high when the
package is facing a tooth. If the target rotation is in the opposite direction relative to the package, the output polarity will be
opposite as well, with the unit switching from low to high as the
leading edge passes the unit.
1
4
Figure 6. 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 branded face of the package. A right-to-left (pin 4 to pin 1) rotation
inverts the output signal polarity.
Target
Mechanical Profile
Target
Magnetic Profile
Branded Face
of Package
Rotating Target
Signature Tooth
B+
BIN
IC Output
Switch State
On
Off
On
Off
On
Off
On
Off
On
Off
On Off On Off On Off
V+
IC Output
Electrical Profile
Target Motion from
Pin 1 to Pin 4
VOUT
IC Output
Electrical Profile
Target Motion from
Pin 4 to Pin 1
VOUT
V+
Figure 7. 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
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
13
ATS617LSG
Dynamic, Self-Calibrating, Peak-Detecting, Differential
Hall Effect Gear Tooth Sensor IC
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 website.)
The Package Thermal Resistance, RJA, 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, RJC, is relatively
small component of RJA. 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 × RJA
(2)
TJ = TA + ΔT
(3)
For example, given common conditions such as: TA= 25°C,
VCC = 12 V, ICC = 6 mA, and RJA = 126 °C/W, then:
PD = VCC × ICC = 12 V × 6 mA = 72 mW

T = PD × RJA = 72 mW × 126 °C/W = 9°C
TJ = TA + T = 25°C + 9°C = 34°C
A worst-case estimate, PD(max), represents the maximum allowable power level (VCC(max), ICC(max)), without exceeding
TJ(max), at a selected RJA and TA.
Example: Reliability for VCC at TA = 150°C, package SG, using
minimum-K PCB.
Observe the worst-case ratings for the device, specifically:
RJA = 126 °C/W, TJ(max) = 165°C, VCC(max) = 24 V, and
ICC(max) = 12 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 ÷ RJA = 15°C ÷ 126 °C/W = 119 mW
Finally, invert equation 1 with respect to voltage:
VCC(est) = PD(max) ÷ ICC(max) = 119 mW ÷ 12 mA = 9.92 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 RJA. If VCC(est) ≥ VCC(max), then operation between
VCC(est) and VCC(max) is reliable under these conditions.
This value applies only to the voltage drop across the ATS617
chip. If a protective series diode or resistor is used, the effective maximum supply voltage is increased. For example, when a
standard diode with a 0.7 V drop is used:
VCC(max) = 9.9 V + 0.7 V = 10.6 V
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
14
Dynamic, Self-Calibrating, Peak-Detecting, Differential
Hall Effect Gear Tooth Sensor IC
ATS617LSG
Package SG 4-Pin SIP
5.50±0.05
F
2.20
E
B
8.00±0.05
LLLLLLL
NNN
5.80±0.05
E1
E2
YYWW
Branded
Face
1.70±0.10
D
4.70±0.10
1
2
3
4
= 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
A
0.60±0.10
Standard Branding Reference View
0.71±0.05
For Reference Only, not for tooling use (reference DWG-9002)
Dimensions in millimeters
A Dambar removal protrusion (16X)
+0.06
0.38 –0.04
B Metallic protrusion, electrically connected to pin 4 and substrate (both sides)
C Thermoplastic Molded Lead Bar for alignment during shipment
24.65±0.10
D Branding scale and appearance at supplier discretion
0.40±0.10
15.30±0.10
E
Active Area Depth, 0.43 mm
F
Hall elements (E1, E2), not to scale
1.0 REF
A
1.60±0.10
C
1.27±0.10
0.71±0.10
0.71±0.10
5.50±0.10
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
15
ATS617LSG
Dynamic, Self-Calibrating, Peak-Detecting, Differential
Hall Effect Gear Tooth Sensor IC
Copyright ©2009, Allegro MicroSystems, Inc.
The products described herein are manufactured under one or more of the following U.S. patents: 5,264,783; 5,389,889; 5,442,283; 5,517,112;
5,581,179; 5,619,137; 5,621,319; 5,650,719; 5,686,894; 5,694,038; 5,729,130; 5,917,320; 6,091,239; 6,100,680; 6,232,768; 6,242,908; 6,265,865;
6,297,627; 6,525,531; 6,690,155; 6,693,419; 6,919,720; 7,046,000; 7,053,674; 7,138,793; 7,199,579; 7,253,614; 7,365,530; 7,368,904; or 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’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 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.
For the latest version of this document, visit our website:
www.allegromicro.com
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
16