ATS685 Datasheet

ATS685LSH
Two-Wire, Zero Speed
Differential Gear Tooth Sensor IC
Description
Features and Benefits
• Fully optimized differential digital gear tooth sensor IC
• Running Mode Lockout
• Unique algorithms for increased vibration immunity
• AGC and reference adjust circuit
• Air gap independent switchpoints
• Digital output representing gear profile
• Precise duty cycle throughout operating temperature range
• Large operating air gap range
• Short power-on time
• True zero-speed operation
• Undervoltage lockout (UVLO)
• Wide operating voltage range
• Internal current regulator for two-wire operation
• Single-chip sensing IC for high reliability
• Robust test coverage capability using Scan Path
and IDDQ measurement
Package: 4-pin SIP (suffix SH)
The ATS685LSH is an optimized Hall-effect sensing integrated
circuit and rare-earth pellet combination that provides a
user-friendly solution for true zero-speed digital gear-tooth
sensing in two-wire applications. The sensor IC consists of a
single-shot molded plastic package that includes a samarium
cobalt pellet, a pole piece, and a Hall Effect 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 single integrated circuit incorporates a dual element
Hall-effect sensor IC and signal processing circuitry that
switches in response to differential magnetic signals created
by ferromagnetic targets. The device contains a sophisticated
compensating circuit to eliminate magnetic and system offsets.
Digital tracking of the analog signal is used to achieve true
zero speed operation. Advanced calibration algorithms are
used to adjust the device gain and offset at power-up, resulting
in air gap independent switchpoints, which greatly improves
output accuracy. In addition, advanced algorithms mitigate the
effect of system anomalies such as target vibration and sudden
changes in air gap.
The regulated current output is configured for two-wire
operation. This sensor IC is ideal for obtaining edge and duty
cycle information in gear-tooth–based applications such as
transmission speed.
Not to scale
The ATS685 is provided in a 4-pin SIP package that is lead
(Pb) free, with 100% matte tin leadframe plating.
Functional Block Diagram
VCC
Voltage
Regulator
PDAC
Hall
Amp
Offset
Adjust
AGC
NDAC
Reference
Generator
and
Lockout
Synchronous Digital Controller
TEST
Multiplexor
GND
ATS685LSH-DS
Two-Wire, Zero Speed
Differential Gear Tooth Sensor IC
ATS685LSH
Selection Guide
Part Number
Packing*
ATS685LSHTN-T
13-in. reel, 800 pieces per reel
*Contact Allegro™ for additional packing options
Absolute Maximum Ratings
Characteristic
Symbol
Supply Voltage
VCC
Reverse Supply Voltage
VRCC
Rating
Units
26.5
V
–18
V
–40 to 150
ºC
TJ(max)
165
ºC
Tstg
–65 to 170
ºC
Operating Ambient Temperature
TA
Maximum Junction Temperature
Storage Temperature
Pin-out Diagram
Notes
Range L, refer to Power Derating Curve
Terminal List Table
Number
Name
1
VCC
Function
2
NC
3
TEST
Test (float or tie to GND)
4
GND
Ground
Supply voltage
No connection (float or tie to GND)
1 2 3 4
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
2
Two-Wire, Zero Speed
Differential Gear Tooth Sensor IC
ATS685LSH
OPERATING CHARACTERISTICS VCC and TA within specification, unless otherwise noted
Characteristics
Symbol
Test Conditions
Min.
VCC
Operating, TJ < TJ (max), ICC within specification
Typ.1
Max.
Unit2
V
Electrical Characteristics
Supply Voltage3
Undervoltage Lockout
Reverse Supply Current4
VCC(UV)
IRCC
4.0
–
24
VCC 0 → 5 V or 5 → 0 V
–
3.5
3.95
V
VCC = –18 V
–
–
–10
mA
Supply Zener Clamp Voltage
VZ
ICC = ICC (max) + 3 mA, TA = 25°C
28
–
–
V
Supply Zener Current
IZ
TA = 25°C, VCC = 28 V
–
–
19
mA
Supply Current
Supply Current Ratio
Test Pin Zener Clamp Voltage5
ICC(Low)
Low-current state
4
6
8
mA
ICC(High)
High-current state
12
14
16
mA
ICC(High)
/ ICC(Low)
Ratio of high current to low current
1.85
–
3.05
–
–
6
–
V
VZTEST
Power-On State Characteristics
Power-On Time6
tPO
VCC > VCC (min), fOP < 100 Hz
–
1
2
ms
Power-On State7
POS
t > tPO
–
ICC(High)
–
A
di / dt
Δi / Δt from 90% to 10% ICC level
RSENSE = 100 Ω, CLOAD = 10 pF, no CBYPASS
7
14
–
mA/μs
0
–
12
kHz
Output Stage
Output Slew Rate8,9
Performance Characteristics
Operating Frequency
fOP
Analog Signal Bandwidth
BW
16
20
–
kHz
–
70
–
%
Operate Point
BOP
% of peak-to-peak BSIG , AGOP within
specification
Release Point
BRP
% of peak-to-peak BSIG , AGOP within
specification
–
30
–
%
Running Mode Lockout Enable
Threshold
VLOE(RM)
At peak-to-peak VPROC < VLOE(RM) , output
switching disables
–
170
–
mV
Running Mode Lockout Release
Threshold
VLOR(RM)
At peak-to-peak VPROC > VLOR(RM) , output
switching enables
–
200
–
mV
–
VLOR(RM)
–
mV
Rising output (current) edges, fOP < 200 Hz
–
–
3
edges
Calibration
Start Mode Hysteresis
Initial Calibration10
POHYS
CALI
Continued on the next page…
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
3
Two-Wire, Zero Speed
Differential Gear Tooth Sensor IC
ATS685LSH
OPERATING CHARACTERISTICS (continued) VCC and TA within specification, unless otherwise noted
Min.
Typ.1
Max.
Unit2
Differential magnetic signal, duty cycle within
specification
50
–
1500
GPK-PK
BSIGEXT
Differential magnetic signal, output switching (no
missed edges), duty cycle not guaranteed
30
–
–
GPK-PK
Operational Air Gap Range
AGOP
Using Allegro Reference Target 60-0, duty cycle
within specification
0.5
–
2.5
mm
Extended Operational Air Gap Range
AGEXT
Using Allegro Reference Target 60-0, output
switching (no missed edges), duty cycle not
guaranteed
–
–
3.0
mm
±60
–
–
G
Wobble < 0.5 mm, AG within specification
–
–
±10
%
Instantaneous symmetric magnetic signal
amplitude change, measured as a percentage of
peak-to-peak BSIG, fOP < 500 Hz
–
45
–
%
Characteristics
Symbol
Test Conditions
Functional Characteristics
Operating Signal Range11
Extended Operating Signal Range
Allowable User-Induced Differential
Offset
Duty Cycle Variation12
Maximum Sudden Signal Amplitude
Change
BSIG
BDIFFEXT
ΔD
BSIG(INST)
Operation within specification
1Typical
values are at TA = 25°C and VCC = 12 V. Performance may vary for individual units, within the specified maximum and minimum limits.
G (gauss) = 0.1 mT (millitesla).
3Maximum voltage must be adjusted for power dissipation and junction temperature; see Power Derating section.
4Negative current is defined as conventional current coming out of (sourced from) the specified device terminal.
5Sustained voltages beyond the clamp voltage may cause permanent damage to the IC.
6Measured from V
CC ≥ VCC (min) to the time when the device is able to switch the output signal in response to a magnetic stimulus.
7Please refer to the Functional Description, Power-On section.
8di is the difference between 10% of I
CC(Low) and 90% of ICC(High) . dt is the time period between those two points.
9C
LOAD is the probe capacitance of the oscilloscope used to make the measurement.
10For power-on frequency, f
OP < 200 Hz. Higher power-on frequencies may result in more input magnetic cycles until full output edge accuracy is
achieved, including the possibility of missed output edges.
11AG
OP 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 table.
12Target rotation from pin 4 to pin 1.
21
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
4
Two-Wire, Zero Speed
Differential Gear Tooth Sensor IC
ATS685LSH
Reference Target 60-0 (60 Tooth Target)
Characteristics
Symbol
Test Conditions
Typ.
Units
120
mm
Outside diameter of target
Face Width
F
Breadth of tooth, with respect
to branded face
6
mm
Angular Tooth Thickness
t
Length of tooth, with respect
to branded face
3
deg.
Angular Valley Thickness
tv
Length of valley, with respect
to branded face
3
deg.
Tooth Whole Depth
ht
3
mm
–
–
Material
Branded Face
of Package
ØDO
ht
F
t
tV
Do
Outside Diameter
Symbol Key
Low Carbon Steel
Air Gap
Reference Gear Magnetic Gradient Amplitude versus Air Gap
Reference Target 60-0, Hall element spacing 2.20 mm
1000
800
600
400
Branded Face
of Package
200
0
0
1
2
3
Reference Target
60-0
Air Gap (mm)
Reference Gear Magnetic Profile
Reference Target 60-0, Hall element spacing 2.20 mm
600
Air Gap (mm)
400
0.50
0.75
Differential B (G)
Peak-to-Peak Differential B (G)
1200
1.00
200
1.25
1.50
0
1.75
2.00
2.25
200
2.50
2.75
3.00
400
3.00 mm AG
0.50 mm AG
600
0
2
4
6
8
10
12
14
16
18
20
Gear Rotation (°)
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
5
Two-Wire, Zero Speed
Differential Gear Tooth Sensor IC
ATS685LSH
Thermal Characteristics may require derating at maximum conditions, see Power Derating section
Characteristic
Symbol
Test Conditions*
Single layer PCB, with copper limited to solder pads
RθJA
Package Thermal Resistance
Single layer PCB, with copper limited to solder pads and 3.57
cm2) copper area each side
in.2
(23.03
Value
Unit
126
ºC/W
84
ºC/W
*Additional thermal information available on the Allegro website
Maximum Allowable VCC (V)
Power Derating Curve
At maximum supply current, ICC = ICC(High)(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)
(R θJA = 84 °C/W)
(R θJA = 126 °C/W)
VCC(min)
20
40
60
80
100
120
140
160
180
Temperature (°C)
Power Dissipation versus Ambient Temperature
2600
At maximum supply current, ICC = ICC(High)(max)
2400
Power Dissipation, PD (m W)
2200
2000
1800
1600
1400
RQJA = 84 ºC/W
1200
1000
800
RQJA = 126 ºC/W
600
400
200
0
20
40
60
80
100
120
140
Temperature,TA (°C)
160
180
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
6
Two-Wire, Zero Speed
Differential Gear Tooth Sensor IC
ATS685LSH
Functional Description
Sensing Technology
The ATS685 sensor IC contains a single-chip differential Halleffect circuit, a samarium cobalt pellet, and a flat ferrous pole
piece (a precisely-mounted magnetic field concentrator that
homogenizes the flux passing through the Hall chip). As shown in
figure 1, the circuit supports two Hall elements, which sense the
Target (Gear)
Element Pitch
Hall Element 2
South Pole
Dual-Element
Hall Effect Device
Hall Element 1
Hall IC
Pole Piece
(Concentrator)
Back-biasing
Rare-earth Pellet
Case
North Pole
(Pin 4 Side)
(Pin 1 Side)
Figure 1. Relative motion of the target is detected by the dual Hall
elements mounted on the Hall IC.
Mechanical Position (Target moves past sensor pin 1 to pin 4)
Target
(Gear)
This tooth
sensed earlier
This tooth
sensed later
Target Magnetic Profile
+B
Device Package Orientation to Target
Element Pitch
Device Branded Face
Hall Element 2
Hall Element 1
IC
(Pin 4 Side)
(Pin 1 Side)
(View of Side
Away from Pins)
Device Internal Differential Analog Signal, VPROC
BOP(#1)
Device Internal Switch State
Off
On
+t
Off
The Hall IC is self-calibrating and also integrates 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
Under normal operating conditions, the IC is capable of providing digital information that is representative of the mechanical
features of a rotating gear. The waveform diagram in figure 2
presents the automatic translation of the mechanical profile,
through the magnetic profile that it induces, to the digital output
signal of the ATS685. No additional optimization is needed
and minimal processing circuitry is required. This ease of use
reduces design time and incremental assembly costs for most
applications.
Diagnostics
The regulated current output is configured for two-wire applications, requiring one less wire for operation than do switches with
the 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 3 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.
+mA
BOP(#2)
BRP(#1)
magnetic profile of the ferromagnetic 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.
ICC(HIGH)(max)
ICC(HIGH)(min)
On
ICC(LOW)(max)
Device Output Signal, ICC
ICC(LOW)(min)
+t
Figure 2. The magnetic profile reflects the geometry of the target, allowing
the ATS685 to present an accurate digital output response.
Short

Range for Valid ICC(HIGH)

Range for Valid ICC(LOW)
Fault
Open
0
Figure 3. Diagnostic characteristics of supply current values.
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115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
7
Two-Wire, Zero Speed
Differential Gear Tooth Sensor IC
ATS685LSH
Determining Output Signal Polarity
In figure 2, the top panel, labeled Mechanical Position, represents
the mechanical features of the target gear and orientation to the
device. The bottom panel, labeled Device Output Signal, displays
the square waveform corresponding to the digital output signal
(current amplitude) that results from a rotating gear configured
as shown in figure 3. Referring to the target side nearest the face
of the sensor IC, the direction of rotation is: perpendicular to the
leads, across the face of the device, from the pin 1 side to the
pin 4 side.
Output Polarity States
RSENSE Location
ICC State
VSENSE State
High side
(VCC pin side)
High
Low
Low
High
Low side
(GND pin side)
High
High
Low
Low
VCC
VCC
In order to read the output signal as a voltage, VSENSE , a sense
resistor, RSENSE , can be placed on either the VCC signal or on
the GND signal. As shown in figure 4, when RSENSE is placed on
the GND signal, the output signal voltage, VSENSE(LowSide) , is in
phase with ICC . When RSENSE is placed on the VCC signal, the
output signal voltage, VSENSE(HighSide) , is inverted relative to ICC .
ICC
RSENSE
ICC
VSENSE(HighSide)
1
1
VCC
VCC
ATS685
ATS685
GND
4
VSENSE(LowSide)
GND
4
RSENSE
Branded Face
of Package
Rotating Target
I+
ICC
V+
VSENSE(LowSide)
V+
VSENSE(HighSide)
Pin 1
Pin 4
Figure 3. This figure depicts left-to-right (pin 1 to pin 4) direction of target
rotation.
Figure 4. Alternative Polarity Configurations Using Two-Wire Sensing.
The Output Polarity States table provides the permutations of output
voltage relative to ICC, given alternative locations for RSENSE. Panel A
shows the low-side, VSENSE(LowSide) , sensing configuration, and panel B
shows the high-side, VSENSE(HighSide) , configuration. As shown in panel
C, VSENSE(LowSide) is in phase with ICC , and VSENSE(HighSide) , is inverted.
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
8
Two-Wire, Zero Speed
Differential Gear Tooth Sensor IC
ATS685LSH
Continuous Update of Switchpoints
Switchpoints are the threshold levels of the differential internal
analog signal, VPROC , at which the device changes output signal
state. The value of VPROC is directly proportional to the magnetic flux
density, B, induced by the target and sensed by the Hall elements.
As VPROC rises through a certain limit, referred to as the operate
point, BOP , the output state changes from high to low. As VPROC
falls below BOP to a certain limit, the release point, BRP , the output
state changes from low to high.
(A) TEAG varying; cases such as
eccentric mount, out-of-round region,
normal operation position shift
As shown in figure 5, threshold levels for the switchpoints are
established as a function of the peak input signal levels. The device
incorporates an algorithm that continuously monitors the input signal
and updates the switching thresholds accordingly with limited inward
movement of VPROC. The switchpoint for each edge is determined
by the detection of the previous two signal edges. In this manner,
variations are tracked in real time.
(B) Internal analog signal, VPROC,
typically resulting in the IC
V+
Smaller
TEAG
IC
Target
Smaller
TEAG
Larger
TEAG
VPROC (V)
Target
Hysteresis Band
(Delimited by switchpoints)
Larger
TEAG
IC
Smaller
TEAG
0
Target Rotation (°)
360
(C) Internal analog signal, VPROC, representing
magnetic field for digital output
V+
BOP
VPROC (V)
BOP
BRP
BOP
BRP
BOP
BOP
BRP
BRP
VOUT (V)
BRP
BOP
Figure 5. The Continuous Update algorithm allows the Allegro IC to interpret and adapt to variances in the magnetic field generated by the target
as a result of eccentric mounting of the target, out-of-round target shape, and similar dynamic application problems that affect the TEAG (Total
Effective Air Gap). As shown in panel A, the variance in the target position results in a change in the TEAG. This affects the IC 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 switchpoints based on the fluctuation of VPROC, as shown in panel C.
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115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
9
Two-Wire, Zero Speed
Differential Gear Tooth Sensor IC
ATS685LSH
Power-On
The ATS685 is guaranteed to power-on in the high current state,
ICC(High) . When power (VCC > VCC (min) ) is applied to the
device, a short period of time is required to power the various portions of the circuit. During this period, the ATS685 will
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, CALI . However, this period allows the device to optimize
for running mode operation. As shown in figure 6, the first three
high peak signals corresponding to rising output edges are used to
calibrate AGC (Automatic Gain Control). There is a slight variance in the duration of initialization, depending on what target
feature is opposite the sensor IC when power-on occurs. Also, a
high speed of target rotation at power-on may increase the quantity required in the CALI period.
Target
(Gear)
4
VPR
OC
Power-on 1
opposite
tooth
Start Mode
Hysteresis
Overcome
AGC Calibration
OC
3
2
1
VPR
Device
Position
Running Mode
ICC
Start Mode
Hysteresis
Overcome
AGC Calibration
VPR
VPR
OC
Power-on
at falling
2
mechanical
edge
OC
ICC
Running Mode
ICC
Start Mode
Hysteresis
Overcome
AGC Calibration
OC
VPR
VPR
Power-on
opposite 3
valley
OC
ICC
Running Mode
ICC
Start Mode
Hysteresis
Overcome
ICC
AGC Calibration
OC
VPR
VPR
Power-on
4
at rising
mechanical
edge
OC
ICC
Running Mode
ICC
Figure 6. 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 IC in the direction indicated (from pin 1 to pin 4) and the voltage output is configured for low-side sensing, VOUT(Low). 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 when fOP ≤ 200 Hz, and more may be required at greater speeds.
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115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
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ATS685LSH
Two-Wire, Zero Speed
Differential Gear Tooth Sensor IC
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 device on such
spurious signals. Calibration can be performed using the actual
target features.
A typical scenario is shown in figure 7. 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
ATS685 starts to compute switchpoints.
Target, Gear
Target Magnetic Profile
IC Position
Relative to Target
Differential Signal, VPROC
2
1
3
4
BOP(initial)
BRP
Start Mode
Hysteresis, POHYS
BOP
BRP
BRP(initial)
Output Signal, ICC
If exceed POHYS
on high side
If exceed POHYS
on low side
Figure 7. Operation of Start Mode Hysteresis
• At power-on (position 1), the ATS685 begins sampling VPROC .
• At the point where the Start Mode Hysteresis, POHYS, is exceeded, the device establishes an initial switching threshold, by
using the Continuous Update algorithm. If VPROC is rising through the limit on the high side (position 2), the switchpoint is
BOP , and if VPROC is falling through the limit on the low side (position 4), it is BRP . 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.
• In either case (BOP or BRP), because the switchpoint is immediately passed as soon as it is established, the ATS685 enables switching:
▫ If on the high side, at BOP (position 2) the output would switch from low to high. However, because output is already high,
no output switching occurs.
At the next switchpoint, where BRP is passed (position 3), the output switches from high to low.
▫ If on the low side, at BRP (position 4) the output switches from high to low.
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
11
Two-Wire, Zero Speed
Differential Gear Tooth Sensor IC
ATS685LSH
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 device. Because VCC is
below the VCC(min) specification during lockout, the ICC levels
may not be within specification.
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 for information on the circuitry
needed for compliance with various EMC specifications. Refer to
figure 8 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 is then automatically adjusted. Figure 9 illustrates the effect of this feature.
Running Mode Gain Adjust
The ATS685 has a feature during Running mode to compensate
for dynamic air gap variation. If the system increases the mag-
V CC
netic input drastically, the device will gradually readjust the gain
downwards, allowing the chip to regain the optimum internal
electrical signal with the new, larger, magnetic signal.
Dynamic Offset Cancellation (DOC)
The offset circuitry when combined with AGC automatically
reduces the effects of chip, magnet, and installation offsets. This
circuitry is continuously active, including both Power-on mode
and Running mode, compensating for any offset drift (within
Allowable User-Induced Differential Offset). Continuous operation also allows it to compensate for offsets induced by temperature variations over time.
Running Mode Lockout
The ATS685 has a Running mode lockout feature to prevent
switching on small signals that are characteristic of vibration
signals. The internal logic of the chip evaluates small signal
amplitudes below a certain level to be vibration. In that event, the
output is blanked (locked-out) until the amplitude of the signal
returns to normal operating levels.
Watchdog
The ATS685 employs a watchdog circuit to prevent extended loss
of output switching during sudden impulses and vibration in the
system. If the system changes the magnetic input drastically such
that target feature detection is terminated, the device will fully
reset itself, allowing the chip to recalibrate properly on the new
magnetic input signal.
Ferrous Target
Mechanical Profile
1
2
ATS685
V+
3
0.01 MF (optional)
CBYPASS
Internal Differential
Analog Signal
Response, without AGC
AGLarge
AGSmall
4
V+
RSENSE
100 7
CLOAD
Figure 8. Typical circuit for proper device operation.
Internal Differential
Analog Signal
Response, with AGC
AGSmall
AGLarge
Figure 9. 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, as shown in the lowest panel.
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
12
Two-Wire, Zero Speed
Differential Gear Tooth Sensor IC
ATS685LSH
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 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)
Example: Reliability for VCC at TA = 150°C, package SH, using a
single-layer PCB.
Observe the worst-case ratings for the device, specifically:
RJA = 126 °C/W, TJ(max) = 165°C, VCC(max) = 28 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 ÷ 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 ÷ 16 mA = 7.4 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.
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 = 9.1°C
TJ = TA + T = 25°C + 9.1°C = 34.1°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.
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
13
Two-Wire, Zero Speed
Differential Gear Tooth Sensor IC
ATS685LSH
Package SH, 4-Pin SIP
F
5.50±0.05
1.10
E
1.10 F
B
8.00±0.05
LLLLLLL
NNN
5.80±0.05
E1
E2
YYWW
Branded
Face
1.70±0.10
5.00±0.10
D
4.00±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-9003)
Dimensions in millimeters
A Dambar removal protrusion (16X)
24.65±0.10
B Metallic protrusion, electrically connected to pin 4 and substrate (both sides)
C Thermoplastic Molded Lead Bar for alignment during shipment
+0.06
0.38 –0.04
1.00±0.10
13.10±0.10
D Branding scale and appearance at supplier discretion
E Active Area Depth 0.43 mm REF
F
Hall elements (E1, E2); not to scale
A
1.0 REF
1.60±0.10
C
1.27±0.10
0.71±0.10
0.71±0.10
5.50±0.10
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
14
ATS685LSH
Two-Wire, Zero Speed
Differential Gear Tooth Sensor IC
Copyright ©2011-2013, Allegro MicroSystems, LLC
Allegro MicroSystems, LLC 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, LLC 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, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
15
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