Allegro ATS675LSETN-HT-T Self-calibrating tpos speed sensor optimized for automotive cam sensing application Datasheet

ATS675LSE
Self-Calibrating TPOS Speed Sensor
Optimized for Automotive Cam Sensing Applications
Features and Benefits
Description
▪ Chopper stabilized; optimized for automotive cam
sensing applications
▪ Optimized absolute timing accuracy step size through
gradual transition from TPOS to Running Mode
▪ High immunity to signal anomalies resulting from
magnetic overshoot and peak-to-peak field variation
▪ Tight timing accuracy over full operating
temperature range
▪ True zero-speed operation
▪ Automatic Gain Control circuitry for air gap
independent switchpoints
▪ Operation at supply voltages down to 3.3 V
▪ Digital output representing target profile
▪ Undervoltage lockout (UVLO)
▪ Patented Hall IC-magnet system
▪ Increased output fall time for improved radiated
emissions performance
The ATS675 is the next generation of the Allegro® True
Power-On State (TPOS) sensor family, offering improved
accuracy compared to prior generations, gradual TPOS to
Running Mode adjustment for accuracy-shift reduction,
and longer output fall time for improved radiated emissions
performance. The ATS675 provides absolute zero-speed
performance and TPOS information.
The sensor incorporates a single-element Hall IC with an
optimized custom magnetic circuit that switches in response
to magnetic signals created by a ferromagnetic target. The IC
contains a sophisticated digital circuit designed to eliminate
the detrimental effects of magnet and system offsets. Signal
processing is used to provide device performance at zero target
speed, independent of air gap, and which adapts dynamically
to the typical operating conditions found in automotive
applications, particularly camshaft-sensing applications.
High resolution peak-detecting DACs are used to set the adaptive
switching thresholds of the device, ensuring high accuracy
despite target eccentricity. Internal hysteresis in the thresholds
reduces the negative effects of anomalies in the magnetic signal
(such as magnetic overshoot) associated with targets used in
many automotive applications. The resulting output of the
device is a digital representation of the ferromagnetic target
profile. The ATS675 also includes a low bandwidth filter that
increases the noise immunity and the signal-to-noise ratio of
the sensor.
Package: 4-pin SIP module (suffix SE)
1
Not to scale
2
3
The device package is lead (Pb) free, with 100% matte tin
leadframe plating.
4
Typical Application
VS
VPU
CBYPASS
0.1 μF
RPU
1
VCC
3
A
ATS675
TEST
OUT
GND
4
Sensor
Output
2
CL
A Recommended
Figure 1. Operational circuit for the ATS675
ATS675LSE-DS
Self-Calibrating TPOS Speed Sensor
Optimized for Automotive Cam Sensing Applications
ATS675LSE
Selection Guide
Part Number
Output Protocol
Packing*
ATS675LSETN-LT-T
Output low opposite target tooth
ATS675LSETN-HT-T
Output high opposite target tooth
*Contact Allegro for additional packing options
13-in. reel, 450 pieces per reel
Absolute Maximum Ratings
Characteristic
Symbol
Notes
Rating
Units
Supply Voltage
VCC
28
V
Reverse Supply Voltage
VRCC
–18
V
Reverse Supply Current
IRCC
–50
mA
20
mA
–40 to 150
ºC
Output Current
IOUT(sink)
Internal current limiting is intended to protect
the device from output short circuits, but is not
intended for continuous operation.
Operating Ambient Temperature
TA
Maximum Junction Temperature
TJ(max)
165
ºC
Tstg
–65 to 170
ºC
Storage Temperature
Range L
Thermal Characteristics may require derating at maximum conditions, see application information
Characteristic
Symbol
RθJA
Package Thermal Resistance
Test Conditions*
Value
Units
1-layer PCB with copper limited to solder pads
101
ºC/W
2-layer PCB with copper limited to solder pads
and 3.57 in.2 of copper area each side
77
ºC/W
*Additional thermal information available on the Allegro website
Power Dissipation versus Ambient Temperature
Power Derating Curve
30
VCC(max)
20
(RQJA = 77 ºC/W)
15
(RQJA = 101 ºC/W)
10
5
0
20
VCC(min)
40
60
80
100
120
Temperature, TA (ºC)
140
160
180
Power Dissipation, PD (mW)
Maximum Allowable VCC (V)
25
1900
1800
1700
1600
1500
1400
1300
1200
1100
1000
900
800
700
600
500
400
300
200
100
0
(R
QJ
A
=
77
(R
QJ
20
40
60
A
=1
01
ºC
/W
ºC
/W
)
)
80
100
120
140
Temperature, TA (°C)
160
180
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
2
Self-Calibrating TPOS Speed Sensor
Optimized for Automotive Cam Sensing Applications
ATS675LSE
Functional Block Diagram
VCC
Multiplexed Test
Signals
NDAC
Internal Regulator
(Analog)
Internal Regulator
(Digital)
Update
Logic
Baseline
Trim
Oscillator
Hall
Amp
TEST
+/ –
Low Pass
Filter
Running Mode
Threshold
Selector
OUT
PDAC
Mode
Control
DDA
+/ –
Auto Gain
Adjust
Temperature
Compensation
Trim
Dynamic
Threshold
DAC
TPOS
Trim
Current
Limit
GND
TPOS
Pin-out Diagram
Terminal List
1 2
3
Number
Name
Function
1
VCC
Supply voltage
2
OUT
Open drain output
3
TEST
Test pin; connection to GND recommended
4
GND
Ground
4
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
3
ATS675LSE
Self-Calibrating TPOS Speed Sensor
Optimized for Automotive Cam Sensing Applications
OPERATING CHARACTERISTICS Valid using reference target 8X, TA ,TJ , and VCC within specification, unless otherwise noted
Characteristics
Symbol
Test Conditions
Min.
Typ.1
Max.
Unit
Electrical Characteristics
Supply Voltage2
VCC
Operating, TJ < TJ(max)
3.3
–
24
V
Undervoltage Lockout
VCCUV
VCC = 0 → 5 V or 5 → 0 V
–
–
3.3
V
Supply Zener Clamp Voltage
VZsupply
ICC = ICC(max) + 3 mA, TA = 25°C
28
33
40
V
Supply Zener Current3
IZsupply
VS = 28 V
–
–
13
mA
–
6.5
10
mA
–
–5
–10
mA
–
500
–
kHz
VCC > VCC(min), fSIG < 200 Hz
–
–
1
ms
IOUT = 10 mA, output in on-state
–
–
400
mV
Supply Current
ICC
Reverse Battery Current4
IRCC
Chopping Frequency
VRCC = –18 V
fc
Power-On Characteristics
Power-On Time5
tPO
Output Stage Characteristics
Output On Voltage
VOUT(SAT)
IOUT = 15 mA, output in on-state
–
–
450
mV
VZOUT
IOUT = 3 mA, TA = 25°C
30
–
–
V
Output Current Limit
IOUTLIM
Output in on-state
30
50
80
mA
Output Leakage Current
IOUTOFF
VOUT = 24 V, output in off-state
–
0.1
10
μA
Output Zener Voltage
Time6
td
4 kHz sinusoidal signal, falling electrical edge
–
22
–
μs
Output Rise Time
tr
RPU = 1 kΩ, CL = 4.7 nF, VPU = 5 V
–
10.3
–
μs
Output Fall Time7
tf
TA = 25°C, RPU = 1 kΩ,
CL = 4.7 nF
Output Delay
Output Fall Time Variation Over
Temperature Range
Output Polarity
Δtf
VOUT
VPU = 5 V
5
8
15
μs
VPU = 12 V
–
15
–
μs
–
±0.2
–
%/°C
Maximum variation from TA = 25°C
HT device package
option
Opposite target tooth
–
High
–
V
Opposite target valley
–
Low
–
V
LT device package
option
Opposite target tooth
–
Low
–
V
Opposite target valley
–
High
–
V
TPOS functionality guaranteed
0.5
–
3.0
mm
Output switching in Running Mode, TPOS
function not guaranteed
3.0
–
4.5
mm
Performance Characteristics
Operational Air Gap Range8
Extended Air Gap Range9
AGTPOS
AGEXTMAX
ErrRELR
Rising mechanical edges after initial calibration,
gear speed = 1000 rpm, target eccentricity
< 0.1 mm
–
0.4
0.8
deg.
ErrRELF
Falling mechanical edges after initial calibration,
gear speed = 1000 rpm, target eccentricity
< 0.1 mm
–
0.5
1.0
deg.
Relative Timing Accuracy10,11
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
4
ATS675LSE
Self-Calibrating TPOS Speed Sensor
Optimized for Automotive Cam Sensing Applications
OPERATING CHARACTERISTICS (continued) Valid using reference target 8X, TA , TJ , and VCC within specification, unless otherwise noted
Characteristics
Symbol
Test Conditions
Min.
Typ.1
Max.
Unit
Tooth Speed
fSIG
Tooth signal frequency, sinusoidal input signal
0
–
8000
Hz
Analog Signal Bandwidth
BW
Equivalent to –3 dB cutoff frequency
–
20
–
kHz
Switchpoint
BST
% of peak-to-peak, referenced to tooth signal
(see figure 4)
–
30
–
%
Internal Hysteresis12
BHYS
% of peak-to-peak signal
–
10
–
%
CALI
Quantity of mechanical falling edges during
which device is in full TPOS Mode
–
–
4
Edges
1
–
16
Teeth
Switchpoint Characteristics
Calibration
Initial Calibration13
TPO to Running Mode Adjustment
Quantity of target teeth after CALI over which
CALTPORM TPOS to Running Mode threshold adjustment
occurs
Signal Characteristics
Breduce(G)
Reduction in VPROC amplitude from VPROC(high)
to lowest peak VPROC(reduce), all specifications
within range (see figure 5)
–
–
15
%pk-pk
Breduce(NG)
Reduction in VPROC amplitude from VPROC(high)
to lowest peak VPROC(reduce); output switches,
other specifications may be out of range (see
figure 5)
–
–
25
%pk-pk
Maximum Allowable Signal Reduction14
1Typical
values are at TA = 25°C and VCC = 12 V. Performance may vary for individual units, within the specified maximum and minimum limits.
voltage must be adjusted for power dissipation and junction temperature; see Power Derating section.
3Maximum current limit is equal to I (max) + 3 mA.
CC
4Negative current is defined as conventional current coming out of (sourced from) the specified device terminal.
5Power-On Time is the duration from when V
CC rises above VCC(min) until a valid output state is realized.
6Output Delay Time is the duration from when a crossing of the magnetic signal switchpoint, B , occurs to when the electrical output signal, V
ST
OUT ,
reaches 90% of VOUT(high).
7Characterization data shows 12 V fall time to be 1.5 times longer than 5 V fall time. See figure 2.
8The Operational Air Gap Range is the range of installation air gaps within which the TPOS (True Power-On State) function is guaranteed to correctly
detect a tooth when powered-on opposite a tooth and correctly detecting a valley when powered-on opposite a valley, using reference target 8X.
9The Extended Air Gap Range is a range of installation air gaps, larger than AG
TPOS, within which the device will accurately detect target features in
Running Mode, but TPOS functionality is NOT guaranteed, possibly resulting in undetected target features during Initial Calibration. Relative Timing
Accuracy (ErrREL) not guaranteed in Extended Air Gap Range.
10The term mechanical edge refers to a target feature, such as the side of a gear tooth, passing opposite the device. A rising edge is a transition from a
valley to a tooth, and a falling edge is a transition from a tooth to a valley. See figure 7.
11Relative Timing Accuracy refers to the difference in accuracy, relative to a 0.5 mm air gap, through the entire Operational Air Gap Range. See figure 7.
12Refer to Functional Description section for a description of Internal Hysteresis.
13Signal frequency, f
SIG < 200 Hz.
14Running Mode; 4X target used. The Operational Signal Amplitude, V
PROC , is the internal signal generated by the Hall detection circuitry and
normalized by Automatic Gain Calibration.
2Maximum
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
5
ATS675LSE
Self-Calibrating TPOS Speed Sensor
Optimized for Automotive Cam Sensing Applications
Signal Processing Characteristics
VOUT(high)
VOUT(%)
tf
VOUT (V)
VOUT (%)
100
90
10
0
VOUT(low)
Figure 2. Output Rise Time and Output Fall Time
100
90
10
0
td
tf
VPROC(high)
BST
VPROC
tr
VPROC(low)
Figure 3. Output Delay Time and Output Fall Time
Operational
Signal
Amplitude
Switchpoints
VPROC(high)
VPROC(high)
Breduce(G)(max)
Signal
Reduction
Breduce(NG)(max)
VPROC
BHYS
BHYS
VPROC(low)
Full Signal
Processing
VPROC(reduce)
Reduced
Signal
Processing
VPROC
Magnetic Gradient (B)
BST
Lowest peak
VPROC(low)
(Baseline)
0
Figure 4. Switchpoint and Internal Hysteresis
Figure 5. Maximum Allowable Signal Reduction. Breduce for a given tooth
signal is calculated as follows:
Breduce =
Signal Reduction
Operational Signal Amplitude
100%
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
6
Self-Calibrating TPOS Speed Sensor
Optimized for Automotive Cam Sensing Applications
ATS675LSE
Characteristic Performance
OutputSupply
Fall Time
Versusversus
Ambient
Temperature
Current
Supply
Voltage
Supply Current versus Ambient Temperature
RPU = 1 kΩ, C L = 4.7 nF
10
16.00
10
14.00
9
9
8
VCC (V)
7
3.3
15.0
24
TA (°C)
-40
VPU (V)
0
5
25
12
85
150
8
10.00
tf (us)
ICC (mA)
12.00
8.007
6.006
6
4.00
5
5
2.00
4
-50
-25
0
25
50
75
100
TA (°C)
125
150
0.004
0
-50
175
0.3
VOUT(sat) (mV)
300
IOUT (mA)
250
20
15
10
200
150
Edge Position (°)
0.4
350
125
150
TA (°C)
-40
0
25
85
150
-0.4
0.5
175
0.4
0.4
0.3
0.3
0.2
TA (°C)
-40
0
25
85
150
0.1
0
-0.1
-0.2
1
1.5
2
AG (mm)
2.5
3
3.5
Relative Timing Accuracy versus Speed
TA = 25°C, 1.5 mm Air Gap, Relative to 0.5 mm Air Gap
Edge Position (°)
Edge Position (°)
Relative Timing Accuracy versus Air Gap
Rising Mechanical Edge, 1000 rpm, Relative to 0.5 mm Air Gap
0.2
Mechanical
Edge
Falling
Rising
0.1
0
-0.1
-0.2
-0.3
-0.4
0.5
30
175
0
-0.3
75
100
TA (°C)
125 25 150
-0.1
-0.2
50
20
100
0.1
50
25
50 15 75
0.2
100
0
10
25
Relative Timing Accuracy versus Air Gap
Falling Mechanical Edge, 1000 rpm, Relative to 0.5 mm Air Gap
400
-25
0
V
(V)
TCC
A (°C)
Output Voltage (Low) versus Ambient Temperature
0
-50
-25 5
-0.3
1
1.5
2
AG (mm)
2.5
3
3.5
-0.4
0
500
1000
1500
2000
2500
Gear Speed (rpm)
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
7
Self-Calibrating TPOS Speed Sensor
Optimized for Automotive Cam Sensing Applications
ATS675LSE
Reference Target 8x
Test Conditions
Typ.
Units
Do
Outside diameter of target
120
mm
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
23.6
mm
Circular Valley Length
tv
Length of valley, with respect to
sensor; measured at Do
23.6
mm
Tooth Whole Depth
ht
5
mm
–
–
Outside Diameter
Material
Symbol
CRS 1018
Symbol Key
Branded Face
of Sensor
tV
t
Characteristic
ØDO
F
ht
Air Gap
Branded Face
of Sensor
Reference Target 8X
Figure 6. Configuration with Reference Target
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
8
Self-Calibrating TPOS Speed Sensor
Optimized for Automotive Cam Sensing Applications
ATS675LSE
Functional Description
Internal Electronics
This device contains a self-calibrating Hall effect IC that provides
a Hall element, a temperature compensated amplifier, and offset
cancellation circuitry. The IC also contains a voltage regulator
that provides supply noise rejection over the operating voltage
range. The Hall transducers and the electronics are integrated
on the same silicon substrate by a proprietary BiCMOS process.
Changes in temperature do not greatly affect this device, due to
the stable amplifier design and the offset rejection circuitry.
by undervoltage conditions from propagating to the output of the
sensor.
Sensing Technology
The ATS675 gear tooth sensor contains a single-chip Hall effect
sensor IC, a 4-pin leadframe, and a specially designed rare-earth
magnet. The Hall IC supports a chopper stabilized Hall element
that measures the magnetic gradient created by the passing of a
ferrous object. This is illustrated in figure 7. The difference in
the magnetic gradients created by teeth and valleys allows the
devices to generate a digital output signal that is representative of
the target features.
Output
After proper power is applied to the device, it is then capable of
providing digital information that is representative of the profile
of a rotating gear, as illustrated in figure 8. 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.
Undervoltage Lockout
When the supply voltage falls below the undervoltage lockout
level, VCCUV, the device switches to the off-state. The device
remains in that state until the voltage level is restored to the VCC
operating range. Changes in the target magnetic profile have no
effect until voltage is restored. This prevents false signals caused
Power Supply Protection
The ATS675 contains an on-chip regulator and can operate over
a wide range of supply voltage levels. For applications using an
unregulated power supply, transient protection may be added
externally. For applications using a regulated supply line, EMI
and RFI protection may still be required. Contact Allegro for
information on EMC specification compliance.
Output Polarity
With the LT device option, the polarity of the output is low
when the Hall element is opposite a target tooth, and high when
opposite a target valley. The output polarity is opposite in the HT
option.. This is illustrated in figure 8.
TPOS (True Power-On State) Operation
Under specified operating conditions, the ATS675 is guaranteed
Target
Mechanical Profile
Target (Gear)
Target
Magnetic Profile
Low-B field
Hall element
Leadframe
High-B field
Hall IC
North Pole
Back-Biasing
magnet
Plastic
Pole piece
(Concentrator)
South Pole
Tooth Valley
|B|
BIN
Sensor Output
Electrical Profiles
0
V+
VOUT
LT device option
Switch State
On
Off On
Off
On
Off
On
Off
Off
On Off On Off
On
Off
On
Sensor Device
(A)
(B)
V+
HT device option
VOUT
Switch State
Figure 7. Application cross-section: (A) target tooth opposite device, and
(B) target valley opposite device
Figure 8. Sensor output polarity and switch state (with device connected
as shown in figure 1): with LT option, output is low when a target tooth is
opposite the Hall element (device on), and high when a target valley is
opposite (device off)—polarity response inverts with the HT option.
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
9
ATS675LSE
Self-Calibrating TPOS Speed Sensor
Optimized for Automotive Cam Sensing Applications
to attain the specified output voltage polarity at power-on, in
relation to the target feature nearest the device at that time. The
TPOS switchpoint is programmed by Allegro to the datasheet
specifications.
ing accuracy step size during startup conditions. A single large
jump in edge position is not allowed; instead, any change in edge
position from TPOS to Running Mode is spread over several
output transitions.
Start-Up Detection
The ATS675 provides an output polarity transition at the first
target mechanical edge that is opposite the device after power-on.
Switchpoints
The Running Mode switchpoints in the ATS675 are established
dynamically as a percentage of the amplitude of the signal,
VPROC , after normalization with AGC. Two DACs track the
peaks of VPROC.
Calibration
The Automatic Gain Calibration (AGC) feature is implemented
by a unique patented self-calibrating circuitry. After each poweron, the device measures the peak-to-peak magnetic signal. The
gain of the sensor is then adjusted, keeping the internal signal,
VPROC , at a constant amplitude throughout the air gap range of
the device. This feature ensures that operational characteristics
are isolated from the effects of changes in effective air gap. The
Initial Calibration process allows the peak detecting DACs to
properly acquire the magnetic signal, so that a Running Mode
switchpoint can be accurately computed.
TPOS to Running Mode
After the Initial Calibration process is completed (CALI), the
device transitions to Running Mode. As shown in figure 9, the
device dynamically adjusts the relative edge position from the
TPOS edge location to the Running Mode location over several
target teeth (CTPORM), significantly reducing the maximum tim-
TPOS
Threshold
0n 0ff
0ff 0n
Figure 9. Startup calibration order
Peak and Valley DAC Update
The peak and valley DACs have an algorithm that allows tracking of drift over temperature changes, but provides immunity to
target particularities, such as small mechanical valleys.
Running Mode
BST
VPROC
LT option
Switch State
VOUT
HT option
Switch State
VOUT
CALTPOSRM
Internal Hysteresis
The Internal Hysteresis, BHYS , provides high performance over
various air gaps while maintaining immunity to false switching
on noise, vibration, backlash, or other transient events. Figure 10
demonstrates the function of this hysteresis when switching on an
anomalous peak.
BST
BHYS
BHYS
VPROC
Power-on
CALI
The switching threshold is established at a fixed percentage of the
values held in the two DACs. The ATS675 uses a single switching threshold (operate and release points identical) with internal
hysteresis.
LT option
Switch State
VOUT
HT option
Switch State
VOUT
0n
0ff
0ff
0n
Figure 10. Output switching can accommodate an anomalous peak, such
as the middle peak in this figure, by using the Internal Hysteresis value.
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
10
Self-Calibrating TPOS Speed Sensor
Optimized for Automotive Cam Sensing Applications
ATS675LSE
Sensor and Target Evaluation
A pair of curves can be derived from this map data, and be used
to describe the tooth and valley magnetic field strength, B, versus
the size of the air gap, AG. This allows determination of the minimum amount of magnetic flux density that guarantees operation
of the sensor, so the system designer can determine the maximum
allowable AG for the sensor and target system. One can also
determine the TPOS air gap capabilities of the sensor by comparing the minimum tooth signal to the maximum valley signal.
Magnetic Profile
In order to establish the proper operating specification for a particular sensor device and target system, a systematic evaluation
of the magnetic circuit should be performed. The first step is the
generation of a magnetic map of the target. By using a calibrated
device, a magnetic profile of the system is made. Figure 11 is a
magnetic map of the 8X reference target.
Magnetic Map, Reference Target 8X with SE Package
1600
1400
Flux Density, B (G)
1200
1000
800
600
400
200
0
0
60
120
180
240
300
360
Target Rotation (°)
Air Gap Versus Magnetic Field, Reference Target 8X with SE Package
1300
1200
1100
Flux Density, B (G)
1000
900
800
700
600
500
Tooth
400
Valley
300
200
100
0
0
1.0
2.0
3.0
4.0
5.0
6.0
AG (mm)
Figure 11. Magnetic Data for the 8X Reference Target and SE package. Flux
density measurements are relative to the baseline magnetic field.
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
11
ATS675LSE
Self-Calibrating TPOS Speed Sensor
Optimized for Automotive Cam Sensing Applications
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, 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)
For example, given common conditions such as: TA= 25°C,
VCC = 12 V, ICC = 7 mA, and RθJA = 77 °C/W, then:
Example: Reliability for VCC at TA = 150°C.
Observe the worst-case ratings for the device, specifically:
RθJA = 101 °C/W, TJ(max) = 165°C, VCC(max) = 24 V, and
ICC(max) = 10 mA.
Calculate the maximum allowable power level, PD(max). First,
invert equation 3:
ΔT(max) = 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) = ΔT(max) ÷ RθJA = 15°C ÷ 101 °C/W = 148.5 mW
Finally, invert equation 1 with respect to voltage:
VCC(est) = PD(max) ÷ ICC(max) = 148.5 mW ÷ 10 mA = 14.9 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.
PD = VCC × ICC = 12 V × 7 mA = 84 mW
ΔT = PD × RθJA = 84 mW × 77 °C/W = 6.5°C
TJ = TA + ΔT = 25°C + 6.5°C = 31.5°C
A worst-case estimate, PD(max), represents the maximum allowable power level, without exceeding TJ(max), at a selected
RθJA and TA.
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
12
Self-Calibrating TPOS Speed Sensor
Optimized for Automotive Cam Sensing Applications
ATS675LSE
Package SE 4-Pin SIP Module
1.5
7.00
C
10.00
1.5
B
3.3
E
1.3
0.9
5.7
A
4.9
6.2
0.38
24.65
11.6
1
2
3
All dimensions nominal, not for tooling use
Dimensions in millimeters
Exact case and lead configuration at supplier
discretion within limits shown
4
A Dambar removal protrusion (16X)
2.0
0.6
B Metallic protrusion, electrically connected to pin 4 and substrate (both sides)
C Active Area Depth, 0.43 mm
D Thermoplastic Molded Lead Bar for alignment during shipment
E Hall element (not to scale)
A
D
1.6
1.27
0.7
0.7
5.5
Copyright ©2008, 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 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
13
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