A1642 Datasheet

A1642
Two-Wire True Zero-Speed Miniature Differential
Peak-Detecting Sensor IC with Continuous Calibration
Features and Benefits
Description
▪ Running mode calibration for continuous optimization
▪ Single chip IC for high reliability
▪ Internal current regulator for 2-wire operation
▪ Precise duty cycle signal over operating temperature range
▪ Large operating air gaps
▪ Automatic Gain Control (AGC) for air gap independent
switchpoints
▪ Automatic Offset Adjustment (AOA) for signal processing
optimization
▪ True zero-speed operation
▪ Undervoltage lockout
▪ Wide operating voltage range
▪ Wide-lead package suitable for welding external
components directly to the package leads or for welding
the device to a leadframe.
The A1642 is an optimized Hall effect sensing integrated
circuit that provides a user-friendly solution for true zero-speed
digital ring-magnet sensing in two-wire applications. This small
package can be easily assembled and used in conjunction with
a wide variety of target shapes and sizes.
Package: 4-pin SIP (Suffix KN)
The integrated circuit incorporates dual Hall effect elements
and signal processing that switches in response to differential
magnetic signals created by ring magnet poles. The circuitry
contains a sophisticated digital circuit to reduce system offsets,
to calibrate the gain for air-gap–independent switchpoints,
and to achieve true zero-speed operation. Signal optimization
occurs at power-on through the combination of offset and
gain adjust and is maintained throughout the operating time
with the use of a running-mode calibration. The running-mode
calibration allows immunity to environmental effects such as
micro-oscillations of the target or sudden air gap changes.
The regulated current output is configured for two-wire
applications and the A1642 is ideally suited for obtaining
speed and duty cycle information in ABS (antilock braking
systems). The 1.5 mm spacing between the dual Hall elements
is optimized for fine pitch ring-magnet–based configurations.
For applications requiring sensing of rotating ferrous gears and
targets, refer to the Allegro ATS series of products. The package
is lead (Pb) free, with 100% matte tin leadframe plating.
Not to scale
Functional Block Diagram
Hall
Amplifier
Automatic Offset
Control
VCC
Gain
AOA DAC
AGC DAC
Internal Regulator
Gain Control
Tracking
DAC
Peak Hold
GND
Test Signals
A1642LKN-DS, Rev. 4
Test
Two-Wire True Zero-Speed Miniature Differential
Peak-Detecting Sensor IC with Continuous Calibration
A1642
Selection Guide
Part Number
ICC Range
Packing*
A1642LKNTN-I1-T
4.0 mA Low to 16.0 mA High
A1642LKNTN-I2-T
5.9 mA Low to 16.8 mA High
A1642LKNTN-I3-T
5.9 mA Low to 16.0 mA High
Tape and reel, 13-inch reel
4000 pieces per reel
*Contact Allegro for additional packing options
Absolute Maximum Ratings
Characteristic
Symbol
Supply Voltage
VCC
Reverse Supply Voltage
VRCC
Notes
Rating
Units
28
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
Range L
Pin-out Diagram
Terminal List Table
Number
1 2 3 4
Name
Function
1
VCC
Connects power supply to chip
2
NC
No connection
3
Test
Float or tie to GND
4
GND
Ground connection
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115 Northeast Cutoff
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A1642
Two-Wire True Zero-Speed Miniature Differential
Peak-Detecting Sensor IC with Continuous Calibration
OPERATING CHARACTERISTICS TA and VCC within specification, unless otherwise noted
CHARACTERISTIC
Min.
Typ.1
Max.
Units
4.0
–
24
V
VCC 0 → 5 V and 5 → 0 V
–
–
4.0
V
Symbol
Test Conditions
ELECTRICAL CHARACTERISTICS
Supply Voltage2
Undervoltage Lockout
VCC
VCC(UV)
Operating; TJ < 165°C
Supply Zener Clamp Voltage
VZ
ICC = ICC(max) + 3 mA; TA = 25°C
28
–
–
V
Supply Zener Current
IZ
Test conditions only; VZ = 28 V
–
–
ICC(max)+
3 mA
mA
A1642LKN-I1
4.0
6.0
8.0
mA
A1642LKN-I2, A1642LKN-I3
5.9
7.0
8.4
mA
A1642LKN-I1, A1642LKN-I3
12.0
14.0
16.0
mA
A1642LKN-I2
11.8
14.0
16.8
mA
1.85
–
3.05
–
VRCC = –18 V
–
–
–5
mA
t > tPO
–
ICC(High)
–
–
ICC(Low)
Supply Current
ICC(High)
Supply Current Ratio
Reverse Battery Current
ICC(High)/ Ratio of high current to low current
ICC(Low)
IRCC
POWER-ON STATE CHARACTERISTICS
Power-On State3
POS
Power-On Time4
tPO
fOP < 100 Hz
–
1
2
ms
dI/dt
RLOAD = 100 Ω, CLOAD = 10 pF
–
14
–
mA/μs
OUTPUT STAGE
Output Slew Rate5
Continued on the next page.
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115 Northeast Cutoff
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A1642
Two-Wire True Zero-Speed Miniature Differential
Peak-Detecting Sensor IC with Continuous Calibration
OPERATING CHARACTERISTICS (continued) TA and VCC within specification, unless otherwise noted
Characteristic
Symbol
Min.
Typ.1
Max.
Units
0
–
8,000
Hz
20
40
–
kHz
–
120
–
mV
–
120
–
mV
Quantity of rising output (current) edges required for
accurate edge detection
–
–
3
Edge
Operating within specification
–
–
±90
G
Operating within specification
30
–
1000
G
Output switching (no missed edges); ∆DC not
guaranteed
20
–
–
G
Test Conditions
SWITCHPOINT CHARACTERISTICS
Operating Speed
fOP
Analog Signal Bandwidth
BW
Operate Point
BOP
Release Point
BRP
Equivalent to f – 3 dB
Transitioning from ICC(High) to ICC(Low); positive peak
referenced; AG < AGMAX
Transitioning from ICC(Low) to ICC(High); negative peak
referenced; AG < AGMAX
CALIBRATION
Initial Calibration
CI
DAC CHARACTERISTICS
Allowable User-Induced Differential
Offset
FUNCTIONAL CHARACTERISTICS6
Operating Signal Range7
Minimum Operating Signal
Sig
SigOP(min)
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.
3Please refer to Device Operation section.
4Power-On Time includes the time required to complete the internal automatic offset adjust. The DAC is then ready for peak acquisition.
5dI is the difference between 10% of I
CC(Low) and 90% of ICC(High), and dt is the time period between those two points.
Note: dI/dt is dependent upon the value of the bypass capacitor, if one is used.
6Functional characteristics valid only if magnetic offset is within the specified range for Allowable User Induced Differential Offset.
7In order to remain in specification, the magnetic gradient must induce an operating signal greater than the minimum value specified. This includes the
effect of target wobble.
2Maximum
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Two-Wire True Zero-Speed Miniature Differential
Peak-Detecting Sensor IC with Continuous Calibration
A1642
Characteristic Data
Supply Current (High) versus Supply Voltage
(I1 Trim)
16
16
15
15
Vcc (V)
24
12
4
14
ICC(HIGH) (mA)
ICC(HIGH) (mA)
Supply Current (High) versus Ambient Temperature
(I1 Trim)
TA (°C)
-40
25
85
150
14
13
13
12
12
-50
0
50
100
0
150
5
10
TA (°C)
Supply Current (Low) versus Ambient Temperature
(I1 Trim)
20
25
Supply Current (Low) versus Supply Voltage
(I1 Trim)
8
8
7
7
Vcc (V)
24
12
4
6
ICC(LOW) (mA)
ICC(LOW) (mA)
15
VCC (V)
TA (°C)
-40
25
150
6
5
5
4
4
-50
0
50
TA (°C)
100
150
0
5
10
15
20
25
VCC (V)
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Two-Wire True Zero-Speed Miniature Differential
Peak-Detecting Sensor IC with Continuous Calibration
A1642
Characteristic Allowable Air Gap Movement
Allowable Air Gap Movement from TEAGCAL*
1.2
ΔTEAGOUT (mm)
1.0
0.8
0.6
0.4
0.2
0
-0.2
0
0.2
0.4
0.6
0.8
1.0
ΔTEAGIN (mm)
1.2
1.4
1.6
1.8
*Data based on study performed using spur gear reference target 60-0, and
applicable to ring magnet targets with similar magnetic characteristics.
The axis parameters for the chart are defined in the drawings
below. As an example, assume the case where the air gap is
allowed to vary from the nominal installed air gap (TEAGCAL ,
panel a) within the range defined by an increase of TEAGOUT =
0.35 mm (shown in panel b), and a decrease of TEAGIN =
0.65 mm (shown in panel c). This case is plotted with an “x” in
the chart above.
The colored area in the chart above shows the region of allowable air gap movement within which the device will continue
output switching. The output duty cycle is wholly dependent on
the target’s magnetic signature across the air gap range of movement, and may not always be within specification throughout the
entire operating region (to AG(OPmax)).
(a)
(b)
A1642
(c)
A1642
TEAGCAL
TEAG OUT
TEAG IN
A1642
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Two-Wire True Zero-Speed Miniature Differential
Peak-Detecting Sensor IC with Continuous Calibration
A1642
THERMAL CHARACTERISTICS may require derating at maximum conditions, see application information
CHARACTERISTIC
Symbol
TEST CONDITIONS*
RθJA
Package Thermal Resistance
Single-layer PCB with copper limited to solder pads
Value
Units
170
ºC/W
*Additional information is available on the Allegro Web site.
Maximum Allowable VCC (V)
Power Derating Curve
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 = 170 ºC/W)
VCC(min)
20
40
60
80
100
120
140
160
180
Ambient Temperature, TA (ºC)
Power Dissipation versus Ambient Temperature
1300
1200
1000
900
800
(R
700
QJ
A
=
17
600
0
ºC
/W
500
)
Power Dissipation, PD (m W)
1100
400
300
200
100
0
20
40
60
80
100
120
140
Ambient Temperature, TA (°C)
160
180
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115 Northeast Cutoff
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Two-Wire True Zero-Speed Miniature Differential
Peak-Detecting Sensor IC with Continuous Calibration
A1642
Functional Description
Sensing Technology
The single-chip differential Hall effect sensor IC possesses two
Hall elements, which sense the magnetic profile of the ring magnet simultaneously, but at different points (spaced at a 1.5 mm
pitch), generating a differential internal analog voltage, VPROC ,
that is processed for precise switching of the digital output
signal.
The Hall IC is self-calibrating and also possesses a temperature
compensated amplifier and offset compensation circuitry. Its
voltage regulator provides supply noise rejection throughout the
operating voltage range. Changes in temperature do not greatly
affect this device due to the stable amplifier design and the offset
compensation circuitry. The Hall transducers and signal processing electronics are integrated on the same silicon substrate, using
a proprietary BiCMOS process.
Target Profiling
An operating device is capable of providing digital information that is representative of the magnetic features on a rotating
target. The waveform diagram shown in figure 3 presents the
automatic translation of the magnetic profile to the digital output
signal of the device.
Output Polarity
Figure 3 shows the output polarity for the orientation of target
and device shown in figure 2. The target direction of rota-
tion shown is: perpendicular to the leads, across the face of the
device, from the pin 1 side to the pin 4 side. This results in the
device output switching from high, ICC(High), to low ICC(Low),
as the leading edge of a north magnetic pole passes the device
face. In this configuration, the device output current switches to
its low polarity when a north pole is the target feature nearest to
the device. If the direction of rotation is reversed, then the output
polarity inverts.
Note that output voltage polarity is dependent on the position of
the sense resistor, RSENSE (see figure 4).
Target
Ring Magnet
N
S
S
N
Representative
Differential
Magnetic Profile
Device Electrical
Output Profile, IOUT
Figure 3. Output Profile of a ring magnet target for the polarity
indicated in figure 2.
VSUPPLY
VCC
RSENSE
Target
(Ring Magnet)
ICC
S
N
N
S
VOUT(H)
Element Pitch
Hall Element 2
Hall Element 1
Hall IC
(Pin 4 Side)
1
1
VCC
VCC
A1642
A1642
GND
4
GND
4
(Pin 1 Side)
VOUT(L)
Figure 1. Relative motion of the target is detected by the dual Hall elements mounted on the Hall IC.
ICC
RSENSE
Branded Face
of Device
Rotating Target
I+
IOUT
V+
1
4
VOUT(L)
V+
Figure 2. This left-to-right (pin 1 to pin 4) direction of target rotation
results in a low output signal when a magnetic north pole of the target is
nearest the face of the device (see figure 3). A right-to-left (pin 4 to pin
1) rotation inverts the output signal polarity.
VOUT(H)
Figure 4: Voltage profiles for high side and low side two-wire sensing.
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Two-Wire True Zero-Speed Miniature Differential
Peak-Detecting Sensor IC with Continuous Calibration
A1642
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). During calibration, the device determines the peak-topeak amplitude of the signal generated by the target. The gain of
the device is then automatically adjusted. Figure 5 illustrates the
effect of this feature.
Automatic Offset Adjust (AOA)
The AOA is patented circuitry that automatically compensates
for the effects of chip, magnet, and installation offsets. (For
capability, see Dynamic Offset Cancellation, in the Operating Characteristics table.) This circuitry is continuously active,
including both during calibration mode and running mode,
compensating for offset drift. Continuous operation also allows
Target
Ring Magnet
N
S
N
Digital Peak Detection
A digital DAC tracks the internal analog voltage signal VPROC,
and is used for holding the peak value of the internal analog
signal. In the example shown in figure 6, the DAC would first
track up with the signal and hold the upper peak’s value. When
VPROC drops below this peak value by BOP, the device hysteresis, the output would switch and the DAC would begin tracking
the signal downward toward the negative VPROC peak. Once the
DAC acquires the negative peak, the output will again switch
states when VPROC is greater than the peak by the value BRP. At
this point, the DAC tracks up again and the cycle repeats. The
digital tracking of the differential analog signal allows the device
to achieve true zero-speed operation.
S
V+
Internal Differential
Analog Signal
Response, without AGC
it to compensate for offsets induced by temperature variations
over time.
V+
AGLarge
Internal
Differential
Analog Signal
BOP
BRP
AGSmall
V+
Internal Differential
Analog Signal
Response, with AGC
I+
AGSmall
AGLarge
Figure 5. Automatic Gain Control (AGC). The AGC function corrects for
variances in the air gap. Differences in the air gap affect the magnetic
gradient, but AGC prevents that from affecting device performance, as
shown in the lowest panel.
Device
Output Current
Figure 6: Peak Detecting Switchpoint Detail
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Two-Wire True Zero-Speed Miniature Differential
Peak-Detecting Sensor IC with Continuous Calibration
A1642
Power Supply Protection
Assembly Description
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
This device 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.
application circuit.
Undervoltage Lockout
When the supply voltage falls below the undervoltage lockout
voltage, VCC(UV), the device enters Reset, where the output state
returns to the Power-On State (POS) until sufficient VCC is supplied. ICC levels may not meet datasheet limits when
VCC < VCC(min).
Diagnostics
The regulated current output is configured for two wire applications, requiring one less wire for operation than do switches
with the more traditional open-collector output. Additionally,
the system designer inherently gains diagnostics because there is
always output current flowing, which should be in either of two
narrow ranges, shown in figure 8 as ICC(High) and ICC(Low). Any
current level not within these ranges indicates a fault 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.
V+
1
VCC
A1642
Pins 2 and 3 floating
GND
4
CBYP
0.01 µF
+mA
ICC(High)max
Short
ICC(High)min
ICC(Low)max
ECU

Range for Valid ICC(HIGH)

Range for Valid ICC(LOW)
Fault
ICC(Low)min
Open
100 Ω
RSENSE
Figure 7: Typical Application Circuit
0
Figure 8: Diagnostic Characteristics of Supply Current Values
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Two-Wire True Zero-Speed Miniature Differential
Peak-Detecting Sensor IC with Continuous Calibration
A1642
AGC is active, and selects the optimal signal gain based on the
amplitude of the VPROC signal. Following each adjustment to
the AGC DAC, the Offset DAC is also adjusted to ensure the
internal analog signal is properly centered.
DEVICE OPERATION
Each operating mode is described in detail below.
Power-On
When power (VCC > VCC(Min)) is applied to the device, a short
period of time is required to power the various portions of the
IC. During this period, the A1642 powers-on in the high current
state, ICC(High). After power-on, there are conditions that could
induce a change in the output state. Such an event could be
caused by thermal transients, but would require a static applied
magnetic field, proper signal polarity, and particular direction
and magnitude of internal signal drift.
During this mode, the tracking DAC is active and output switching occurs, but the duty cycle is not guaranteed to be within
specification.
Running Mode
After the Initial Calibration period, CI, establishes a signal gain,
the device moves to Running mode. During Running mode, the
device tracks the input signal and gives an output edge for every
peak of the signal. AOA remains active to compensate for any
offset drift over time.
Initial Offset Adjust
The device initially cancels the effects of chip, magnet, and
installation offsets. Once offsets have been cancelled, the digital
tracking DAC is ready to track the signal and provide output
switching. The period of time required for both Power-On and
Initial Offset Adjust is defined as the Power-On Time.
The A1642 incorporates a novel algorithm for adjusting the
signal gain during Running mode. This algorithm is designed
to optimize the VPROC signal amplitude in instances where the
magnetic signal “seen” during the calibration period is not representative of the amplitude of the magnetic signal for the installed
device air gap (see figure 9).
Calibration Mode
The calibration mode allows the device to automatically select
the proper signal gain and continue to adjust for offsets. The
1
2
3
4
5
BOP
Internal Differential
Signal, VPROC
BOP
BRP
BRP
Device Electrical
Output, IOUT
Figure 9: Operation of Running Mode Gain Adjust.
Position 1. The device is initially powered-on. Self-calibration occurs.
Position 2. Small amplitude oscillation of the target sends an erroneously small differential signal to the device. The amplitude of VPROC is greater than the switching hysteresis (BOP and BRP), and the device output switches.
Position 3. The calibration period completes on the third rising output edge, and the device enters Running mode.
Position 4. True target rotation occurs and the correct magnetic signal is generated for the installation air gap. The established signal gain is too large for the target’s rotational magnetic signal at the given air gap.
Position 5. Running Mode Calibration corrects the signal gain to an optimal level for the installation air gap.
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Two-Wire True Zero-Speed Miniature Differential
Peak-Detecting Sensor IC with Continuous Calibration
A1642
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, 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

T = PD × RJA
TJ = TA + ΔT
(1)
(2)
Example: Reliability for VCC at TA = 150°C, package KN
(I1 trim), using 1-layer PCB
Observe the worst-case ratings for the device, specifically:
RJA = 170 °C/W, TJ(max) = 165°C, VCC(max) = 24 V, and
ICC(max) = 16 mA.
Calculate the maximum allowable power level, PD(max). First,
invert equation 3:
Tmax = TJ(max) – TA = 165 °C – 150 °C = 15 °C
This provides the allowable increase to TJ resulting from internal
power dissipation. Then, invert equation 2:
PD(max) = Tmax ÷ RJA = 15°C ÷ 170 °C/W = 88.2 mW
Finally, invert equation 1 with respect to voltage:
VCC(est) = PD(max) ÷ ICC(max) = 88.2 mW ÷ 16 mA = 5.5 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.
(3)
For example, given common conditions such as: TA= 25°C,
VCC = 12 V, ICC = 6 mA, and RJA = 170 °C/W, then:
PD = VCC × ICC = 12 V × 6 mA = 72 mW

T = PD × RJA = 72 mW × 170 °C/W = 12.2°C
TJ = TA + T = 25°C + 12.2°C = 37.2°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.
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12
Two-Wire True Zero-Speed Miniature Differential
Peak-Detecting Sensor IC with Continuous Calibration
A1642
Package KN, 4-Pin SIP
+0.08
5.21 –0.05
45°
B
E
E
1.50
1.85
D
1.55 ±0.05
Mold Ejector
Pin Indent
1.32 E
+0.08
3.43 –0.05
E1
E2
Branded
Face
2.16
MAX
45°
0.84 REF
NNNN
YYWW
6.00
REF
A
+0.07
0.41 –0.05
1
2
3
C
N = Device part number
Y = Last two digits of year of manufacture
W = Week of manufacture
4
14.74 ±0.51
1.27 NOM
+0.08
1.03 –0.05
8.12 REF
1
Standard Branding Reference View
+0.06
0.38 –0.03
For Reference Only; not for tooling use (reference DWG-9015)
Dimensions in millimeters
Dimensions exclusive of mold flash, gate burrs, and dambar protrusions
Exact case and lead configuration at supplier discretion within limits shown
A Dambar removal protrusion (8X)
B Gate and tie bar burr area
C
0.38
REF
Branding scale and appearance at supplier discretion
D
Active Area Depth 0.43 mm REF
E
Hall elements (E1,E2), not to scale
3.19 NOM
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1.508.853.5000; www.allegromicro.com
13
A1642
Two-Wire True Zero-Speed Miniature Differential
Peak-Detecting Sensor IC with Continuous Calibration
Revision History
Revision
Revision Date
Rev. 4
January 16, 2012
Description of Revision
Update product variants offered
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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
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Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
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