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A1425
High Accuracy Analog Speed Sensor with Integrated Filter Capacitor and Dual Zero-Crossing Output Signal
The A1425 ac-coupled Hall-effect sensor is a monolithic integrated circuit that switches in response to changing differential magnetic fields created by rotating ring magnets and, when coupled with a magnet, by ferrous targets. The device is a true zero-crossing detector: the output switches precisely when the difference in magnetic field strength between the two Hall elements is zero. A unique dual-comparator scheme provides for accurate switching at the zero crossing on both the positive and negative-going regions of the differential signal, while utilizing hysteresis to prevent false switching. The zero-crossing nature of this device provides excellent repeatability and accuracy for crankshaft applications. Changes in field strength at the device face, which are induced by a moving target, are sensed by the two integrated Hall transducers. The transducers generate signals that are differentially amplified by on-chip electronics. This differential sensing design provides immunity to radial vibration within the operating air gap range of the A1425, by rejection of the common mode signal. Steady-state magnet and system offsets are eliminated using an on-chip differential band-pass filter. This filter also provides relative immunity to interference from electromagnetic sources. The device utilizes advanced temperature compensation for the high-pass filter, sensitivity, and Schmitt trigger switchpoints, to guarantee optimal operation to low frequencies over a wide range of air gaps and temperatures.
1 2 3 4
Package K, 4-pin SIP
1. VCC 2. VOUT 3. TEST 4. GND
Each Hall effect digital integrated circuit includes a voltage regulator, two Hall effect sensing elements, temperature compensating circuitry, a low-level amplifier, band-pass filter, Schmitt trigger, and an output driver, which requires a pull-up resistor. The on-board regulator permits operation with supply voltages from 4.0 to 26.5 V. The output stage can easily switch 20 mA over the full frequency response range of the sensor, and is compatible with both TTL and CMOS logic circuits. The device is packaged in a 4-pin plastic SIP. The lead (Pb) free version (suffix -T) has a 100% matte tin plated leadframe.
ABSOLUTE MAXIMUM RATINGS
Supply Voltage*, VCC ........................................ 28 V Reverse-Supply Voltage, VRCC ........................ -18 V Continuous Output Current, IOUT ...................25 mA Continuous Reverse-Output Current, IROUT .-50 mA Operating Temperature Ambient, TA................................ -40C to 150C Maximum Junction, TJ(max)........................165C Storage Temperature, TS .................. -65C to 170C *Refer to Power Derating section.
Features and Benefits
* * * * * * * * * * * Senses motion of ring magnet or ferrous targets Integrated filter capacitor Wide operating temperature range
Resistant to EMI Large effective air gaps 4.0 to 26.5 V supply operating range Output compatible with both TTL and CMOS logic families Reverse battery protection Resistant to mechanical and thermal stress Accurate true zero crossing switchpoint
Operation with magnetic input signal frequency from 20 Hz to 20 kHz
A1425a-DS
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
A1425
High Accuracy Analog Speed Sensor with Integrated Filter Capacitor and Dual Zero-Crossing Output Signal
Product Selection Guide
Switchpoints BRP(MIN) (G) -11 BOP(MAX) (G) 11 Packing2 Bulk, 500 pieces/bag
Part Number A1425LK-T
1Pb-based
Pb-free1 Yes
Ambient, TA (C) -40 to 150
variants are being phased out of the product line. These variants are in production but have been determined to be NOT FOR NEW DESIGN. This classification indicates that sale of this device is currently restricted to existing customer applications. The device should not be purchased for new design applications because obsolescence in the near future is probable. Samples are no longer available. Status change: May 1, 2006. This includes: A1425LK.
2Contact Allegro
for additional packing options
Functional Block Diagram
VS+ VCC (Pin 1) Diagnostic Circuitry Bandpass Filter Integrated Tracking Capacitor Comparator 0.1 uF Hall Amp Gain Stage VREF VOUT (Pin 2) TEST (Pin 3)
Regulator Dual Hall Transducers
GND (Pin 4)
(Required)
A1425-DS
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
2
A1425
High Accuracy Analog Speed Sensor with Integrated Filter Capacitor and Dual Zero-Crossing Output Signal
OPERATING CHARACTERISTICS Valid at TA = - 40C to 150C, TJ 165C; over operational air gap range and VCC within operating range, unless otherwise noted. Typical operating parameters: VCC = 12 V and TA = 25C.
Characteristic ELECTRICAL CHARACTERISTICS Supply Voltage Supply Current Output Saturation Voltage Output Leakage Current VCC ICC VOUT(SAT) ISINK = 20 mA IOFF VOUT = 24 V, Bdiff = 0 Operating; TJ < TJ(max) 4.0 - - - - 4.2 140 - 26.5 7.0 400 5 V mA mV A Symbol Test Conditions Min. Typ. Max. Units
PROTECTION COMPONENT CHARACTERISTICS Reverse Supply Current Supply Zener Current Supply Zener Clamp Voltage1 Output Zener Current Output Zener Clamp Voltage Output Short Circuit Current Limit2 IRCC IZSupply VZSupply IZOutput VZOutput IOUTS(lim) POS tPO tSettle fcu fcl tr tf BOP BRP Bdiff t < tResponse VCC > VCC(min) fBdiff 100 Hz -3 dB, single pole -3 dB, single pole RPU = 1 k, COUT2 = 10 pF RPU = 1 k, ISINK = 20 mA, COUT2 = 10 pF Bdiff increasing, fBdiff = 200 Hz, Bdiff = 50 Gp-p; digital output signal switches low to high Bdiff decreasing, fBdiff = 200 Hz, Bdiff = 50 Gp-p; digital output signal switches high to low Differential p-p magnetic field VCC = -18 V VS = 28 V ICC = 10 mA, TA = 25C VOUT = 28 V IOUT = 3 mA, TA = 25C - - 28 - 28 - - - 33 - - - -1 10 37 3 - 50 mA mA V mA V mA
RESPONSE CHARACTERISTICS Power-On State Power-On Settling Time3,7 - - 0 4.5 20 - - - High 4.5 - - - - - - - 9 50 59 - 20 200 200 V ms ms ms kHz Hz ns ns
Time4,7
Response Time7 Upper Corner Frequency Lower Corner Frequency OUTPUT CHARACTERISTICS Output Rise Time5 Output Fall Time MAGNETIC CHARACTERISTICS Output Off Switchpoint6,7 Output On Switchpoint6,7 Applied Magnetic Field7,8
1I
CC equivalent to ICC(max) + 3 mA. 2I OUT does not change state when IOUT 3Time required to initialize device. 4Time 5Output
tResponse Equal to tPO + tS; fBdiff 100 Hz
-11 -11 50
0 0 -
11 11 1250
G G G
> IOUTS(lim) , regardless of changes in the sensed magnetic field..
required for the output switchpoints to be within specification. Rise Time will be dominated by the RC time constant. 6For other sinusoidal signal frequencies and magnetic fields, -B OP = BRP = sin(Bdiff 2) 25%, where is the phase shift shown in the Characteristic Data section. 7See Definitions of Terms section. 8Exceeding the maximum magnetic field may result in compromised absolute accuracy.
A1425-DS
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
3
A1425
High Accuracy Analog Speed Sensor with Integrated Filter Capacitor and Dual Zero-Crossing Output Signal
THERMAL CHARACTERISTICS may require derating at maximum conditions, see application information
Characteristic Package Thermal Resistance Symbol RJA Test Conditions Single-layer PCB, with copper limited to solder pads Rating Units 177 C/W
Power Derating Curve
30 28 26
900 850
Maximum Power Dissipation, PD(max)
VCC(max)
800 750 700 650 600 550 500 450 400 350 300 250 200 150 100 50 0
Maximum Allowable VCC (V)
24 22
Power Dissipation, PD (m W)
20 18 16 14 12 10 8 6 4 2 0 20 40 60 80 100 120 140 160 180
(R
J
A
=
(RJA = 177 C/W)
17
7
C
/W
)
VCC(min)
20
40
60
80
100
120
140
160
180
Temperature (C)
Temperature (C)
Definitions of Terms The following provide additional information about some of the parameters cited in the Operating Characteristics table. For additional information, visit the Allegro Web site at www.allegromicro.com. Applied Magnetic Field, Bdiff - The differential magnetic flux density which is calculated as the arithmetic difference of the flux densities observed by each of the two Hall elements. Output Off Switchpoint (Operate Point), BOP - The value of increasing differential magnetic flux density at which the device output switches from low to high. This value may be greater than or less than 0 G. Output On Switchpoint (Release Point), BRP - The value of decreasing differential magnetic flux density at which the device output switches from high to low. This value may be greater than or less than 0 G. Power-On Time, tPO - The time needed by the device, after power is applied, to initialize all circuitry necessary for proper operation. Settling Time, tSettle - The time required by the device, after tPO, and after a valid magnetic signal has been applied, to provide proper output transitions. Settling time is a function of magnetic offset, offset polarity, signal phase, signal frequency, and signal amplitude. Response Time tResponse - The total time required for generating zero-crossing output transitions after power-up (the sum of power-on time and settling time).
A1425-DS
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
4
A1425
High Accuracy Analog Speed Sensor with Integrated Filter Capacitor and Dual Zero-Crossing Output Signal
Empirical Results
Supply Current by Ambient Temperature
7 6 5 ICC (mA) 4 3 2 1 0 -50 0 50 TA (C) 100 150 200
VCC (V)
Output Voltage by Ambient Temperature
500 450 400 350 300 250 200 150 100 50 0 -50 ISINK = 20 mA
VCC (V)
4.5 12.0 20.0
VOUT(SAT) (mV)
4.5 12 12.0 26 20.0
0
50 TA (C)
100
150
200
Supply Current by Supply Voltage
7 6 5 ICC (mA) 4 3 2 1 0 0 10 VCC (V) 20 30
TA (C)
Output Voltage by Supply Voltage
500 450 400 350 300 250 200 150 100 50 0 0 ISINK = 20 mA
TA (C)
150 25 -40
VOUT(SAT) (mV)
150 25 -40
5
10 VCC (V)
15
20
25
Continued on next page.
A1425-DS
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
5
A1425
High Accuracy Analog Speed Sensor with Integrated Filter Capacitor and Dual Zero-Crossing Output Signal
Empirical Results, continued
116
Repeatability ( of Rotation)
Air Gap (mm)
116
Repeatability ( of Rotation)
Air Gap (mm)
A1425-DS
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
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A1425
High Accuracy Analog Speed Sensor with Integrated Filter Capacitor and Dual Zero-Crossing Output Signal
Simulation Results
A1425 Minimum Switching Fields Over the Range of Ambient Operating Temperatures, TA fBdiff(low) = 15 Hz, fBdiff(high) 30 kHz 40 35 30 25 Bdiff(min) (G) 20 -40 15 10 5 0 0.01
25
150
0.1
1 Frequency, fBdiff (kHz)
10
40
A1425 Typical Phase Shift Over the Range of Applied Magnetic Fields, Bdiff fBdiff(low) = 15 Hz, fBdiff(high) = 30 kHz 40 30 20
50 100 500 10 750
Phase Shift () 0 -10 -20 -30 -40 -50 -60 0.01 40
1250
Bdiff in Gp-p
0.1
1 Frequency, fBdiff (kHz)
10
Continued on next page.
A1425-DS
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
7
A1425
High Accuracy Analog Speed Sensor with Integrated Filter Capacitor and Dual Zero-Crossing Output Signal
Simulation Results, continued
A1425 Typical Delay Over the Range of Applied Magnetic Fields, Bdiff fBdiff(low) = 15 Hz, fBdiff(high) = 30 kHz 20 IOUT Leading 15 10 5 0 IOUT Lagging -5 -10 -15 -20 0.1 1 Frequency, fBdiff (kHz) 10 40
Bdiff in Gp-p
IOUT Delay (s)
75
0
12
50
50 0
Positive values of delay indicate a lagging output, while negative values indicate a leading output.
IOUT Leading
1000 0 -1000 -2000 -3000
Bdiff in Gp-p
IOUT Delay (s)
IOUT Lagging
-4000
50 100
A1425 Typical Delay Over the Range of Applied Magnetic Fields, Bdiff fBdiff(low) = 15 Hz, fBdiff(high) = 30 kHz
1250 750
500
10
-5000 -6000 0
0
50
100 Frequency, fBdiff (Hz)
Positive values of delay indicate a lagging output, while negative values indicate a leading output.
A1425-DS
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
8
A1425
High Accuracy Analog Speed Sensor with Integrated Filter Capacitor and Dual Zero-Crossing Output Signal
Sensor Evaluation: EMC Characterization
Please contact Allegro MicroSystems for EMC performance information.
Test Name ESD - Human Body Model* ESD - Machine Model* Conducted Transients Direct RF Injection Bulk Current Injection TEM Cell Reference Specification AEC-Q100-002 AEC-Q100-003 ISO 7637-1 ISO 11452-7 ISO 11452-4 ISO 11452-3
*ESD testing is performed with no external components.
Vs
R1
C1
1 VCC
RPU
2
4
GND
1425
VOUT
COUT2
TEST 3
(Required)
Recommended EMC test circuit.
Component RPUa R1b C1 COUT2c
Value 1.2 100 0.1 4.7
Units k F nF
aPull-up resistor not required for protection but for normal operation. bFor improved CI performance cFor improved BCI performance
A1425-DS
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
9
A1425
High Accuracy Analog Speed Sensor with Integrated Filter Capacitor and Dual Zero-Crossing Output Signal
Functional Description
The A1425 is a versatile high-precision differential sensing device that can be used in a wide range of applications. Proper choice of the target material and shape, and assembly techniques enables large working air gaps and high switchpoint accuracy over the device operating temperature range. Sensor Operation The A1425 sensor IC contains two integrated Hall transducers that are used to differentially sense a magnetic field across the surface of the IC. Referring to figure 1, the trigger switches the output off (output high) when the differential magnetic field crosses zero while increasing in strength (referred to as the positive direction), and switches the output on (output low) when the differential magnetic field crosses zero while decreasing (the negative direction). The operation is achieved through the use of two separate comparators. Both comparators use the same reference point, 0 G, to provide high accuracy, but one comparator has a positive hysteresis, BHYS1, and the other a negative hysteresis, BHYS2. Therefore, one comparator switches (BOP) at the zero crossing on an increasing differential signal and the other switches (BRP) at the zero crossing on a decreasing differential signal. The hysteresis on each comparator precludes false switching on noise or target jitter. Start-up During power-on time, tPO, the output signal, VOUT, is high. Beyond this time, if the applied magnetic field, Bdiff, is absent or less than 50 G peak-to-peak, the switching state and VOUT polarity are indeterminate. VOUT will be valid for Bdiff > 50 Gp-p, after the additional settling time, tSettle, has also elapsed. Also during tPO, a circuit in the A1425 is briefly enabled that charges the on-chip capacitor. This feature reduces tPO, relative to the long RC time constant of a high-pass filter. Delay The on-chip band-pass filter induces delay in the output signal, VOUT, relative to the applied magnetic field, Bdiff. Simulation data shown in the Characteristic Data section quantify the effect of the input signal amplitude on the phase shift of the output. AC-Coupled Operation Steady-state magnet and system offsets are eliminated using an on-chip differential band-pass filter. The low and high frequency poles of this band-pass filter are set using internal integrated capacitors and resistors. The differential structure of this filter improves the ability of the IC to reject single-ended noise on the ground (GND pin) or supply line (VCC pin) and, as a result, makes it more resistant to electromagnetic interference typically seen in hostile remote-sensing environments.
11.0
Applied Magnetic Field, Bdiff
BOP(typ)
0.0
BHYS1 A
BOP(max) / BRP(max)
-11.0
A
BRP(typ) BHYS2
BOP(min) / BRP(min)
Comparator 1
Comparator 2
Switching State
Off
On
Off
Output Signal, VOUT
t+
Figure 1. Typical output characteristics with dual comparator operation. Characteristics shown without delay, see characteristic data charts for delay and phase shift contributions.
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
10
A1425-DS
A1425
High Accuracy Analog Speed Sensor with Integrated Filter Capacitor and Dual Zero-Crossing Output Signal
Applications Information
Target Selection The zero-crossing switchpoints and ac-coupled operation of this device make target selection important. For high-density target geometries or small target features that produce a sinusoidal magnetic signal, the high-pass filter is capable of filtering offsets that may be induced in the final sensor output. If such offset is present, and the target has larger features, then the high-pass filter may not be effective at higher speeds and an accuracy shift may occur. These relationships are shown in figure 2. Power Supply Protection The A1425 contains an on-chip voltage regulator and can operate over a wide supply voltage range. In applications that operate the device from an unregulated power supply, transient protection must be added externally. For applications using a regulated line, EMI/RFI protection may still be required. The circuit shown in figure 3 is the most basic configuration required for proper device operation.
Large Feature (Tooth) Differential Magnetic Flux Density, Bdiff +B
Valley
(a)
0 -B +V
VCC 1 0.1 uF RPU 4 2 VOUT
Device Output Voltage, VOUT
0
t
A1425
Differential Magnetic Flux Density, Bdiff
+B 0
Output Edge Shift
3 (Required)
(b)
Figure 3. Basic application circuit. A pull-up resistor, RPU, is
required with the output driver.
-B +V
Device Output Voltage, VOUT
0
t
Figure 2. Large Feature Effects. (a) Large target feature but no sensor offset, normal edge position. (b) Large target feature with sensor offset, shifted (advanced) output edge position.
A1425-DS
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
11
A1425
High Accuracy Analog Speed Sensor with Integrated Filter Capacitor and Dual Zero-Crossing Output Signal
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, RJA, 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, RJC, is relatively small component of RJA. 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 x IIN T = PD x RJA TJ = TA + T (1) (2) (3)
A worst-case estimate, PD(max), represents the maximum allowable power level (VCC(max), ICC(max)), without exceeding TJ(max), at a selected RJA and TA. Example Reliability for VCC at TA = 150C, using minimum-K PCB Observe the worst-case ratings for the device, specifically: RJA = 177C/W, TJ(max) = 165C, VCC(max) = 26.5 V, and ICC(max) = 7.0 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 / RJA = 15C / 177 C/W = 84 mW Finally, invert equation 1 with respect to voltage: VCC(est) = PD(max) / ICC(max) = 84 mW / 7.0 mA = 12 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 RJA. If VCC(est) VCC(max), then operation between VCC(est) and VCC(max) is reliable under these conditions. For example, when a standard diode with a 0.7 V drop is used: VS(max) = 12 V + 0.7 V = 12.7 V
For example, given common conditions such as: TA= 25C, VCC = 5.0 V, ICC = 4.2 mA, and RJA = 177 C/W, then: PD = VCC x ICC = 5.0 V x 4.2 mA = 21.0 mW T = PD x RJA = 21.0 mW x 177 C/W = 3.7C TJ = TA + T = 25C + 3.7C = 28.7C
A1425-DS
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
12
A1425
High Accuracy Analog Speed Sensor with Integrated Filter Capacitor and Dual Zero-Crossing Output Signal
Package K, 4-pin SIP
.208 5.28 .203 5.16
.0866 2.20 NOM .0592 1.50 NOM .0507 1.29 NOM E1 .045 1.14 MIN .085 2.16 MAX
C
.063 1.60 .059 1.50
B
.138 3.51 .133 3.38
E2 A .033 0.84 NOM
.021 0.53 MAX
.600 15.24 .560 14.23
.017 0.44 .014 0.35
1
2
3
4
.019 .014
0.48 0.36
.050 1.27 NOM
Dimensions in inches Millimeters in brackets, for reference only Case dimensions exclusive of mold flash or gate burrs Mold flash .010 [0.25] MAX, gate burr .008 [0.20] MAX, dambar protrusion .004 [0.10] MAX Exact case and lead configuration at supplier discretion within limits shown A Dambar removal protrusion (8X)
B Ejector mark on opposite side C
Active Area Depth .0165 [0.42] NOM
The products described herein are manufactured under one or more of the following U.S. patents: 5,045,920; 5,264,783; 5,442,283; 5,389,889; 5,581,179; 5,517,112; 5,619,137; 5,621,319; 5,650,719; 5,686,894; 5,694,038; 5,729,130; 5,917,320; and other patents pending. Allegro MicroSystems, Inc. reserves the right to make, from time to time, such departures from the detail specifications as may be required to permit improvements in the performance, reliability, or manufacturability of its products. Before placing an order, the user is cautioned to verify that the information being relied upon is current. Allegro products are not authorized for use as critical components in life-support devices or systems without express written approval. The information included herein is believed to be accurate and reliable. However, Allegro MicroSystems, Inc. assumes no responsibility for its use; nor for any infringement of patents or other rights of third parties which may result from its use. Copyright (c) 2005 Allegro MicroSystems, Inc.
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
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A1425-DS

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