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Preliminary Data Sheet Subject to Change Without Notice November 10, 2004
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 or, 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 dualcomparator scheme provides for accurate switching during zero-crossing, both when the sensed field is increasing in strength and when it is decreasing, while utilizing hysteresis to prevent false switching. The zero-crossing nature of this device provides excellent repeatability for crankshaft applications. Changes in field strength at the device face caused by a moving target are sensed by the two integrated Hall transducers, generating 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 the Schmitt trigger switchpoints, guaranteeing optimal operation to low frequencies over a wide range of air gaps and temperatures. 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. 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 (part number suffix -K).
Package K, 4-pin SIP
1
2
3
4
1. VCC 2. VOUT 3. Test pin, tie to GND 4. GND
Features and Benefits
* * * * * * * * * Senses motion of ring magnet targets Integrated filter capacitor Wide operating temperature range Operation with frequency of sensed transitions from 20 Hz to 30 kHz EMI-resistant Large working air gaps 4.0 to 26.5 V operating range Output compatible with both TTL and CMOS logic families Reverse battery protection
ABSOLUTE MAXIMUM RATINGS
Supply Voltage, VCC .......................................... 28 V Reverse-Supply Voltage, VRCC ........................ -18 V Output Current, IOUT .......................................25 mA Reverse-Output Current, IROUT.....................-50 mA Reverse-Output Voltage, VROUT ...................-50 mA Operating Temperature Ambient, TA................................ -40C to 150C Maximum Junction, TJ(max)........................165C Storage Temperature, TS .................. -65C to 170C
Use the following complete part number when ordering:
Part Number A1425LK Package 4-pin plastic SIP Ambient (C) -40 to 150
Engineering samples available on a limited basis. Contact your local sales or applications support office for additional information.
A1425-DS Rev. 0b
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
Preliminary - Subject to Change Without Notice November 10, 2004
A1425
High Accuracy Analog Speed Sensor with Integrated Filter Capacitor and Dual Zero-Crossing Output Signal
Functional Block Diagram
V+ VCC (Pin 1) Test Pin (Pin 3)
Regulator Dual Hall Elements Dual Comparators
Diagnostic Circuitry
Bandpass Filter Integrated Tracking Capacitor Hall Amp Gain Stage
VOUT (Pin 2)
0.1 uF
Logic
GND (Pin 4)
A1425-DS Rev. 0b
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
2
Preliminary - Subject to Change Without Notice November 10, 2004
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 Voltage Output Zener Current Output Zener Clamp Voltage Output Short Circuit Current Limit RESPONSE CHARACTERISTICS Power-On Time2,6 Settling Time3,6 Response Time6 Upper Corner Frequency Lower Corner Frequency OUTPUT CHARACTERISTICS Output Rise Time4 Output Fall Time MAGNETIC CHARACTERISTICS Output Off Switchpoint5,6 Output On Switchpoint5,6 Applied Magnetic Field6,7
1Equivalent to I
IRCC IZCC VZCC IZOUT VZOUT IOUT(lim)
VCC = -18 V VCC = 28 V ICC = 10 mA1, TA = 25C VOUT = 28 V IOUT = 3 mA, TA = 25C
- - 28 - 28 -
- - 33 - - -
-1 10 37 3 - 50
mA mA V mA V mA
tPO tS tR fcu fcl tr tf BOP BRP Bdiff
VCC > VCC(min) fBdiff 100 Hz Equal to tPO + tS; fBdiff 100 Hz -3 dB, single pole -3 dB, single pole RPU = 1 k, C = 10 pF RPU = 1 k, ISINK = 20 mA, C = 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
- 0 4.5 30 - - -
4.5 - - - - - -
9 50 59 - 20 200 200
ms ms ms kHz Hz ns ns
-11 -11 50
0 0 -
11 11 1250
G G G
CC(max) + 3 mA. 2Time required to initialize device. 3Time required for the output switchpoints to be within specification. 4Output Rise Time will be dominated by the RC time constant. 5For 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. 6 See Definitions of Terms section. 7 Exceeding the maximum magnetic field may result in compromised absolute accuracy.
A1425-DS Rev. 0b
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
3
Preliminary - Subject to Change Without Notice November 10, 2004
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 Minimum-K PCB (single-sided with copper limited to solder pads) Min. 177 Typ. - Max Units - C/W
30 28 26 24 22 20 18 16 14 12 10 8 6 4 2 0 20 40
Power Derating Curve TJ(max) = 165C; ICC = ICC(max)
VCC(max)
900 850 800 750 700 650 600 550 500 450 400 350 300 250 200 150 100 50 0 20
Maximum Power Dissipation, PD(max) TJ(max) = 165C; VCC = VCC(max); ICC = ICC(max)
Maximum Allowable VCC (V)
Power Dissipation, PD (m W)
M (R inim
J A
Minimum-K PCB (RJA = 177 C/W)
u = m-K 17 P 7C C B /W )
VCC(min)
60
80
100
120
140
160
180
40
60
80 100 120 Temperature (C)
140
160
180
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, tS - 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 - The total time required for generating zerocrossing output transitions after power-up (the sum of power-on time and settling time).
A1425-DS Rev. 0b
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
4
Preliminary - Subject to Change Without Notice November 10, 2004
A1425
High Accuracy Analog Speed Sensor with Integrated Filter Capacitor and Dual Zero-Crossing Output Signal
Empirical Results
10.0 9.0 8.0 7.0 6.0 5.0 4.0 3.0 2.0 1.0 0.0 -50
Over VCC Range
VCC (V)
4.5 12.0 20.0
ICC(OFF) by TA
ICC(OFF) by VCC
10.0 9.0 8.0 7.0 6.0 5.0 4.0 3.0 2.0 1.0 0.0 Over TA Range
TA (C)
150 25 -40
Current (mA)
0
50
100
150
200
Current (mA)
0
5
10
15
20
25
Ambient Temperature, TA (C)
Supply Voltage, VCC (V)
10.0 9.0 8.0 7.0 6.0 5.0 4.0 3.0 2.0 1.0 0.0 -50
Over VCC Range
VCC (V)
4.5 12.0 20.0
ICC(ON) by TA
ICC(ON) by VCC
10.0 9.0 8.0 7.0 6.0 5.0 4.0 3.0 2.0 1.0 0.0 Over TA Range
TA (C)
150 25 -40
Current (mA)
Current (mA)
0
50
100
150
200
0
5
10
15
20
25
Ambient Temperature, TA (C)
Supply Voltage, VCC (V)
500 450 400 350 300 250 200 150 100 50 0 -50
Over VCC Range; ISINK = 20 mA
VCC (V)
4.5 12.0 20.0
VOUT(SAT) by TA
0
50
100
150
200
500 450 400 350 300 250 200 150 100 50 0 0
Over TA Range; ISINK = 20 mA
TA (C)
150 25 -40
VOUT(SAT) by VCC
Voltage (mV)
Voltage (mV)
5
10
15
20
25
Ambient Temperature, TA (C)
Supply Voltage, VCC (V)
Continued on next page.
A1425-DS Rev. 0b
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
5
Preliminary - Subject to Change Without Notice November 10, 2004
A1425
High Accuracy Analog Speed Sensor with Integrated Filter Capacitor and Dual Zero-Crossing Output Signal
Empirical Results, continued
Repeatability ( of Rotation)
Air Gap (mm)
Repeatability ( of Rotation)
Air Gap (mm)
A1425-DS Rev. 0b
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
6
Preliminary - Subject to Change Without Notice November 10, 2004
A1425
High Accuracy Analog Speed Sensor with Integrated Filter Capacitor and Dual Zero-Crossing Output Signal
Simulation Results
Typical Applied Magnetic Fields, Bdiff by Frequency of Sensed Transitions Over the Range of Ambient Operating Temperatures, TA 40 35 30 25 Bdiff(min) (G) 20 -40 15 10 5 0 0.01
25
150
0.1
1 Frequency, fBdiff (kHz)
10
13
Typical Phase Shifts, by Frequency of Sensed Transitions Over the Range of Applied Magnetic Fields, Bdiff (GP-P) 40 30 20
50 100 500 10 750
Phase Shift () 0 -10 -20 -30 -40 -50 -60 0.01 13
1250
0.1 Frequency, fBdiff
1 (kHz)
10
Continued on next page.
A1425-DS Rev. 0b
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
7
Preliminary - Subject to Change Without Notice November 10, 2004
A1425
High Accuracy Analog Speed Sensor with Integrated Filter Capacitor and Dual Zero-Crossing Output Signal
Simulation Results, continued
Typical Output Signal Delay by Frequency of Sensed Transitions, >100 Hz Over the Range of Applied Magnetic Fields, Bdiff (GP-P) 20 IOUT Leading 15 10 5 0 IOUT Lagging -5 -10 -15 -20 0.1 1 Frequency, fBdiff (kHz) 10 13
IOUT Delay (s)
75 0
12
50
50 0
Typical Output Signal Delay by Frequency of Sensed Transitions, 0 to 100 Hz Over the Range of Applied Magnetic Fields, Bdiff (GP-P) IOUT Leading 1000 0 -1000 -2000 -3000 IOUT Lagging -4000
IOUT Delay (s)
50 100
1250 750
500
10
-5000 -6000 0
0
50
100 Frequency, fBdiff (Hz)
A1425-DS Rev. 0b
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
8
Preliminary - Subject to Change Without Notice November 10, 2004
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. (EMC test results are available after review of first silicon.)
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 test is done with no external components.
Vs
R2
C1
1 VCC
R1
2
4
GND
1425
VOUT
C2
Test 3
Component R1* R2 C1 C2
Value 1.2 100 0.1 0.1
Units k F F
*Pull-up resistor not required for protection but for normal operation.
Recommended EMC test circuit. Test circuit recommended configuration may change after evaluation of first silicon.
A1425-DS Rev. 0b
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
9
Preliminary - Subject to Change Without Notice November 10, 2004
A1425
High Accuracy Analog Speed Sensor with Integrated Filter Capacitor and Dual Zero-Crossing Output Signal
Applications Information
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 a 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 at the zero crossing on an increasing differential signal and the other switches 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, tS, 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.
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.
A1425-DS Rev. 0b
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
10
Preliminary - Subject to Change Without Notice November 10, 2004
A1425
High Accuracy Analog Speed Sensor with Integrated Filter Capacitor and Dual Zero-Crossing Output Signal
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. 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 2 is the most basic configuration required for proper device operation. 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)
For example, given common conditions such as: TA= 25C, VCC = 12 V, ICC = 4.2 mA, and RJA = 177 C/W, then: PD = VCC x ICC = 12 V x 4.2 mA = 50 mW T = PD x RJA = 50 mW x 177 C/W = 9C TJ = TA + T = 25C + 9C = 34C 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, package L-I1, using minimumK 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 = 91 mW
VCC 1 0.1 uF 4 2 RPU VOUT
Finally, invert equation 1 with respect to voltage: VCC(est) = PD(max) / ICC(max) = 91 mW / 7.0 mA = 13 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.
A1425
3
Figure 2. Basic application circuit. A pull-up resistor is required with
the output driver.
A1425-DS Rev. 0b
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
11
Preliminary - Subject to Change Without Notice November 10, 2004
A1425
High Accuracy Analog Speed Sensor with Integrated Filter Capacitor and Dual Zero-Crossing Output Signal
Package K, 4-pin SIP
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) 2004 Allegro MicroSystems, Inc.
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
12
A1425-DS Rev. 0b

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