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A3245
Chopper-Stabilized Omnipolar Hall-Effect Switches
Features and Benefits
Omnipolar operation Chopper stabilization Superior temperature stability Extremely low switchpoint drift Insensitive to physical stress Reverse battery protection Output short circuit protection Solid state reliability Small size Robust EMC capability High ESD ratings (HBM)
Description
The A3245 integrated circuit is an omnipolar, ultrasensitive Hall-effect switch with a digital output. This sensor has an integrated regulator permitting operation to 24 V, making it the first omnipolar switch available for operation to 24 V. This device is especially suited for operation over extended temperature ranges, up to +150C. Superior high-temperature performance is made possible through an Allegro(R) patented dynamic offset cancellation, which reduces the residual offset voltage normally caused by device overmolding, temperature excursions, and thermal stress. The A3245 Hall-effect switch includes the following on a single silicon chip: voltage regulator, Hall-voltage generator, smallsignal amplifier, chopper stabilization, Schmitt trigger, and a short circuit protected open-drain output. Advanced BiCMOS wafer fabrication processing is used to take advantage of lowvoltage requirements, component matching, very low inputoffset errors, and small component geometries. The omnipolar operation of the A3245 allows activation with either a north or a south polarity field of sufficient strength. In the absence of a magnetic field, the output is off. This patented
Packages: 3 pin SOT23W (suffix LH), and 3 pin SIP (suffix UA)
Continued on the next page... Not to scale
Functional Block Diagram
VCC
Regulator
To All Subcircuits Sample and Hold Dynamic Offset Cancellation Low-Pass Filter
VOUT
Amp
Amp
Control
Current Limit <1
GND
A3245-DS, Rev. 2
A3245
Chopper-Stabilized Omnipolar Hall Effect Switches
process allow these devices to be provided in ultrasmall packages. The package styles available provide magnetically optimized solutions for most applications. Package LH is an SOT23W, a miniature low-profile surface-mount package, while package UA is a three-lead ultramini SIP for through-hole mounting. Each package is available in a lead (Pb) free version, with 100% matte tin plated leadframes.
Description (continued) magnetic-polarity-independence feature makes this device an excellent replacement for reed switches, with improved ease of manufacturing, because the A3245 does not require manufacturers to orient their magnets. These devices allow simple on/off switching in industrial, consumer, and automotive applications. The A3245 is rated for operation between the ambient temperatures -40C and 85C for the E temperature range, and -40C to 150C for the L temperature range. The small geometries of the BiCMOS
Selection Guide Part Number A3245ELHLT-T A3245EUA-T A3245LLHLT-T A3245LUA-T
1Pb-based
Pb-Free1 Yes Yes Yes Yes
Packing2 7-in. reel, 3000 pieces/reel Bulk, 500 pieces/bag 7-in. reel, 3000 pieces/reel Bulk, 500 pieces/bag
Mounting 3-pin SOT23W surface mount 3-pin SIP through hole 3-pin SOT23W surface mount 3-pin SIP through hole
Ambient, TA (C) -40 to 85 -40 to 150
variants are being phased out of the product line. Certain variants cited in this footnote 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. These variants include: A3245ELHLT, A3245EUA, A3245LLHT, and A3245LUA. for additional packing options.
2Contact Allegro
Absolute Maximum Ratings
Characteristic Supply Voltage Reverse-Supply Voltage Reverse-Supply Current Output Off Voltage Output Current Magnetic Flux Density Operating Ambient Temperature Maximum Junction Temperature Storage Temperature Symbol VCC VRCC IRCC VOUT IOUTSINK B TA TJ(max) Tstg Range E Range L Notes Rating 28 -18 -2 28 Internally Limited Unlimited -40 to 85 -40 to 150 165 -65 to 170 Units V V mA V - G C C C C
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
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A3245
Chopper-Stabilized Omnipolar Hall Effect Switches
OPERATING CHARACTERISTICS valid over full operating voltage and ambient temperature ranges, unless otherwise noted Characteristic Electrical Characteristics Supply Voltage1 Output Leakage Current Output On Voltage Output Current Limit Power-On Time Chopping Frequency Output Rise Time2 Output Fall Time2 Supply Current Reverse Battery Current Supply Zener Clamp Voltage Supply Zener Current3 Magnetic Characteristics4 Operate Point Release Point Hysteresis
1 2
Symbol VCC IOUTOFF VOUT(SAT) IOM tPO fc tr tf ICCON ICCOFF IRCC VZSupply IZSupply BOPS BOPN BRPS BRPN BHYS
Test Conditions Operating, TJ < 165C VOUT = 24 V, B < BRP IOUT = 20 mA, B > BOP B > BOP VCC > VCC(MIN) RLOAD = 820 , CS = 20 pF RLOAD = 820 , CS = 20 pF B > BOP B < BRP VRCC = -18 V ICC = 6.5 mA; TA = 25C VS = 28 V South pole adjacent to branded face of device North pole adjacent to branded face of device South pole adjacent to branded face of device North pole adjacent to branded face of device |BOPX - BRPX|
Min. 3.6 - - 30 - - - - - - - 28 - 15 -55 5 -50 5
Typ. - - - - - 200 - - 1.5 1.5 - - - 38 -38 20 -20 18
Max. 24 10 500 60 50 - 1 1 3.5 3.5 -2 - 6.5 55 -15 50 -5 30
Units V A mV mA s kHz s s mA mA mA V mA G G G G G
Maximum voltage must be adjusted for power dissipation and junction temperature, see Power Derating section. CS = oscilloscope probe capacitance. 3 Maximum current limit is equal to the maximum I CC(MAX) + 3 mA. 4 Magnetic flux density, B, is indicated as a negative value for north-polarity magnetic fields, and as a positive value for south-polarity magnetic fields. This so-called algebraic convention supports arithmetic comparison of north and south polarity values, where the relative strength of the field is indicated by the absolute value of B, and the sign indicates the polarity of the field (for example, a -100 G field and a 100 G field have equivalent strength, but opposite polarity).
DEVICE QUALIFICATION PROGRAM Contact Allegro for information. EMC (Electromagnetic Compatibility) REQUIREMENTS Contact Allegro for information.
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
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A3245
Chopper-Stabilized Omnipolar Hall Effect Switches
Electrical Characteristic Data
Supply Current (On) versus Ambient Temperature
5.0 4.0 5.0 4.0
Supply Current (On) versus Supply Voltage
ICCON (mA)
3.0 2.0 1.0 0 -50 0 50 TA (C) 100 150
ICCON (mA)
VCC (V) 24 3.6
TA (C) -40 25 150
3.0 2.0 1.0 0 0 5 10 VCC (V) 15 20 25
Supply Current (Off) versus Ambient Temperature
Supply Current (Off) versus Supply Voltage
5.0 4.0
5.0 4.0
ICCOFF (mA)
ICCOFF (mA)
VCC (V) 3.0 2.0 1.0 0 -50 0 50 TA (C) 100 150 24 3.6
TA (C) -40 25 150
3.0 2.0 1.0 0 0 5 10 VCC (V) 15 20 25
Output Voltage (On) versus Ambient Temperature
500 450 400 350 500 450 400 350
Output Voltage (On) versus Supply Voltage
VOUT(SAT) (mV)
VOUT(SAT) (mV)
300 250 200 150 100 50 0 -50 0 50 TA (C) 100 150
VCC (V) 24 3.6
300 250 200 150 100 50 0 0 5 10 VCC (V) 15 20 25
TA (C) -40 25 150
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
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A3245
Chopper-Stabilized Omnipolar Hall Effect Switches
Magnetic Characteristic Data
Operate Point (South) versus Ambient Temperature
55 50 45 40
BOPS (G)
VCC (V) 24 3.6
Operate Point (North) versus Ambient Temperature
-15 -20 -25 -30
BOPN (G)
VCC (V) 24 3.6
35 30 25 20 15
-50 0 50 TA (C) 100 150
-35 -40 -45 -50 -55
-50 0 50 TA (C) 100 150
Release Point (South) versus Ambient Temperature
50 45 40 35
24 3.6 VCC (V)
Release Point (North) versus Ambient Temperature
-5 -10 -15 -20
BRPN (G)
VCC (V) 24 3.6
BRPS (G)
30 25 20 15 10 5
-50 0 50 TA (C) 100 150
-25 -30 -35 -40 -45 -50
-50 0 50 TA (C) 100 150
Hysteresis versus Ambient Temperature
30 25 20 15 10 5
-50 0 50 TA (C) 100 150 VCC (V) 24 3.6
Continued on the next page...
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
BHYS (G)
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A3245
Chopper-Stabilized Omnipolar Hall Effect Switches
Magnetic Characteristic Data (Continued)
Operate Point (South) versus Supply Voltage
55 50 45 40
BOPS (G)
TA (C)
Operate Point (North) versus Supply Voltage
-15 -20 -25 -30
BOPN (G)
TA (C) -40 25 150
35 30 25 20 15
0 5 10 VCC (V) 15 20 25
-40 25 150
-35 -40 -45 -50 -55
0 5 10 VCC (V) 15 20 25
Release Point (South) versus Supply Voltage
50 45 40 35
BRPS (G)
TA (C)
Release Point (North) versus Supply Voltage
-5 -10 -15 -20
BRPN (G)
TA (C) -40 25 150
30 25 20 15 10 5
0 5 10 VCC (V) 15 20 25
-40 25 150
-25 -30 -35 -40 -45 -50
0 5 10 VCC (V) 15 20 25
Hysteresis versus Supply Voltage
30 25 20 15 10 5
0 5 10 VCC (V) 15 20 25 TA (C) -40 25 150
BHYS (G)
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
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A3245
Chopper-Stabilized Omnipolar Hall Effect Switches
THERMAL CHARACTERISTICS may require derating at maximum conditions, see application information
Characteristic Symbol Test Conditions Package LH-3, 1-layer PCB with copper limited to solder pads Package LH-3, 2-layer PCB with 0.926 in2 on each side, connected by thermal vias Package UA, 1-layer PCB with copper limited to solder pads Value 110 228 165 Units C/W C/W C/W
Package Thermal Resistance
RJA
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 20 V CC(max)
Maximum Allowable V CC (V)
1-layer PCB, Package LH (R JA= 110 C/W) 1-layer PCB, Package UA (R JA= 165 C/W) 2-layer PCB, Package LH (R JA= 228 C/W) V CC(min) 40 60 80 100 120 140 160 180 Temperature (C)
Power Dissipation versus Ambient Temperature
1900 1800 1700 1600 1500 1400 1300 1200 1100 1000 900 800 700 600 500 400 300 200 100 0 20
Power Dissipation, PD (m W)
1l (R aye rP J C A= 11 B, P 0 ac 1-la C/ ka W (R yer P ) ge L CB JA = H 165 , Pac kag C/ eU W) A
2-la y (R er PCB , JA = 228 Packa C/W ge L H )
40
60
80 100 120 Temperature (C)
140
160
180
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
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A3245
Chopper-Stabilized Omnipolar Hall Effect Switches
Functional Description
Operation The output of this device switches low (turns on) when a magnetic field perpendicular to the Hall sensor exceeds the operate point, BOPS (or is less than BOPN). After turn-on, the output voltage is VOUT(SAT). The output transistor is capable of sinking current up to the short circuit current limit, IOM, which is a minimum of 30 mA. When the magnetic field is reduced below the release point, BRPS (or increased above BRPN), the device output switches high (turns off). The difference in the magnetic operate and release points is the hysteresis, BHYS , of the device. This built-in hysteresis allows clean switching of the output even in the presence of external mechanical vibration and electrical noise. Powering-on the device in a hysteresis region, between BOPX and BRPX, allows an indeterminate output state. The correct state is attained after the first excursion beyond BOPX or BRPX. Applications It is strongly recommended that an external bypass capacitor be connected (in close proximity to the Hall sensor) between the (A)
V+ VS Switch to High Switch to High Switch to Low Switch to Low
supply and ground of the device to reduce both external noise and noise generated by the chopper stabilization technique. As is shown in Panel B of figure 1, a 0.1F capacitor is typical. Omnipolar switches allow operation with either a north pole or south pole magnet orientation, enhancing product manufacturability with the device. Extensive applications information on magnets and Hall-effect sensors is available in: * Hall-Effect IC Applications Guide, AN27701, * Hall-Effect Devices: Gluing, Potting, Encapsulating, Lead Welding and Lead Forming, AN27703.1 * Soldering Methods for Allegro's Products - SMT and ThroughHole, AN26009 All are provided in Allegro Electronic Data Book, AMS-702 and the Allegro Web site: www.allegromicro.com (B)
VS
VCC
CBYP 0.1 F
VOUT
RLOAD Sensor Output
A3245
VOUT
VOUT(SAT) 0 BRPN BRPS B- 0 BOPN BHYS BOPS BHYS B+
GND
Figure 1: Switching Behavior of Omnipolar Switches. In Panel A, on the horizontal axis, the B+ direction indicates increasing south polarity magnetic field strength, and the B- direction indicates decreasing south polarity field strength (including the case of increasing north polarity). This behavior can be exhibited when using a circuit such as that shown in panel B.
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
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A3245
Chopper-Stabilized Omnipolar Hall Effect Switches
Chopper Stabilization Technique When using Hall-effect technology, a limiting factor for switchpoint accuracy is the small signal voltage developed across the Hall element. This voltage is disproportionally small relative to the offset that can be produced at the output of the Hall sensor. This makes it difficult to process the signal while maintaining an accurate, reliable output over the specified operating temperature and voltage ranges. Chopper stabilization is a unique approach used to minimize Hall offset on the chip. The patented Allegro technique, namely Dynamic Quadrature Offset Cancellation, removes key sources of the output drift induced by thermal and mechanical stresses. This offset reduction technique is based on a signal modulationdemodulation process. The undesired offset signal is separated from the magnetic-field-induced signal in the frequency domain, through modulation. The subsequent demodulation acts as a modulation process for the offset, causing the magnetic-fieldinduced signal to recover its original spectrum at baseband, while the dc offset becomes a high-frequency signal. The magnetic-field-induced signal then can pass through a low-pass filter, while the modulated dc offset is suppressed. This configuration is illustrated in figure 2.
The chopper stabilization technique uses a 200 kHz high-frequency clock. For demodulation process, a sample and hold technique is used, where the sampling is performed at twice the chopper frequency (400 kHz). This high-frequency operation allows a greater sampling rate, which results in higher accuracy and faster signal-processing capability. This approach desensitizes the chip to the effects of thermal and mechanical stresses, and produces devices that have extremely stable quiescent Hall output voltages and precise recoverability after temperature cycling. This technique is made possible through the use of a BiCMOS process, which allows the use of low-offset, low-noise amplifiers in combination with high-density logic integration and sample-and-hold circuits. The repeatability of magnetic-field-induced switching is affected slightly by a chopper technique. However, the Allegro highfrequency chopping approach minimizes the affect of jitter and makes it imperceptible in most applications. Applications that are more likely to be sensitive to such degradation are those requiring precise sensing of alternating magnetic fields; for example, speed sensing of ring-magnet targets. For such applications, Allegro recommends its digital sensor families with lower sensitivity to jitter. For more information on those devices, contact your Allegro sales representative.
Regulator
Clock/Logic Hall Element Amp
Sample and Hold
Figure 2. Chopper Stabilization Circuit (Dynamic Quadrature Offset Cancellation)
Low-Pass Filter
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
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A3245
Chopper-Stabilized Omnipolar Hall Effect Switches
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)
Example: Reliability for VCC at TA = 150C, package LH, using a low-K PCB. Observe the worst-case ratings for the device, specifically: RJA = 228 C/W, TJ(max) = 165C, VCC(max) = 24 V, and ICC(max) = 5 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 / 228 C/W = 65.8 mW Finally, invert equation 1 with respect to voltage: VCC(est) = PD(max) / ICC(max) = 65.8 mW / 5 mA = 13.2 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, given common conditions such as: TA= 25C, VCC = 12 V, ICC = 1.5 mA, and RJA = 165 C/W, then: PD = VCC x ICC = 12 V x 1.5 mA = 18 mW T = PD x RJA = 18 mW x 165 C/W = 3C TJ = TA + T = 25C + 3C = 28C 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.
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
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A3245
Chopper-Stabilized Omnipolar Hall Effect Switches
Package LH, 3-Pin (SOT-23W)
3.00 .118 2.70 .106 0.15 [.006] M C A B 3.04 .120 2.80 .110
A
A 1.49 .059 NOM 8 0 0.20 .008 0.08 .003
3
B
B
2.10 .083 1.85 .073 Preliminary dimensions, for reference only Dimensions in millimeters U.S. Customary dimensions (in.) in brackets, for reference only (reference JEDEC TO-236 AB, except case width and terminal tip-to-tip) Dimensions exclusive of mold flash, gate burrs, and dambar protrusions Exact case and lead configuration at supplier discretion within limits shown A Hall element (not to scale) B Active Area Depth 0.28 [.011] 3X 0.10 [.004] C 3X 0.50 .020 0.30 .012 0.20 [.008] M C A B 0.95 .037 1.90 .075
A
0.96 .038
A NOM
0.60 .024 0.25 .010
1
2 0.25 .010 SEATING PLANE 1.17 .046 0.75 .030 0.15 .006 0.00 .000 C SEATING PLANE GAUGE PLANE
Package LH
3
Package UA
1
2
1
2
3
Terminal List
Name VCC VOUT GND Description Connects power supply to chip Output from circuit Ground Number Package LH 1 2 3 Package UA 1 3 2
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
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A3245
Chopper-Stabilized Omnipolar Hall Effect Switches
Package UA, 3-Pin SIP
.164 4.17 .159 4.04
C D .0805 2.04
NOM .0565 1.44 NOM D
.062 1.57 .058 1.47
D
.122 3.10 .117 2.97
B
.085 2.16 MAX
.031 0.79 REF A
.640 16.26 .600 15.24
.017 0.44 .014 0.35
1
2
3
.019 0.48 .014 0.36 .050 1.27 NOM Dimensions in inches Metric dimensions (mm) in brackets, for reference only A Dambar removal protrusion (6X)
B Ejector mark on opposite side C Active Area Depth .0195 [0.50] NOM D Hall element (not to scale)
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, 2006 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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