A3245 Chopper-Stabilized Omnipolar Hall-Effect Switches Discontinued Product This device is no longer in production. The device should not be purchased for new design applications. Samples are no longer available. Date of status change: October 31, 2011 Recommended Substitutions: For existing customer transition, and for new customers or new applications, refer to the A1126. NOTE: For detailed information on purchasing options, contact your local Allegro field applications engineer or sales representative. Allegro MicroSystems, Inc. reserves the right to make, from time to time, revisions to the anticipated product life cycle plan for a product to accommodate changes in production capabilities, alternative product availabilities, or market demand. The information included herein is believed to be accurate and reliable. However, Allegro MicroSystems, Inc. assumes no responsibility for its use; nor for any infringements of patents or other rights of third parties which may result from its use. A3245 Chopper-Stabilized Omnipolar Hall-Effect Switches Features and Benefits Description ▪ 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) The A3245 integrated circuit is an omnipolar, ultrasensitive Hall-effect switch with a digital output. This device 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 +150°C. Superior high-temperature performance is made possible through an Allegro® 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, small-signal amplifier, chopper stabilization, Schmitt trigger, and a short circuit protected open-drain output. Advanced BiCMOS wafer fabrication processing is used to take advantage of low-voltage requirements, component matching, very low input-offset errors, and small component geometries. Packages: 3 pin SOT23W (suffix LH) 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 Continued on the next page… Not to scale Functional Block Diagram VCC Regulator Amp Low-Pass Filter Amp Sample and Hold Dynamic Offset Cancellation To All Subcircuits VOUT Control Current Limit <1Ω GND A3245-DS, Rev. 12 A3245 Chopper-Stabilized Omnipolar Hall Effect Switches Description (continued) patented 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 –40°C and 85°C for the E temperature range, and –40°C to 150°C for the L temperature range. The small geometries of the BiCMOS process allow these devices to be provided in ultrasmall packages. Package LH is an SOT23W, a miniature low-profile surfacemount package. It is lead (Pb) free, with 100% matte tin plated leadframe. Selection Guide Part Number Packing* Mounting Ambient, TA (°C) A3245ELHLT-T 7-in. reel, 3000 pieces/reel 3-pin SOT23W surface mount –40 to 85 A3245LLHLT-T 7-in. reel, 3000 pieces/reel 3-pin SOT23W surface mount –40 to 150 *Contact Allegro for additional packing options. Absolute Maximum Ratings Rating Units Supply Voltage Characteristic VCC 28 V Reverse-Supply Voltage VRCC –18 V Reverse-Supply Current IRCC –2 mA VOUT 28 V IOUTSINK Internally Limited – Output Off Voltage Output Current Magnetic Flux Density Symbol Notes B Unlimited G Range E –40 to 85 ºC Range L –40 to 150 ºC Operating Ambient Temperature TA Maximum Junction Temperature TJ(max) 165 ºC Tstg –65 to 170 ºC Storage Temperature Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 2 A3245 Chopper-Stabilized Omnipolar Hall Effect Switches OPERATING CHARACTERISTICS valid over full operating voltage and ambient temperature ranges, unless otherwise noted Characteristic Symbol Test Conditions Min. Typ. Max. Units Electrical Characteristics Supply Voltage1 Output Leakage Current VCC Operating, TJ < 165°C 3.6 – 24 V IOUTOFF VOUT = 24 V, B < BRP – – 10 μA VOUT(SAT) IOUT = 20 mA, B > BOP – – 500 mV Output Current Limit IOM B > BOP 30 – 60 mA Power-On Time tPO VCC > VCC(MIN) – – 50 μs – 200 – kHz Output On Voltage Chopping Frequency fc Output Rise Time2 tr RLOAD = 820 Ω, CS = 20 pF – – 1 μs Output Fall Time2 tf RLOAD = 820 Ω, CS = 20 pF – – 1 μs ICCON B > BOP – 1.5 3.5 mA ICCOFF B < BRP – 1.5 3.5 mA VRCC = –18 V – – –2 mA VZSupply ICC = 6.5 mA; TA = 25°C 28 – – V IZSupply VS = 28 V – – 6.5 mA BOPS South pole adjacent to branded face of device 15 38 55 G BOPN North pole adjacent to branded face of device –55 –38 –15 G BRPS South pole adjacent to branded face of device 5 20 50 G BRPN North pole adjacent to branded face of device –50 –20 –5 G BHYS |BOPX – BRPX| 5 18 30 G Supply Current Reverse Battery Current Supply Zener Clamp Voltage Supply Zener Current3 IRCC Magnetic Characteristics4 Operate Point Release Point Hysteresis 1 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). 2 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 3 A3245 Chopper-Stabilized Omnipolar Hall Effect Switches Electrical Characteristic Data Supply Current (On) versus Ambient Temperature Supply Current (On) versus Supply Voltage 5.0 5.0 4.0 VCC (V) 3.0 24 3.6 2.0 ICCON (mA) ICCON (mA) 4.0 1.0 3.0 –40 25 150 2.0 1.0 0 –50 TA (°C) 0 0 50 TA (°C) 100 150 0 25 4.0 VCC (V) 3.0 24 3.6 2.0 ICCOFF (mA) ICCOFF (mA) 20 5.0 4.0 TA (°C) –40 25 150 3.0 2.0 1.0 1.0 0 0 0 50 TA (°C) 100 0 150 5 10 15 20 25 VCC (V) Output Voltage (On) versus Ambient Temperature Output Voltage (On) versus Supply Voltage 500 500 450 450 400 400 350 350 300 VCC (V) 250 24 3.6 200 150 VOUT(SAT) (mV) VOUT(SAT) (mV) 15 Supply Current (Off) versus Supply Voltage 5.0 TA (°C) 300 –40 25 150 250 200 150 100 100 50 50 0 –50 10 VCC (V) Supply Current (Off) versus Ambient Temperature –50 5 0 0 50 TA (°C) 100 150 0 5 10 15 20 25 VCC (V) Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 4 A3245 Chopper-Stabilized Omnipolar Hall Effect Switches Magnetic Characteristic Data Operate Point (South) versus Ambient Temperature 55 -15 50 -20 45 -25 40 -30 VCC (V) 35 BOPN (G) BOPS (G) Operate Point (North) versus Ambient Temperature 24 3.6 30 -45 20 -50 –50 -55 0 50 TA (°C) 100 –50 150 Release Point (South) versus Ambient Temperature 0 50 TA (°C) 100 150 Release Point (North) versus Ambient Temperature 50 -5 45 -10 40 -15 -20 30 VCC (V) 25 24 3.6 20 BRPN (G) 35 BRPS (G) 24 3.6 -40 25 15 VCC (V) -35 -25 VCC (V) -30 24 3.6 -35 15 -40 10 -45 5 -50 –50 0 50 TA (°C) 100 150 –50 0 50 TA (°C) 100 150 Hysteresis versus Ambient Temperature 30 BHYS (G) 25 20 VCC (V) 15 24 3.6 10 5 –50 0 50 100 150 TA (°C) Continued on the next page... Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 5 A3245 Chopper-Stabilized Omnipolar Hall Effect Switches Magnetic Characteristic Data (Continued) Operate Point (South) versus Supply Voltage Operate Point (North) versus Supply Voltage 55 -15 50 -20 -25 40 TA (°C) 35 –40 25 150 30 BOPN (G) BOPS (G) 45 TA (°C) -35 –40 25 150 -40 25 -45 20 -50 15 0 5 10 15 20 -55 25 0 5 10 15 20 25 VCC (V) VCC (V) Release Point (South) versus Supply Voltage Release Point (North) versus Supply Voltage 50 -5 45 -10 40 -15 35 -20 –40 25 150 25 20 BRPN (G) TA (°C) 30 –40 25 150 -30 -35 -40 10 -45 5 TA (°C) -25 15 -50 0 5 10 15 20 25 0 5 10 VCC (V) 15 20 25 VCC (V) Hysteresis versus Supply Voltage 30 25 BHYS (G) BRPS (G) -30 TA (°C) 20 –40 25 150 15 10 5 0 5 10 15 20 25 VCC (V) Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 6 A3245 Chopper-Stabilized Omnipolar Hall Effect Switches THERMAL CHARACTERISTICS may require derating at maximum conditions, see application information Characteristic Symbol RθJA Package Thermal Resistance 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 Value Units 110 ºC/W 228 ºC/W Maximum Allowable V CC (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 V CC(max) 1-layer PCB (R θJA = 110 °C/W) 2-layer PCB (R θJA= 228 °C/W) V CC(min) 20 40 60 80 100 120 140 160 180 Temperature (°C) Power Dissipation, PD (m W) 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 1l (R aye rP QJ C A = 11 B 0º C/ 2-la y (R er PCB QJA = 228 ºC 20 40 60 W ) /W) 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 7 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 element 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 element) between the 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 0.1μF 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 devices 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) (A) VS V+ Switch to High VOUT Switch to Low Switch to Low Switch to High VS VCC CBYP 0.1 µF A3245 RLOAD VOUT Output VOUT(SAT) 0 BRPS BRPN BHYS 0 BOPS BOPN B– B+ GND BHYS 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 8 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 element. 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 highfrequency 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 device families with lower sensitivity to jitter. For more information on those devices, contact your Allegro sales representative. Regulator Hall Element Amp Low-Pass Filter Clock/Logic Sample and Hold A3245 Figure 2. Chopper Stabilization Circuit (Dynamic Quadrature Offset Cancellation) Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 9 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 × IIN (1) T = PD × RJA (2) TJ = TA + ΔT Example: Reliability for VCC at TA = 150°C, package LH, using a low-K PCB. Observe the worst-case ratings for the device, specifically: RJA = 228 °C/W, TJ(max) = 165°C, 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 = 15°C ÷ 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. (3) For example, given common conditions such as: TA= 25°C, VCC = 12 V, ICC = 1.5 mA, and RJA = 165 °C/W, then: PD = VCC × ICC = 12 V × 1.5 mA = 18 mW T = PD × RJA = 18 mW × 165 °C/W = 3°C TJ = TA + T = 25°C + 3°C = 28°C 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 10 A3245 Chopper-Stabilized Omnipolar Hall Effect Switches Package LH, 3-Pin (SOT-23W) +0.12 2.98 –0.08 1.49 D 4°±4° 3 A +0.020 0.180–0.053 0.96 D +0.10 2.90 –0.20 +0.19 1.91 –0.06 2.40 0.70 D 0.25 MIN 1.00 2 1 0.55 REF 0.25 BSC 0.95 Seating Plane Gauge Plane B PCB Layout Reference View Branded Face 8X 10° REF 1.00 ±0.13 NNT +0.10 0.05 –0.05 0.95 BSC 1 C 0.40 ±0.10 N = Last two digits of device part number T = Temperature code For Reference Only; not for tooling use (reference dwg. 802840) 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 Active Area Depth, 0.28 mm REF B Reference land pattern layout All pads a minimum of 0.20 mm from all adjacent pads; adjust as necessary to meet application process requirements and PCB layout tolerances C Branding scale and appearance at supplier discretion D Hall element, not to scale Standard Branding Reference View Package LH 3 1 2 Terminal List Name VCC Description Number Connects power supply to chip 1 VOUT Output from circuit 2 GND Ground 3 Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 11 A3245 Chopper-Stabilized Omnipolar Hall Effect Switches Copyright ©2005-2010, Allegro MicroSystems, Inc. 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, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 12