A3250_06 ALLEGRO
Document overview
- Manufacturer or author: Provided By www.digicamel.com(FREE DATASHEET DOWNLOAD SITE)
- PDF pages: 15
Technical content
Description
The A3250 and A3251 are field-programmable, chopper- stabilized, unipolar Hall-effect switches designed for use in high-temperature applications. These devices use a chop- per-stabilization technique to eliminate offset inherent in single-element devices. The A3250 and A3251 are externally programmable devices. The devices have a wide range of programmabil- ity of the magnetic operate point (B OP) while the hysteresis remains fixed. This advanced feature allows for optimiza- tion of the sensor switchpoint and can drastically reduce the effects of variations found in a production environment, such as magnet and device placement tolerances. These devices provide on-chip transient protection. A Zener clamp on the power supply protects against overvoltage conditions on the supply line. These devices also include short-circuit protection on the output. The output of the A3250 switches LOW when subjected to a south-polarity magnetic field with a flux density that exceeds the threshold for B OP , and switches HIGH when the 3250-DS Rev. 3 Features and Benefits ▪ Chopper stabilization for stable switchpoints throughout operating temperature range ▪ Externally programmable operate point (through VCC pin) ▪ On-board voltage regulator for 4.2 V to 24 V operation ▪ On-chip protection against: ▫ Supply transients ▫ Output short-circuits ▫ Reverse-battery condition Field-Programmable, Chopper-Stabilized Unipolar Hall-Effect Switches Continued on the next page… 3 pin SIP (suffix UA) Functional Block Diagram Not to scale A3250 and A3251 Current LimitAmp Regulator Program/Lock Low-Pass Filter VCC GND Programming Logic Offset Adjust VOUT Dynamic Offset Cancellation Sample and Hold
Field-Programmable, Chopper-Stabilized, Unipolar Hall-Effect Switches A3250 and A3251 2Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com Selection Guide Part Number Pb-free 1 Packing2 Package TA (ºC) VOUT Power-On Running 3 A3250ELT-T Yes Bulk, 500 pieces/bag Surface mount –40 to 85 High LowA3250ELTTR-T Yes 7-in. reel, 1000 pieces/reel A3250EUA-T Yes Bulk, 500 pieces/bag SIP through hole A3250LLT-T Yes Bulk, 500 pieces/bag Surface mount –40 to 150 High LowA3250LLTTR-T Yes 7-in. reel, 1000 pieces/reel A3250LUA-T Yes Bulk, 500 pieces/bag SIP through hole A3251ELT-T Yes Bulk, 500 pieces/bag Surface mount –40 to 85 Low HighA3251ELTTR-T Yes 7-in. reel, 1000 pieces/reel A3251EUA-T Yes Bulk, 500 pieces/bag SIP through hole A3251LLT-T Yes Bulk, 500 pieces/bag Surface mount –40 to 150 Low HighA3251LLTTR-T Yes 7-in. reel, 1000 pieces/reel A3251LUA-T Yes Bulk, 500 pieces/bag SIP through hole 1Pb-based variants are being phased out of the product line. a. Certain variants cited in this footnote are in production but have been determined to be LAST TIME BUY. 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: October 31, 2006. Deadlilne for receipt of LAST TIME BUY ORDERS: April 27, 2007. These variants include: A3250ELT, A3250ELTTR, A3250EUA, A3251ELT, A3251ELTTR, A3251EUA, A3251LLT, A3251LLTTR, and A3251LUA. b. 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: A3250LLT, A3250LLTTR, A3250LUA. 2Contact Allegro for additional packing options. 3In south polarity magnetic field of sufficient strength. field drops below the magnetic release point, BRP . The output of the A3251 has the opposite polarity, switching HIGH in a south- polarity magnetic field that B OP , and switching LOW when the field drops below BRP . The other differences in the devices are the power-on state. The A3250 powers-on in the HIGH state, while the A3251 powers-on in the LOW state. Three package styles provide a magnetically optimized package for most applications. Type LT is a miniature SOT89/TO-243AA surface mount package that is thermally enhanced with an exposed ground tab, and type UA is a three-lead ultramini SIP for through-hole mounting. The packages are lead (Pb) free, with 100% matte tin plated leadframes (suffix, –T). Description (continued) Absolute Maximum Ratings Characteristic Symbol Notes Rating Units Supply Voltage V CC 26.5 V Reverse Supply Voltage V RCC –18 V Zener Overvoltage V Z 30 V Output Current I OUT 20 mA Magnetic Flux Density B Unlimited G Operating Ambient Temperature T A Range E –40 to 85 ºC Range L –40 to 150 ºC Maximum Junction Temperature T J(max) 165 ºC Storage Temperature T stg –65 to 170 ºC
Field-Programmable, Chopper-Stabilized, Unipolar Hall-Effect Switches A3250 and A3251 3Allegro MicroSystems, Inc. Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com OPERATING CHARACTERISTICS valid over operating TA and VCC, unless otherwise specified Characteristic Symbol Test Conditions Min. Typ. Max. Units
ELECTRICAL CHARACTERISTICS
1 VCC Running mode 4.2 – 24 V Output Saturation Voltage V OUT(sat) IOUT = 20 mA; Switch state = ON – 175 400 mV Output Leakage Current I OFF VOUT = 24 V; Switch state = OFF – – 10 μA Supply Current ICC(off) A3250; B < BRP; VOUT = HIGH – 4.0 7.0 mA A3251; B > BOP; VOUT = HIGH – 4.0 7.0 mA ICC(on) A3250; B > BOP; VOUT = LOW – 6.0 10.0 mA A3251; B < BRP; VOUT = LOW – 6.0 10.0 mA Output Rise Time t r RLOAD = 820 Ω, CLOAD = 10 pF – – 5.0 μs Output Fall Time t f RLOAD = 820 Ω, CLOAD = 10 pF – – 5.0 μs Chopping Frequency f C – 340 – kHz Power-Up Time t on VOUT = HIGH – 20 50 μs Output Current Limit1,2 IOUT(lim) Short-circuit protection 60 90 120 mA Power-On State POS A3250; B < BRP, t > ton – HIGH – mV A3251; B < BRP, t > ton – LOW – mV MAGNETIC CHARACTERISTICS Initial Operate Point B OP –20 13 50 G Temperature Drift of BOP ΔBOP BOP ≤ 500 gauss –35 – 35 G Hysteresis (BOP – BRP)B hys Package TA range = J 5.0 18 35 G Package TA range = L 5.0 13 35 G PROGRAMMING CHARACTERISTICS Programmable B OP Values3 BOP(prog) 50 – ≥350 G Number of Programming Bits – Switchpoint set – 6 – Bit Programming lock – 1 – Bit Resolution B RES – 7.0 – G TRANSIENT PROTECTION CHARACTERISTICS Supply Zener Voltage V Z 28 – – V Supply Zener Current I Z VCC = 28 V – – 13 mA Reverse Battery Current I RCC VRCC = –18 V, TJ < TJ(max) – – –5.0 mA 1 Do not exceed TJ(max): Additional information on power derating is provided in the applications section. 2 Short-circuit protection is not intended for continuous operation; permanent damage may result. 3 Device can be used below 50 G but is not guaranteed to be a unipolar switch. It is the responsibility of the programmer to ver ify that the desired switchpoint has been achieved.
Field-Programmable, Chopper-Stabilized, Unipolar Hall-Effect Switches A3250 and A3251 4Allegro MicroSystems, Inc. Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com Typical Characterization Data All data are taken with A3250 devices, the average of 3 lots, 30 pieces per lot Program Code: 1, VCC =1 2V -50 -20 10 40 70 100 130 160 Program Code: 1, VCC =1 2V -20 -15 -10 -50 -20 10 40 70 100 130 160 Program Code: 8, VCC =1 2V -50 -20 10 40 70 100 130 160 Program Code: 8, VCC =1 2V -50 -20 10 40 70 100 130 160 Program Code: 16, VCC =1 2V 100 105 110 115 120 125 130 -50 -20 10 40 70 100 130 160 Program Code: 16, VCC =1 2V 100 105 110 -50 -20 10 40 70 100 130 160 Average BOP vs. TA Average BOP vs. TA Average BOP vs. TA Average BRP vs. TA Average BRP vs. TA Average BRP vs. TA TA (°C)TA (°C) TA (°C) TA (°C) TA (°C)TA (°C) Average BOP (G)Average BOP (G)Average BOP (G) Average BRP (G)Average BRP (G)Average BRP (G)
Field-Programmable, Chopper-Stabilized, Unipolar Hall-Effect Switches A3250 and A3251 5Allegro MicroSystems, Inc. Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com Typical Characterization Data All data are taken with A3250 devices, the average of 3 lots, 30 pieces per lot Average Bhys vs. Temperature Program Code: 1, VCC =1 2V -50 -20 10 40 70 100 130 160 Average Bhys vs. Temperature Program Code: 16, VCC =1 2V -50 -20 10 40 70 100 130 160 Average Bhys vs. Temperature Program Code: 8, VCC =1 2V -50 -20 10 40 70 100 130 160 -40°C to 25°C and 150°C to 25°C -30 -20 -10 Code 1 Code 8 Code 16 -40°C to 25°C 150°C to 25°C Average BOP vs. Temperature TA (°C)TA (°C) TA (°C) TA (°C) Average BHYS (G)Average BHYS (G) Average BHYS (G)Average BOP (G)
Field-Programmable, Chopper-Stabilized, Unipolar Hall-Effect Switches A3250 and A3251 6Allegro MicroSystems, Inc. Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com Typical Characterization Data Average ICC(on) vs. Temperature -50 -20 10 40 70 100 130 160 ICC(on) (mA) ICC(on) @3 . 8V ICC(on) @1 2 . 0V ICC(on) @2 6 . 5V Average ICC(off) vs. Temperature -50 -20 10 40 70 100 130 160 ICC(off) (mA) ICC(off) @3 . 8V ICC(off) @1 2 . 0V ICC(off) @2 6 . 5V Average VOUT(SAT) vs. Temperature VCC = 3.8 V, Iout =2 0m A 140 160 180 200 220 240 260 280 -50 -20 10 40 70 100 130 160 VOUT(SAT) (mV) TA (°C)TA (°C) TA (°C) All data are taken with A3250 devices, the average of 3 lots, 30 pieces per lot
Field-Programmable, Chopper-Stabilized, Unipolar Hall-Effect Switches A3250 and A3251 7Allegro MicroSystems, Inc. Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com THERMAL CHARACTERISTICS may require derating at maximum conditions, see application information Characteristic Symbol Test Conditions Value Units Package Thermal Resistance RθJA Package UA, 1-layer PCB with copper limited to solder pads 165 ºC/W Package LT, 1-layer PCB with copper limited to solder pads 180 ºC/W Package LT, 2-layer PCB with 0.94 in 2 copper each side 78 ºC/W 20 40 60 80 100 120 140 160 180 TA (ºC) Maximum Allowable VCC (V) Power Derating Curve (RθJA = 165 ºC/W) 1-layer PCB, Package UA (RθJA = 180 ºC/W) 1-layer PCB, Package LT (RθJA = 78 ºC/W) 2-layer PCB, Package LT VCC(min) VCC(max) 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 20 40 60 80 100 120 140 160 180 Temperature (°C) Power Dissipation, PD (mW) Power Dissipation θJA =1 65º C/W) 1-layer PCB, Pa ckage UA θJA =1 80º C / 1-layer PCB, Pac kage LT θJA =7 8º C / W ) 2-layer PCB, Pa ckage L T BOP BRP BHYS VOUT(off) VOUT VOUT(on)(sat) Switch to Low Switch to High Hysteresis of ΔVOUT Switching Due to ΔB Hysteresis Curves A3250 BOP BRP BHYS Switch to High Switch to Low VOUT(off) VOUT VOUT(on)(sat) Hysteresis of ΔVOUT Switching Due to ΔB A3251 Output voltage in relation to sensed magnetic flux density in a south polarity magnetic field of sufficient strength. Transition through BOP must precede transition through BRP.
Field-Programmable, Chopper-Stabilized, Unipolar Hall-Effect Switches A3250 and A3251 8Allegro MicroSystems, Inc. Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com Functional Description Chopper-Stabilized Technique The Hall sensor is based on a Hall element, a small sheet of semiconductor material in which a constant bias current flows when a constant voltage source is applied. The output takes the form of a voltage measured across the width of the Hall element, and has negligible value in the absence of a magnetic field. When a magnetic field is applied with flux lines at right angles to the current in the Hall element, a small signal voltage directly proportional to the strength of the magnetic field occurs at the output of the Hall element. This small signal voltage is disproportionally small relative to the offset produced at the input of the device. This makes it very difficult to process the signal and maintain an accurate, reliable output over the specified temperature and voltage range. There- fore, it is important to reduce any distortion of the signal that could be amplified when the signal is processed. Chopper stabilization is a unique approach used to minimize input offset on the Hall IC. This technique removes a key source of output drift due to temperature and mechanical stress, and produces a 3X reduction in offset in comparison to other, conventional methods. This offset reduction chopping technique is based on a sig- nal modulation-demodulation process. The undesired offset signal is separated from the magnetically-induced signal in the frequency domain. The offset (and any low-frequency noise) component of the signal can be seen as signal distortion added after the signal modulation process has taken place. Therefore, the dc offset is not modulated and remains a low-frequency component. Consequently, the signal demodulation process acts as a modulation process for the offset, causing the magnetically- induced signal to recover its original spectrum at baseband while the dc offset becomes a high-frequency signal. Then, the signal passes using a low-pass filter, while the modulated dc offset is suppressed. The advantage of this approach is significant offset reduction, which desensitizes the Hall IC against the effects of temperature and mechanical stress. The disadvantage is that this technique features a demodulator that uses a sample-and-hold block to store and recover the signal. This sampling process can slightly degrade the SNR (signal-to-noise ratio) by producing replicas of the noise spectrum at the baseband. This degradation is a function of the ratio between the white noise spectrum and the sampling frequency. The effect of the degradation of the SNR is higher jitter, also known as signal repeatability. However, the jitter in a continuous-time device can be 5X that of the A3250/A3251. Chopper stabilization circuit (dynamic quadrature offset cancellation) Amp Regulator Sample and Hold / LPF
Figure 1. Pulse amplitudes and durations 1Programming voltages are measured at the VCC pin. the current necessary to blow the fuse. software is available free of charge. hysteresis, BHYS , is fixed. physically represented by 6 bitfields in the onboard registers. CC to fall to zero (which clears the registers). pulse is sent at the end of the pulse sequence.
10Allegro MicroSystems, Inc.
- A bitfield address sequence.
- When permanently setting the bitfield, a long V
- When permanently setting the bitfield, the level of VCC must
preparing to set additional bitfields. period, enough to blow the corresponding bitfield-level fuse. Figure 3. Pulse sequence to permanently encode calibration value 5 (101 binary, or bitfield address 3 and bitfield address 1). Figure 2. Pulse sequence to provisionally try calibration value 5.
11Allegro MicroSystems, Inc. Figure 5. Pulse sequence to select addresses Figure 6. Pulse sequence to encode lock bit setting the other bitfields, as shown in figure 6. but also to blow the bitfield fuse. Figure 4. Addressing mode enable pulse sequence
Field-Programmable, Chopper-Stabilized, Unipolar Hall-Effect Switches A3250 and A3251 12Allegro MicroSystems, Inc. Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
Application Information
For additional general application information, visit the Allegro MicroSystems Web site at www. allegromicro.com. Typical application circuit Typical Application Circuit It is strongly recommended that an external ceramic bypass capacitor, CBYP, in the range of 0.01 μF to 0.1 μF be connected between the VCC pin and the supply and GND pin to reduce both external noise and noise generated by the chopper-stabiliza- tion technique. (The diagram at the right shows C BYP at 0.1 μF.) CBYP should be installed so that the traces that connect it to the A3250/A3251 are no greater than 5 mm in length. (For program- ming the device, the capacitor may be further away from the device, including mounting on the board used for programming the device.) The series resistor R S, in combination with CBYP creates a filter for EMI pulses. (Additional information on EMC is provided on the Allegro MicroSystems Web site.) R S will have a drop of approximately 800 mV . This must be taken into consider- ation when determining the minimum VCC requirement for the A3250/A3251. The pull-up resistor, R L, should be chosen to limit the current through the output transistor; do not exceed the maximum continuous output current of the device. GND A3250/A3251 VCC VSupply 0.1 μF A RL CBYP RS 100 Ω 1.2 kΩ VOUT A A Maximum separation 5 mm from CBYP to device
Field-Programmable, Chopper-Stabilized, Unipolar Hall-Effect Switches A3250 and A3251 13Allegro MicroSystems, Inc. Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 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 sup- plied power or improving the heat dissipation properties of the application. This section presents a procedure for correlating factors affecting operating T J. (Thermal data is also available on the Allegro MicroSystems Web site.) The Package Thermal Resistance, RθJA, is a figure of merit sum- marizing 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 θJC, is relatively small component of RθJA. 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 T J, at PD. PD = VIN × IIN (1) Δ T = PD × RθJA (2) T J = TA + ΔT (3) For example, given common conditions such as: TA= 25°C, VCC = 12 V, ICC = 4 mA, and RθJA = 165 °C/W, then: P D = VCC × ICC = 12 V × 4 mA = 48 mW Δ T = PD × RθJA = 48 mW × 165 °C/W = 8°C T J = TA + ΔT = 25°C + 8°C = 33°C A worst-case estimate, PD(max), represents the maximum allow- able power level (VCC(max), ICC(max)), without exceeding TJ(max), at a selected RθJA and TA. Example: Reliability for VCC at TA = 150°C, package UA, using minimum-K PCB. Observe the worst-case ratings for the device, specifically: RθJA = 165°C/W, TJ(max) = 165°C, VCC(max) = 24 V , and ICC(max) = 10 mA. Calculate the maximum allowable power level, PD(max). First, invert equation 3: ΔTmax = 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) = ΔTmax ÷ RθJA = 15°C ÷ 165 °C/W = 91 mW Finally, invert equation 1 with respect to voltage: VCC(est) = PD(max) ÷ ICC(max) = 91 mW ÷ 10 mA = 9 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 reli- able operation between VCC(est) and VCC(max) requires enhanced RθJA. If VCC(est) ≥ VCC(max), then operation between VCC(est) and VCC(max) is reliable under these conditions.
Field-Programmable, Chopper-Stabilized, Unipolar Hall-Effect Switches A3250 and A3251 14Allegro MicroSystems, Inc. Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 4.60 4.40 .181 .173 2.60 2.29 .102 .090 4.25 3.94 .167 .155 2.24 NOM .0880 1.14 NOM .0450 1.60 1.40 .063 .055 1.20 0.89 .047 .0350.44 0.35 .017 .014 0.56 .022 .0170.44 1.83 .072 .0641.62 321 B Preliminary dimensions, for reference only Dimensions in millimeters U.S. Customary dimensions (in.) in brackets, for reference only (reference JEDEC TO-243 AA) 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; location controlling dimensions inches) B Active Area Depth 0.775 [.0305] nominal 1.50 .059 0.48 .019 .0140.362X 0.10 [.004] M C A B 2X A
Field-Programmable, Chopper-Stabilized, Unipolar Hall-Effect Switches A3250 and A3251 15Allegro MicroSystems, Inc. Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com Package UA, 3-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 de par tures from the detail spec i fi ca tions as may be required to permit improvements in the per for mance, 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 sys tems without express written approval. The in for ma tion in clud ed herein is believed to be ac cu rate and reliable. How ev er, Allegro MicroSystems, Inc. assumes no re spon si bil i ty for its use; nor for any in fringe ment of patents or other rights of third parties which may result from its use. Copyright © 2004, 2006 Allegro MicroSystems, Inc. B D D D .164 .159 4.17 4.04 .122 .117 3.10 2.97 .062 .058 1.57 1.47 .017 .014 0.44 0.35 .019 .014 0.48 0.36 .640 .600 16.26 15.24 .085 MAX 2.16 .050 NOM 1.27 .031 REF 0.79 2.06 NOM .081 1.45.057 NOM Dimensions in inches Metric dimensions (mm) in brackets, for reference only 231 A A B C C Dambar removal protrusion (6X) Active Area Depth .0195 [0.50] NOM D Hall element (not to scale) controlling dimensions inches Ejector mark on opposite side