A3250 ALLEGRO
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A3250-DS Worcester, Massachusetts 01615-0036 (508) 853-5000
115 Northeast Cutoff, Box 15036
www.allegromicro.com Allegro MicroSystems, Inc. AB SO LUTE MAX I MUM RAT INGS Operating Temperature Ambient, T On-chip protection against: y Supply transients y Output short-circuits y Reverse-battery condition Field-Programmable, Chopper-Stabilized Unipolar Hall-Effect Switches Features and Benefits The A3250 and A3251 are field-programmable, chopper-stabilized, unipolar Hall- effect switches designed for use in high-temperature applications. These devices use a chopper-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 programmability of the magnetic operate point (B OP) while the hys- teresis remains fixed. This advanced feature allows for optimization of the sensor switchpoint and can drastically reduce the effects of variations found in a produc- tion 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 mag- netic field with a flux density that exceeds the threshold for B OP , and switches HIGH when the 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. These devices are available in a TO-92 three-lead ultra-mini SIP (Single In-line Package), with either straight or formed and trimmed lead configuration. 1. VCC 2. GND 3. VOUT Package UA, 3-pin SIP 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 231 TL Option Part Number Package TA (ºC) Bhys(typ) (G) VOUT Power-On Running* A3250JUA A3250JUATL Straight lead Formed lead –40 to 115 18 High Low A3250LUA A3250LUATL Straight lead Formed lead –40 to 150 13 A3251JUA A3251JUATL Straight lead Formed lead –40 to 115 18 Low High A3251LUA A3251LUATL Straight lead Formed lead –40 to 150 13 *In south polarity magnetic field of sufficient strength. Use the following complete part numbers when ordering:
A3250-DS Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com Allegro MicroSystems, Inc. Field-Programmable, Chopper-Stabilized, Unipolar Hall-Effect Switches A3250 and A3251 Functional Block Diagram Current LimitAmp Regulator Program/Lock Low-Pass Filter VCC GND Programming Logic Offset Adjust VOUT Dynamic Offset Cancellation Sample and Hold BOP BRP BHYS VOUT(off) VOUT VOUT(on)(sat) Switch to Low Switch to High Hysteresis of∆VOUT Switching Due to∆B Hysteresis Curves A3250 BOP BRP BHYS Switch to High Switch to Low VOUT(off) VOUT VOUT(on)(sat) Hysteresis of∆VOUT Switching Due to∆B A3251 Output voltage in relation to sensed magnetic flux density in a south polarity magnetic field of sufficient strength. Transition through B OP must precede transition through BRP.
A3250-DS Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com Allegro MicroSystems, Inc. Field-Programmable, Chopper-Stabilized, Unipolar Hall-Effect Switches A3250 and A3251 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 ∆BOP 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.
A3250-DS Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com Allegro MicroSystems, Inc. Field-Programmable, Chopper-Stabilized, Unipolar Hall-Effect Switches A3250 and A3251 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)
A3250-DS Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com Allegro MicroSystems, Inc. Field-Programmable, Chopper-Stabilized, Unipolar Hall-Effect Switches A3250 and A3251 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)
A3250-DS Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com Allegro MicroSystems, Inc. Field-Programmable, Chopper-Stabilized, Unipolar Hall-Effect Switches A3250 and A3251 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
A3250-DS Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com Allegro MicroSystems, Inc. Field-Programmable, Chopper-Stabilized, Unipolar Hall-Effect Switches A3250 and A3251 THERMAL CHARACTERISTICS may require derating at maximum conditions, see application information Characteristic Symbol Test Conditions Min. Typ. Max Units Package Thermal Resistance RθJA Package UA, minimum-K PCB (single-sided with copper limited to solder pads) 165 – – ºC/W 20 40 60 80 100 120 140 160 180 Maximum Allowable VCC (V) TJ(max) = 165ºC; ICC =I CC(max) Power Derating Curve (RθJA = 165 ºC/W) Minimum-K PCB, Package UA 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) TJ(max) = 165ºC; VCC =V CC(max);I CC =I CC(max) Maximum Power Dissipation, PD(max) θJA =1 6 5 ºC/W) Minimum-K P CB,PackageU A
A3250-DS Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com Allegro MicroSystems, Inc. Field-Programmable, Chopper-Stabilized, Unipolar Hall-Effect Switches A3250 and A3251 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.
- 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. which is 110). Bit 2 is ignored, and so remains 0. 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 (101 binary, or bitfield address 3 and bitfield address 1).
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
A3250-DS Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com Allegro MicroSystems, Inc. Field-Programmable, Chopper-Stabilized, Unipolar Hall-Effect Switches A3250 and A3251
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. The series resistor RS, 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
A3250-DS Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com Allegro MicroSystems, Inc. Field-Programmable, Chopper-Stabilized, Unipolar Hall-Effect Switches A3250 and A3251 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) ∆ T = PD × RθJA (2) T J = TA + ∆T (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 ∆ T = PD × RθJA = 48 mW × 165 °C/W = 8°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: ∆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 ÷ 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.
A3250-DS Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com Allegro MicroSystems, Inc. Field-Programmable, Chopper-Stabilized, Unipolar Hall-Effect Switches A3250 and A3251 Package UA, 3-Pin; (TO-92) The products described herein are manufactured under one or more of the following U.S. patents: 5,045,920; 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 Allegro MicroSystems, Inc.
A3250-DS Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com Allegro MicroSystems, Inc. Field-Programmable, Chopper-Stabilized, Unipolar Hall-Effect Switches A3250 and A3251