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A1242
Two-Wire Chopper-Stabilized Hall Effect Latch
The A1242 Hall effect latch is a two-wire latch especially suited for operation over extended temperature ranges, from -40 to +150C. Superior high-temperature performance is made possible through the Allegro(R) patented dynamic offset cancellation technique, which reduces the residual offset voltage normally caused by device overmolding, temperature dependencies, and thermal stress. The current-switching output technique allows for the reduction in cost in the wiring harness because only two connections to the sensor are required. The current-switching output structure also inherently provides more immunity against EMC/ESD transients. These sensors have low magnetic thresholds, thereby enabling more flexibility in the magnetic circuit design. The Hall effect latch will be in the high output current state in the presence of a magnetic South Pole field of sufficient magnitude and will remain in this state until a sufficient North Pole field is present. The A1242 includes the following on a single silicon chip: a voltage regulator, Hall-voltage generator, small-signal amplifier, chopper stabilization, Schmitt trigger, and a current source output. Advanced BiCMOS wafer fabrication processing takes advantage of low-voltage requirements, component matching, very low input-offset errors and small component geometries. Suffix `L-' devices are rated for operation over a temperature range of -40C to +150C; suffix `E-' devices are rated for operation over a temperature range of -40C to +85C. Two A1242 package styles provide magnetically optimized solutions for most applications. Package LH is a SOT23W, a miniature low-profile surface-mount package, while package UA is a three-lead ultra-mini SIP for through-hole mounting. Each package is available lead (Pb) free, with 100% matte tin plated leadframes.
1 2 3
Package LH, 3-pin Surface Mount
3
1 2
NC 1 2
3
Package UA, 3-pin SIP
Features and Benefits
12 3
ABSOLUTE MAXIMUM RATINGS
Supply Voltage, VCC .......................................... 28 V Reverse-Supply Voltage, VRCC ........................ -18 V Magnetic Flux Density, B .........................Unlimited Operating Temperature Ambient, TA, Range E.................. -40C to 85C Ambient, TA, Range L................ -40C to 150C Maximum Junction, TJ(max)........................165C Storage Temperature, TS .................. -65C to 170C
Chopper stabilization - Superior temperature stability - Extremely low switchpoint drift - Insensitive to physical stress Reverse battery protection Solid-state reliability Small size Robust EMC capability High ESD ratings (HBM)
A1242-DS
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
A1242
Two-Wire Chopper-Stabilized Hall Effect Latch
Product Selection Guide
Part Number Packaging* Mounting 3-pin SOT23W surface mount 3-pin SIP through hole 3-pin SOT23W surface mount 3-pin SIP through hole A1242ELHLT-I1-T 7-in. reel, 3000 pieces/reel A1242ELHLT-I2-T A1242EUA-I1-T Bulk, 500 pieces/bag A1242EUA-I2-T A1242LLHLT-I1-T 7-in. reel, 3000 pieces/reel A1242LLHLT-I2-T A1242LUA-I1-T Bulk, 500 pieces/bag A1242LUA-I2-T *Contact Allegro for additional packing options. Low Current, ICC(L) (mA) 5.0 to 6.9 2.0 to 5.0 5.0 to 6.9 2.0 to 5.0 5.0 to 6.9 2.0 to 5.0 5.0 to 6.9 2.0 to 5.0 Ambient, TA (C) -40 to 85 -80 -40 to 150 80 BRP(MIN) (G) BOP(MAX) (G)
Functional Block Diagram
VCC
Regulator
To All Subcircuits Clock/Logic Sample and Hold Low-Pass Filter
Dynamic Offset Cancellation
Amp
GND Package UA Only
GND
Terminal List Name VCC GND NC Description Connects power supply to chip Ground No internal connection Number Package LH Package UA 1 1 3 2,3 2 -
A1242-DS
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
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A1242
Two-Wire Chopper-Stabilized Hall Effect Latch
ELECTRICAL CHARACTERISTICS over full operating voltage and temperature ranges, unless otherwise specified
Characteristic Electrical Characteristics Supply Voltage2 3 Supply Current Output Slew Rate4 Chopping Frequency Power-On Time Power-On State5 Supply Zener Clamp Voltage Supply Zener Current6 Reverse Battery Current Magnetic Characteristics7 Operate Point Release Point Hysteresis
1
Symbol VCC ICC(L) ICC(H) dI/dt fC tPO POS VZ(supply) IZ(supply) IRCC BOP BRP BHYS VCC > VCC(MIN)
Test Conditions Operating, TJ < 165C -I1, B < BRP -I2, B < BRP -I1 and -I2, B > BOP RS = 100 , CS = 20 pF, no bypass capacitor
Min. 3.5 5 2 12 - - - - 28 - - 5 -80 40
Typ.1 - - - - 36 200 - ICC(H) - - - 32 -32 64
Max. 24 6.9 5 17 - - 25 - - 20 2.5 80 -5 110
Units V mA mA mA mA/s kHz s - V mA mA G G G
tPO < tPO(max), dVCC / dt > 25 mV / s ICC = 20 mA; TA = 25C VS = 28 V VRCC = -18 V South pole adjacent to branded face of device North pole adjacent to branded face of device BOP - BRP
Typical values are at TA = 25C and VCC = 12 V. Performance may vary for individual units, within the specified maximum and minimum limits. 2 Maximum voltage must be adjusted for power dissipation and junction temperature; see Power Derating section. 3V CC represents the generated voltage between the VCC pin and the GND pin. 4 The value of dI is the difference between 90% of I CC(H) and 10% of ICC(L), and the value of dt is time period between those two points. The value of dI/dt depends on the value of the bypass capacitor, if one is used, with greater capacitances resulting in lower rates of change. 5 For t > t PO(max), and BRP < B < BOP, POS is undefined. 6 Maximum current limit is equal to the maximum I CCL(max) + 3 mA. 7 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) PERFORMANCE Contact Allegro for information.
A1242-DS
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
3
A1242
Two-Wire Chopper-Stabilized Hall Effect Latch
THERMAL CHARACTERISTICS may require derating at maximum conditions, see application information
Characteristic Symbol Test Conditions* Package LH, minimum-K PCB (single layer, single-sided with copper limited to solder pads) Package LH, low-K PCB (single layer, double-sided with 0.926 in2 copper area) Package UA, minimum-K PCB (single layer, single-sided with copper limited to solder pads) Value Units 228 110 165 C/W C/W C/W
Package Thermal Resistance
RJA
*Additional information available on the Allegro Web site.
Power Derating Curve TJ(max) = 165C; ICC = ICC(max)
25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 VCC(max)
Maximum Allowable VCC (V)
Low-K PCB, Package LH (R JA = 110 C/W) Minimum-K PCB, Package UA (R JA = 165 C/W) Minimum-K PCB, Package LH (R JA = 228 C/W) 20 40 60 80 100 120 140 160
VCC(min) 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
Power Dissipation, P D (mW)
Low-K PCB, Package LH (R JA = 110 C/W) Min-K PCB, Package UA (R JA = 165 C/W)
Min-K PCB, Package LH (R JA = 228 C/W)
20 40 60 80 100 120 140 160 180
Temperature (C)
A1242-DS
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
4
A1242
Two-Wire Chopper-Stabilized Hall Effect Latch Characteristic Data
Supply Current (Low) versus Ambient Temperature (1242- I1)
7.0 6.8 6.6 6.4
ICC(L) (mA)
ICC(L) (mA)
Supply Current (Low) versus Supply Voltage (A1242-I1)
7.0 6.8 6.6 6.4 Vcc (V) 24 12 3.75 6.2 6.0 5.8 5.6 5.4 5.2 5.0
TA (C) -40 25 85 150
6.2 6.0 5.8 5.6 5.4 5.2 5.0 -50 0 50
TA (C)
100
150
0
5
10 VCC (V)
15
20
25
Supply Current (Low) versus Ambient Temperature (1242- I2)
5.0 4.5
ICC(L) (mA)
Supply Current (Low) versus Supply Voltage (A1242-I2)
5.0 4.5
ICC(L) (mA)
4.0 3.5 3.0 2.5 2.0 -50 0 50
T A (C)
4.0 3.5 3.0 2.5 2.0
TA (C) -40 25 150
Vcc (V) 24 12 3.75
100
150
0
5
10 VCC (V)
15
20
25
Supply Current (High) versus Ambient Temperature
17 16
ICC(H) (mA) ICC(H) (mA)
17 16 15 14 13 12
Supply Current (High) versus Supply Voltage
15 14 13 12 -50 0 50 TA (C) 100 150 Vcc (V) 24 12 3.75
TA (C) -40 25 85 150
0
5
10 VCC (V)
15
20
25
A1242-DS
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
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A1242
Two-Wire Chopper-Stabilized Hall Effect Latch
Operate Point versus Ambient Temperature
80 65 50 35 20 5 -50 0 50 TA (C) 100 150 80 65
Operate Point versus Supply Voltage
B OP (G)
Vcc (V) 24 12 3.5
BOP (G)
50 35 20 5 0 5 10 VCC (V) 15 20 25
TA (C) -40 25 150
Release Point versus Ambient Temperature
-5 -20 -35 -50 -65 -80 -50 0 50 TA (C) 100 150 -5 -20
Release Point versus Supply Voltage
Vcc (V) 24 12 3.5
B RP (G)
BRP (G)
-35 -50 -65 -80 0 5 10 VCC (V) 15 20 25
TA (C) 150 25 -40
Hysteresis versus Ambient Temperature
110 100 90
Bhys (G) Bhys (G)
Hysteresis versus Supply Voltage
110 100 90 Vcc (V) 24 12 3.5 80 70 60 50 40
TA (C) -40 25 150
80 70 60 50 40 -50 0 50 TA (C) 100 150
0
5
10 VCC (V)
15
20
25
A1242-DS
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
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A1242
Two-Wire Chopper-Stabilized Hall Effect Latch Functional Description
OPERATION The output, ICC, of the A1242 switches to the high current state when a magnetic field perpendicular to the Hall sensor exceeds the operate point threshold, BOP. Note that the device latches, that is, a south pole of sufficient strength towards the branded surface of the device switches the device output to ICC(H). The device retains its output state if the south pole is removed. When the magnetic field is reduced to below the release point threshold, BRP, the device output goes to the low current state. The difference between the magnetic operate and release points is called the hysteresis of the device, BHYS. This built-in hysteresis allows clean switching of the output even in the presence of external mechanical vibration and electrical noise. . TYPICAL APPLICATION CIRCUIT The A1242 should be protected by an external bypass capacitor, CBYP, connected between the supply, VCC, and the ground, GND, of the device. CBYP reduces both external noise and the noise generated by the chopper-stabilization function. As shown in figure 2, a 0.01 F capacitor is typical. Installation of CBYP must ensure that the traces that connect it to the A1242 pins are no greater than 5 mm in length. All high-frequency interferences conducted along the supply lines are passed directly to the load through CBYP , and it serves only to protect the A1242 internal circuitry. As a result, the load ECU (electronic control unit) must have sufficient protection, other than CBYP, installed in parallel with the A1242. A series resistor on the supply side, RS (not shown), in combination with CBYP, creates a filter for EMI pulses. When determining the minimum VCC requirement of the A1242 device, the voltage drops across RS and the ECU sense resistor, RSENSE, must be taken into consideration. The typical value for RSENSE is approximately 100 .
GND A A B Package UA Only Maximum separation 5 mm
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 Products - SMD and Through-Hole, AN26009
All are provided in Allegro Electronic Data Book, AMS-702 and the Allegro Web site: www.allegromicro.com.
I+ ICC(H) Switch to High Switch to Low
ICC
ICC(L) 0 BOP B- 0 B+ BRP
BHYS
Figure 1. Switching Behavior of the A1242. 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).
V+
VCC
B
A1242
CBYP 0.01 uF
GND
B
RSENSE
ECU
Figure 2. Typical Application Circuit
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
7
A1242-DS
A1242
Two-Wire Chopper-Stabilized Hall Effect Latch
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 field induced signal to recover its original spectrum at baseband, while the dc offset becomes a high-frequency signal. The magnetic sourced signal then can pass through a low-pass filter, while the modulated dc offset is suppressed. This configuration is illustrated in Figure 3. 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 high frequency 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 Low-Pass Filter
Figure 3. Chopper stabilization circuit (dynamic quadrature offset cancellation)
Sample and Hold
A1242-DS
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
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A1242
Two-Wire Chopper-Stabilized Hall Effect Latch
Power Derating
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 minimum-K PCB. Observe the worst-case ratings for the device, specifically: RJA = 228C/W, TJ(max) = 165C, VCC(max) = 24 V, and ICC(max) = 17 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 = 66 mW Finally, invert equation 1 with respect to voltage: VCC(est) = PD(max) / ICC(max) = 66 mW / 17 mA = 3.9 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 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 = 6 mA, and RJA = 165 C/W, then: PD = VCC x ICC = 12 V x 6 mA = 72 mW T = PD x RJA = 72 mW x 165 C/W = 12C TJ = TA + T = 25C + 12C = 37C 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.
A1242-DS
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
9
A1242
Two-Wire Chopper-Stabilized Hall Effect Latch Package LH, 3-Pin (SOT-23W)
Package UA, 3-Pin
A1242-DS
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
10
A1242
Two-Wire Chopper-Stabilized Hall Effect Latch
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, Allegro MicroSystems, Inc.
A1242-DS
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
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