A3295_16 ALLEGRO
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Technical content
The A3295 Hall effect switch is an extremely temperature- stable and stress-resistant sensor IC unipolar switch, especially suited for operation over extended temperature ranges (up to 125°C). Superior high-temperature performance is made possible through Dynamic Offset Cancellation, which reduces the residual offset voltage normally caused by device package overmolding, temperature dependencies, and thermal stress. The device is not intended for automotive applications. The device includes, on a single silicon chip, a voltage regulator, a Hall-voltage generator, a small-signal amplifier, chopper stabilization, a Schmitt trigger, and a short-circuit protected open-drain output to sink up to 25 mA. A south polarity magnetic field of sufficient strength is required to turn the output on. An onboard regulator permits operation with supply voltages in the range of 3 to 24 volts. Two package styles provide a magnetically optimized package for most applications. Type LH is a miniature SOT23W low- profile surface-mount package, and type UA is a three-lead ultramini SIP for through-hole mounting. Both packages are lead (Pb) free, with 100% matte tin plated leadframes. A3295-DS, Rev. 11
- Resistant to physical stress
- Superior temperature stability
- Output short-circuit protection
- Operation from unregulated supply
- Reverse battery protection
- Solid-state reliability
- Small package size Chopper Stabilized, Precision Hall Effect Switch for Consumer and Industrial Applications Functional Block Diagram A3295 Amp Regulator Low-Pass Filter GND VCC OUT Control Current Limit Dynamic Offset Cancellation Sample and Hold Not to scale Packages: 3-Pin SOT23W (suffix LH) 3-Pin SIP (suffix UA) FEATURES AND BENEFITS DESCRIPTION
Chopper Stabilized, Precision Hall Effect Switch for Consumer and Industrial ApplicationsA3295 Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A. Selection Guide Part Number Packing1 Package Type Magnetic Switchpoints2 Operate, BOP (G) Release, BRP (G) A3295KLHLT-T 3000 pieces per 7-in. reel Surface mount SOT23W 75 max. 5 min.A3295KLHLX-T 10000 pieces per 13-in. reel Surface mount SOT23W A3295KUA-T 500 pieces per bulk bag Through hole ultramini SIP 1Contact Allegro for additional packing options. 21 G (gauss) = 0.1 mT (millitesla). 1 32 PTCT 1 2 PTCT Absolute Maximum Ratings Characteristic Symbol Notes Rating Units Supply Voltage VCC 26.5 V Reverse Battery Voltage VRCC –30 V Output Off Voltage VOUT 26 V Continuous Output Current IOUT Device provides internal current limiting to help protect itself from output short circuits 25 mA Reverse Output Current IROUT –50 mA Magnetic Flux Density B Unlimited G Operating Ambient Temperature TA Range K –40 to 125 ºC Maximum Junction Temperature TJ(max) 165 ºC Storage Temperature Tstg –65 to 170 ºC SPECIFICATIONS Terminal List Name Number FunctionLH UA VCC 1 1 Power supply OUT 2 3 Output GND 3 2 Ground Package LH, 3-Pin SOT23W Pin-out Diagram Package UA, 3-Pin SIP Pin-out Diagram
Chopper Stabilized, Precision Hall Effect Switch for Consumer and Industrial ApplicationsA3295 Allegro MicroSystems, LLC Worcester, Massachusetts 01615-0036 U.S.A. ELECTRICAL CHARACTERISTICS over operating temperature range, unless otherwise noted Characteristic Symbol Test Conditions Min. Typ.1 Max Units Supply Voltage Range2 VCC Operating, TJ < 165°C 3.0 – 24 V Output Leakage Current IOFF VOUT = 24 V, B < BRP – – 10 µA Output Saturation Voltage VOUT(SAT) IOUT = 20 mA, B > BOP – 185 500 mV Output Current Limit ION B > BOP 30 – 60 mA Power-On Time tPO VCC > 4.2 V – – 50 µs Chopping Frequency fC – 800 – kHz Output Rise Time tR RLOAD = 820 Ω, CLOAD = 20 pF – 0.2 2.0 µs Output Fall Time tF RLOAD = 820 Ω, CLOAD = 20 pF – 0.1 2.0 µs Supply Current ICC B < BRP , VCC = 12 V – 3.0 8.0 mA B > BOP , VCC = 12 V – 4.0 8.0 mA Reverse Battery Current IRCC VRCC = –30 V – – –5.0 mA Zener Voltage VZ + VD ICC = 15 mA, TA = 25°C 28 – – V Zener Impedance ZZ + ZD ICC = 15 mA, TA = 25°C – 50 – Ω 1Typical data at TA = 25°C, 12 V. 2Maximum VCC must be derated for power dissipation and junction temperature. See Application Information. MAGNETIC CHARACTERISTICS over VCC range, unless otherwise noted Characteristic Symbol Test Conditions Min. Typ. Max. Units Operate Point BOP – – 75 G Release Point BRP 5 – – G Hysteresis BHYS BOP – BRP – – 70 G
Chopper Stabilized, Precision Hall Effect Switch for Consumer and Industrial ApplicationsA3295 Allegro MicroSystems, LLC Worcester, Massachusetts 01615-0036 U.S.A. THERMAL CHARACTERISTICS may require derating at maximum conditions, see application information Characteristic Symbol Test Conditions* Value Units Package Thermal Resistance RθJA Package LH, 1-layer PCB with copper limited to solder pads 228 ºC/W Package LH, 2-layer PCB with 0.463 in.2 of copper area each side connected by thermal vias 110 ºC/W Package UA, 1-layer PCB with copper limited to solder pads 165 ºC/W *Additional thermal information available on Allegro website. 20 40 60 80 100 120 140 160 180 Temperature (ºC) Maximum Allowable VCC (V) Power Derating Curve (RθJA = 228 ºC/W) 1-layer PCB, Package LH (RθJA = 110 ºC/W) 2-layer PCB, Package LH (RθJA = 165 ºC/W) 1-layer 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) Power Dissipation versus Ambient Temperature (RθJA = 165 ºC/W) 1-layer PCB, Package UA (RθJA = 228 ºC/W) 1-layer PCB, Package LH θJA = 110 ºC/W) 2-layer PCB, Package LH
Chopper Stabilized, Precision Hall Effect Switch for Consumer and Industrial ApplicationsA3295 Allegro MicroSystems, LLC Worcester, Massachusetts 01615-0036 U.S.A. FUNCTIONAL DESCRIPTION Amp Regulator Low- Pass Filter Sample and Hold Figure 2: Chopper Stabilization Circuit (Dynamic Quadrature Offset Cancellation) Chopper-Stabilized Technique The Hall element can be considered as a resistor array similar to a Wheatstone bridge. A basic circuit is shown in figure 1, demonstrating the effect of the magnetic field flux density, B, impinging on the Hall element. When using Hall effect tech- nology, a limiting factor for switchpoint accuracy is the small signal voltage, V HALL, developed across the Hall element. This voltage is disproportionally small relative to the offset that can be produced at the output of the Hall device, caused by device overmolding, temperature dependencies, and thermal stress. A large portion of the offset is a result of the mismatching of these resistors. The A3295 uses a proprietary dynamic offset cancellation technique, with an internal high-frequency clock, to reduce the residual offset, see figure 2. The chopper-stabilizing technique cancels the mismatching of the resistor circuit by changing the direction of the current flowing through the Hall element. To do so, CMOS switches and Hall voltage measure- ment taps are used, while maintaining V HALL signal that is induced by the external magnetic flux. The signal is then captured by a sample-and-hold circuit and fur- ther processed using low-offset bipolar circuitry. This technique produces devices that have an extremely stable quiescent Hall output voltage, are immune to thermal stress, and have precise recoverability after temperature cycling. This technique will also slightly degrade the device output repeatability. A relatively high sampling frequency is used in order to process faster signals. More detailed descriptions of the circuit operation can be found on the Allegro Web site, including: Technical Paper STP 97-10, Monolithic Magnetic Hall Sensing Using Dynamic Quadrature Offset Cancellation, and Technical Paper STP 99-1, Chopper- Stabilized Amplifiers with a Track-and-Hold Signal Demodula- tor. Operation The output of the A3295 switches low (turns on) when a mag- netic field perpendicular to the Hall element transitions through and exceeds the Operate Point threshold, B OP. This is illus- trated in figure 3. After turn-on, the output is capable of sinking 25 mA, and the output voltage reaches V OUT(SAT). Note that after a south (+) polarity magnetic field of sufficient strength impinging on the branded face of the device turns on the device, the device remains on until the magnetic field is reduced below the Release Point threshold, B RP . At that transi- tion, the device output goes high (turns off). The difference in the magnetic operate and release points is the hysteresis, B HYS, of the device. This built-in hysteresis allows clean switching of the output, even in the presence of external mechanical vibration and electrical noise. BOP BRP BHYS VOUT(off) VOUT VOUT(on)(sat) Switch to Low Switch to High Hysteresis of ∆VOUT Switching Due to ∆B Figure 3: Output Voltage Responds to Magnetic Flux Density. Figure 1: Hall Element, Basic Circuit Operation +VCC B –VHALL +VHALL
Chopper Stabilized, Precision Hall Effect Switch for Consumer and Industrial ApplicationsA3295 Allegro MicroSystems, LLC Worcester, Massachusetts 01615-0036 U.S.A.
APPLICATION INFORMATION
When the device is powered on, if the ambient magnetic field has an intensity that is between BOP and BRP , the initial output state is indeterminate. The first time that the level of B either rises through BOP , or falls through BRP , however, the correct output state is obtained. 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. This configuration is shown in figure 4. The simplest form of magnet that will operate these devices is a ring magnet. Other methods of operation, such as linear magnets, are possible. The device must be operated below the maximum junction temperature of the device, T J(max). Under certain combinations of peak conditions, reliable operation may require derating supplied power or improving the heat dissipation properties of the applica- tion. The Package Thermal Resistance, RθJA, is a figure of merit summarizing the ability of the application and the device to dissi- pate 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. Sample power dissipation results are given in the Thermal Characteristics section. Additional thermal data is also available on the Allegro website. Extensive applications information for Hall-effect devices is available in: Hall-Effect IC Applications Guide, Application Note 27701 and Guidelines for Designing Subassemblies Using Hall- Effect Devices, Application Note 27703.1 Figure 4: Typical Basic Application Circuit A bypass capacitor is highly recommended. VCC A3295 VOUT VCC GND0.1 uF
Chopper Stabilized, Precision Hall Effect Switch for Consumer and Industrial ApplicationsA3295 Allegro MicroSystems, LLC Worcester, Massachusetts 01615-0036 U.S.A. Figure 5: Package LH, 3-Pin SOT23W A B C D C For Reference Only – Not for Tooling Use (Reference DWG-2840) Dimensions in millimeters– NOTT O SCALE Dimensions exclusive of mold flash, gate burrs, and dambar protrusions Exact case and lead configuration at supplier discretion within limits shown 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 Active Area Depth, 0.28 mm Hall elements, not to scale =T emperature Code (Letter)T Standard Branding Reference View NNT Branding scale and appearance at supplier discretion Seating Plane Gauge Plane PCB Layout Reference View
0.55 REF
0.25 BSC
0.95 BSC
0.95 1.00 0.70 2.40 B A Branded Face 2.90 +0.10 –0.20 4° ±4° 8X 10° REF 0.180 +0.020 –0.053 0.05 +0.10 –0.05
0.25 MIN
1.91 +0.19 –0.06 2.98 +0.12 –0.08 1.00 ±0.13 0.40 ±0.10 D D D 1.49 0.96 = Last three digits of device part numberN NNN = Last three digits of device part numberN A1101, A1102, A1103, A1104, and A1106 A1101, A1102, A1103, and A1104, only CUSTOMER PACKAGE DRAWINGS
Chopper Stabilized, Precision Hall Effect Switch for Consumer and Industrial ApplicationsA3295 Allegro MicroSystems, LLC Worcester, Massachusetts 01615-0036 U.S.A. Figure 6: Package UA, 3-Pin SIP For Reference Only – Not for Tooling Use (Reference DWG-9049) Dimensions in millimeters – NOT TO SCALE Dimensions exclusive of mold flash, gate burrs, and dambar protrusions Exact case and lead configuration at supplier discretion within limits shown 231
1.27 NOM
2.16 MAX
0.51 REF
0.79 REF
B A B C A D E D E E 2.04 1.44 E Branding scale and appearance at supplier discretion Hall element, not to scale Mold Ejector Pin Indent Branded Face 4.09+0.08 –0.05 0.41 +0.03 –0.06 3.02+0.08 –0.05 0.43+0.05 –0.07 15.75 ±0.25 Dambar removal protrusion (6X) Gate and tie bar burr area Active Area Depth, 0.50 mm REF NNT Standard Branding Reference View = Supplier emblem = Last three digits of device part number =T emperature code N 45° C 45°
2 X 10°
1.52 ±0.05 T
Chopper Stabilized, Precision Hall Effect Switch for Consumer and Industrial ApplicationsA3295 Allegro MicroSystems, LLC Worcester, Massachusetts 01615-0036 U.S.A. Copyright ©2005-2015, Allegro MicroSystems, LLC Allegro MicroSystems, LLC 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, LLC 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
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