description 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 125c). 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 4.2 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. 7 features and benefits ? 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 1 7 dynamic offset cancellation sample and hold not to scale packages: 3 pin sot23w (suffix lh), and 3 pin sip (suffix ua)
chopper stabilized, precision hall effect switch for consumer and industrial applications A3295 2 allegro microsystems, inc. 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com selection guide part number packing 1 package type magnetic switchpoints 2 operate, b op (g) release, b rp (g) A3295klhlt-t 3000 pieces per 7-in. reel surface mount sot23w 75 max. 5 min. A3295kua-t 500 pieces per bulk bag through hole ultramini sip 1 contact allegro for additional packing options. 2 1 g (gauss) = 0.1 mt (millitesla). pin-out diagrams terminal list name number function lh ua vcc 1 1 power supply out 2 3 output gnd 3 2 ground package lh 1 3 2 ptct 1 2 3 ptct package ua absolute maximum ratings characteristic symbol notes rating units supply voltage v cc 26.5 v reverse battery voltage v rcc ?30 v output off voltage v out 26 v continuous output current i out device provides internal current limiting to help protect itself from output short circuits 25 ma reverse output current i rout ?50 ma magnetic flux density b unlimited g operating ambient temperature t a range k ?40 to 125 oc maximum junction temperature t j (max) 165 oc storage temperature t stg ?65 to 170 oc
chopper stabilized, precision hall effect switch for consumer and industrial applications A3295 3 allegro microsystems, inc. 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com electrical characteristics over operating temperature range, unless otherwise noted characteristic symbol test conditions min. typ. 1 max units supply voltage range 2 v cc operating, t j < 165c 4.2 ? 24 v output leakage current i off v out = 24 v, b < b rp ??10 a output saturation voltage v out(sat) i out = 20 ma, b > b op ? 185 500 mv output current limit i on b > b op 30 ? 60 ma power-on time t po v cc > 4.2 v ? ? 50 s chopping frequency f c ? 800 ? khz output rise time t r r load = 820 , c load = 20 pf ? 0.2 2.0 s output fall time t f r load = 820 , c load = 20 pf ? 0.1 2.0 s supply current i cc b < b rp , v cc = 12 v ? 3.0 8.0 ma b > b op , v cc = 12 v ? 4.0 8.0 ma reverse battery current i rcc v rcc = ?30 v ? ? ?5.0 ma zener voltage v z + v d i cc = 15 ma, t a = 25c 28 ? ? v zener impedance z z + z d i cc = 15 ma, t a = 25c ? 50 ? 1 typical data at t a = 25c, 12 v. 2 maximum v cc must be derated for power dissipation and junction temperature. see application information. magnetic characteristics over v cc range, unless otherwise noted characteristic symbol test conditions min. typ. max. units operate point b op ? ? 75 g release point b rp 5??g hysteresis b hys b op ? b rp ? ? 70 g
chopper stabilized, precision hall effect switch for consumer and industrial applications A3295 4 allegro microsystems, inc. 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com thermal characteristics may require derating at maximum conditions, see application information characteristic symbol test conditions* value units package thermal resistance r ja 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. 6 7 8 9 2 3 4 5 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 20 40 60 80 100 120 140 160 180 temperature (oc) maximum allowable v cc (v) power derating curve (r q ja = 228 oc/w) 1-layer pcb, package lh (r q ja = 110 oc/w) 2-layer pcb, package lh (r q ja = 165 oc/w) 1-layer pcb, package ua v cc(min) v cc(max) 0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 20 40 60 80 100 120 140 160 180 temperature (c) power dissipation, p d (m w) power dissipation versus ambient temperature (r ja = 165 oc/w) 1-layer pcb, p a ckage u a (r ja = 22 8 o c /w ) 1-layer pc b, pa cka ge lh (r j a = 110 oc/w) 2-layer pcb, packag e lh
chopper stabilized, precision hall effect switch for consumer and industrial applications A3295 5 allegro microsystems, inc. 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com 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) . b op b rp b hys v out(off) v out v out(on)(sat) switch to low switch to high b+ v+ hysteresis of v out switching due to b figure 3. output voltage responds to magnetic flux density. figure 1. hall element, basic circuit operation +v cc b ? v hall +v hall
chopper stabilized, precision hall effect switch for consumer and industrial applications A3295 6 allegro microsystems, inc. 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com application information 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 transition, the device output goes high (turns off). the difference in the mag- netic 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. when the device is powered on, if the ambient magnetic field has an intensity that is between b op and b rp , the initial output state is indeterminate. the first time that the level of b either rises through b op , or falls through b rp , 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, r ? ja , 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 ? jc , is relatively small component of r ? ja . ambient air temperature, t a , 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 v cc gnd 0.1 uf
chopper stabilized, precision hall effect switch for consumer and industrial applications A3295 7 allegro microsystems, inc. 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com package lh, 3-pin sot23w 0.55 ref gauge plane seating plane 0.25 bsc 0.95 bsc 0.95 1.00 0.70 2.40 2 1 a active area depth, 0.28 mm ref b c 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 branding scale and appearance at supplier discretion a pcb layout reference view branded face c standard branding reference view n = last two digits of device part number t = temperature code (letter) 1 nnt n = last three digits of device part number 1 nnn 2.90 +0.10 ?0.20 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 44 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 d hall element, not to scale d d d 1.49 0.96 3
chopper stabilized, precision hall effect switch for consumer and industrial applications A3295 8 allegro microsystems, inc. 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com package ua, 3-pin sip 23 1 0.79 ref 1.27 nom 2.16 max 0.51 ref 45 c 45 b e e e 2.06 1.45 gate burr area a b c dambar removal protrusion (6x) a d e d branding scale and appearance at supplier discretion hall element, not to scale active area depth, 0.50 mm ref for reference only; not for tooling use (reference dwg-9049) dimensions in millimeters dimensions exclusive of mold flash, gate burrs, and dambar protrusions exact case and lead configuration at supplier discretion within limits shown standard branding reference view = supplier emblem n = last two digits of device part number t = temperature code nnt 1 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 0.51 1.52 0.05
chopper stabilized, precision hall effect switch for consumer and industrial applications A3295 9 allegro microsystems, inc. 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com copyright ?2005-2012, allegro microsystems, inc. 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 per- mit 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?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 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. for the latest version of this document, visit our website: www.allegromicro.com revision history revision revision date description of revision rev. 7 may 24, 2012 update lh package branding
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