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description the A1425 ac-coupled hall-effect sensor ic is a monolithic integrated circuit that switches in response to changing differential magnetic fields created by rotating ring magnets and, when coupled with a magnet, by ferrous targets. the device is a true zero-crossing detector: the output switches precisely when the difference in magnetic field strength between the two hall elements is zero. a unique dual-comparator scheme provides for accurate switching at the zero crossing on both the positive and negative-going regions of the differential signal, while utilizing hysteresis to prevent false switching. the zero- crossing nature of this device provides excellent repeatability and accuracy for crankshaft applications. changes in field strength at the device face, which are induced by a moving target, are sensed by the two integrated hall transducers. the transducers generate signals that are differentially amplified by on-chip electronics. this differential design provides immunity to radial vibration within the operating air gap range of the A1425, by rejection of the common mode signal. steady-state magnet and system offsets are eliminated using an on-chip differential band-pass filter. this filter also provides relative immunity to interference from electromagnetic sources. 1425-dsa, rev.3 features and benefits ? used in sensing motion of ring magnet or ferrous targets ? integrated filter capacitor ? wide operating temperature range ? operation with magnetic input signal frequency from 20 hz to 20 khz ? resistant to emi ? large effective air gaps ? 4.0 to 26.5 v supply operating range ? output compatible with both ttl and cmos logic families ? reverse battery protection ? resistant to mechanical and thermal stress ? accurate true zero-crossing switchpoint high accuracy analog speed sensor ic with integrated filter capacitor and dual zero-crossing output signal continued on the next page? package: 4 pin sip (suffix k) functional block diagram A1425 hall amp regulator bandpass filter integrated tracking capacitor vout (pin 2 ) vcc (pin 1) gnd (pin 4) 0.1 uf v s + diagnostic circuitry gain stage dual hall transducers comparator test (pin 3) (required) v ref
high accuracy analog speed sensor ic with integrated filter capacitor and dual zero-crossing output signal A1425 2 allegro microsystems, inc. 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com the device utilizes advanced temperature compensation for the high-pass lter, sensitivity, and schmitt trigger switchpoints, to guarantee optimal operation to low frequencies over a wide range of air gaps and temperatures. each hall effect digital integrated circuit includes a voltage regulator, two hall effect elements, temperature compensating circuitry, a low-level ampli er, band-pass lter, schmitt trigger, and an output driver, which requires a pull-up resistor. the on- board regulator permits operation with supply voltages from 4.0 to 26.5 v. the output stage can easily switch 20 ma over the full frequency response range of the device, and is compatible with both ttl and cmos logic circuits. the device is packaged in a 4-pin plastic sip. it is lead (pb) free, with 100% matte tin plated leadframe. 2 34 1 terminal list table name number vcc 1 vout 2 test 3 gnd 4 pin-out diagram selection guide part number packing * switchpoints b rp(min) (g) b op(max) (g) A1425lk-t bulk, 500 pieces/bag ?11 11 * contact allegro for additional packing options. absolute maximum ratings characteristic symbol notes rating units supply voltage v cc refer to power derating section 28 v reverse supply voltage v rcc ?18 v continuous output current i out 25 ma continuous reverse-output current i rout ?50 ma operating ambient temperature t a range l ?40 to 150 oc maximum junction t j(max) 165 oc storage temperature t stg ?65 to 170 oc description (continued)
high accuracy analog speed sensor ic with integrated filter capacitor and dual zero-crossing output signal A1425 3 allegro microsystems, inc. 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com operating characteristics valid at t a = ? 40 o c to 150 o c, t j 165c; over operational air gap range and v cc within operating range, unless otherwise noted. typical operating parameters: v cc = 12 v and t a = 25c. characteristic symbol test conditions min. typ. max. units electrical characteristics supply voltage v cc operating; t j < t j(max) 4.0 ? 26.5 v supply current i cc ? 4.2 7.0 ma output saturation voltage v out(sat) i sink = 20 ma ? 140 400 mv output leakage current i off v out = 24 v, b diff = 0 ? ? 5 a protection component characteristics reverse supply current i rcc v cc = ?18 v ? ? ?1 ma supply zener current i zsupply v s = 28 v ? ? 10 ma supply zener clamp voltage 1 v zsupply i cc = 10 ma, t a = 25c 28 33 37 v output zener current i zoutput v out = 28 v ? ? 3 ma output zener clamp voltage v zoutput i out = 3 ma, t a = 25c 28 ? ? v output short circuit current limit 2 i outs(lim) ? ? 50 ma response characteristics power-on state pos t < t response ? high ? v power-on time 3,7 t po v cc > v cc(min) ? 4.5 9 ms settling time 4,7 t settle f bdiff 100 hz 0 ? 50 ms response time 7 t response equal to t po + t s ; f bdiff 100 hz 4.5 ? 59 ms upper corner frequency f cu ?3 db, single pole 20 ? ? khz lower corner frequency f cl ?3 db, single pole ? ? 20 hz output characteristics output rise time 5 t r r pu = 1 k , c out2 = 10 pf ? ? 200 ns output fall time t f r pu = 1 k , i sink = 20 ma, c out2 = 10 pf ? ? 200 ns magnetic characteristics output off switchpoint 6,7 b op b diff increasing, f bdiff = 200 hz, b diff = 50 gp-p; digital output signal switches low to high ?11 0 11 g output on switchpoint 6,7 b rp b diff decreasing, f bdiff = 200 hz, b diff = 50 gp-p; digital output signal switches high to low ?11 0 11 g applied magnetic field 7,8 b diff differential p-p magnetic eld 50 ? 1250 g 1 i cc equivalent to i cc(max) + 3 ma. 2 i out does not change state when i out > i outs(lim) , regardless of changes in the impinging magnetic eld. 3 time required to initialize device. 4 time required for the output switchpoints to be within speci cation. 5 output rise time will be dominated by the rc time constant. 6 for other sinusoidal signal frequencies and magnetic elds, ?b op = b rp = sin (b diff 2) 25%, where is the phase shift shown in the characteristic data section. 7 see de nitions of terms section. 8 exceeding the maximum magnetic eld may result in compromised absolute accuracy.
high accuracy analog speed sensor ic with integrated filter capacitor and dual zero-crossing output signal A1425 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 rating units package thermal resistance r ja single-layer pcb, with copper limited to solder pads 177 oc/w 20 40 60 80 100 120 140 160 180 temperature (oc) maximum allowable v cc (v) power derating curve 8 10 12 14 0 2 4 6 16 18 20 22 24 26 28 30 (r ja = 177 oc/w) v cc(min) v cc(max) temperature (c) power dissipation, p d (m w) 20 40 60 80 100 120 140 160 180 maximum power dissipation, p d(max) (r ja = 177 oc/w) 0 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 800 850 900 de nitions of terms the following provide additional information about some of the parameters cited in the operating characteristics table. for additional information, visit the allegro web site at www.allegromicro.com . applied magnetic field, b diff ? the differential magnetic ux density which is calculated as the arithmetic difference of the ux densities observed by each of the two hall elements. output off switchpoint (operate point), b op ? the value of increasing differential magnetic ux density at which the device output switches from low to high. this value may be greater than or less than 0 g. output on switchpoint (release point), b rp ? the value of decreasing differential magnetic ux density at which the device output switches from high to low. this value may be greater than or less than 0 g. power-on time, t po ? the time needed by the device, after power is applied, to initialize all circuitry necessary for proper operation. settling time, t settle ? the time required by the device, after t po , and after a valid magnetic signal has been applied, to provide proper output transitions. settling time is a function of magnetic offset, offset polarity, signal phase, signal frequency, and signal amplitude. response time t response ? the total time required for generat- ing zero-crossing output transitions after power-up (the sum of power-on time and settling time).
high accuracy analog speed sensor ic with integrated filter capacitor and dual zero-crossing output signal A1425 5 allegro microsystems, inc. 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com empirical results 4.5 20.0 12.0 v cc (v) 4.5 20.0 12.0 v cc (v) 150 ?40 25 t a (oc) v cc (v) v cc (v) 0 5 10 15 20 25 supply current by ambient temperature t a (oc) i cc (ma) ?50 0 50 100 150 200 supply current by supply voltage i cc (ma) 0102030 output voltage by ambient temperature t a (oc) v out(sat) (mv) 500 450 400 350 300 250 200 150 100 50 0 ?50 0 50 100 150 200 i sink = 20 ma output voltage by supply voltage v out(sat) (mv) 500 450 400 350 300 250 200 150 100 50 0 i sink = 20 ma 7 6 5 4 3 2 1 0 4.5 26 12 v cc (v) 7 6 5 4 3 2 1 0 150 ?40 25 t a (oc) continued on next page .
high accuracy analog speed sensor ic with integrated filter capacitor and dual zero-crossing output signal A1425 6 allegro microsystems, inc. 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com empirical results, continued air gap (mm) repeatability (o of rotation) 116 air gap (mm) repeatability (o of rotation) 116
high accuracy analog speed sensor ic with integrated filter capacitor and dual zero-crossing output signal A1425 7 allegro microsystems, inc. 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com simulation results A1425 minimum switching fields over the range of ambient operating temperatures, t a f bdiff(low) = 15 hz, f bdiff(high) 30 khz b diff(min) (g) frequency, f bdiff (khz) 0.01 0.1 1 10 40 40 0 35 5 30 10 25 15 20 150 25 ?40 A1425 typical phase shift over the range of applied magnetic fields, b diff f bdiff(low) = 15 hz, f bdiff(high) = 30 khz phase shift (o) frequency, f bdiff (khz) 0.01 0.1 1 10 40 40 0 30 ?30 20 ?50 ?60 ?40 ?20 10 ?10 50 100 500 1250 750 b diff in gp-p continued on next page .
high accuracy analog speed sensor ic with integrated filter capacitor and dual zero-crossing output signal A1425 8 allegro microsystems, inc. 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com simulation results, continued 50 100 500 750 125 0 i out delay ( s) i out lagging i out leading frequency, f bdiff (khz) 0.1 1 10 40 20 ?20 15 ?15 10 ?10 5 ?5 0 A1425 typical delay over the range of applied magnetic fields, b diff f bdiff(low) = 15 hz, f bdiff(high) = 30 khz b diff in gp-p 50 100 500 750 1250 i out delay ( s) i out lagging i out leading frequency, f bdiff (hz) 0 100 1000 0 ?1000 ?2000 ?3000 ?4000 ?5000 ?6000 A1425 typical delay over the range of applied magnetic fields, b diff f bdiff(low) = 15 hz, f bdiff(high) = 30 khz b diff in gp-p positive values of delay indicate a lagging output, while negative values indicate a leading output. positive values of delay indicate a lagging output, while negative values indicate a leading output.
high accuracy analog speed sensor ic with integrated filter capacitor and dual zero-crossing output signal A1425 9 allegro microsystems, inc. 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com A1425 v s c1 r1 1 vcc 3 test vout gnd 2 4 r pu c out2 (required) device evaluation: emc characterization test name reference speci cation esd ? human body model* aec-q100-002 esd ? machine model* aec-q100-003 conducted transients iso 7637-1 direct rf injection iso 11452-7 bulk current injection iso 11452-4 tem cell iso 11452-3 * esd testing is performed with no external components. please contact allegro microsystems for emc performance information. component value units r pu a 1.2 k r1 b 100 c1 0.1 f c out c 4.7 nf a pull-up resistor not required for protection but for normal operation. b for improved ci performance c for improved bci performance recommended emc test circuit.
high accuracy analog speed sensor ic with integrated filter capacitor and dual zero-crossing output signal A1425 10 allegro microsystems, inc. 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com the A1425 is a versatile high-precision differential hall-effect device that can be used in a wide range of applications. proper choice of the target material and shape, and assembly techniques enables large working air gaps and high switchpoint accuracy over the device operating temperature range. device operation the A1425 sensor ic contains two integrated hall transducers that are used to differentially respond to a magnetic eld across the surface of the ic. referring to gure 1, the trigger switches the output off (output high) when the differential magnetic eld crosses zero while increasing in strength (referred to as the posi- tive direction), and switches the output on (output low) when the differential magnetic eld crosses zero while decreasing (the negative direction). the operation is achieved through the use of two separate com- parators. both comparators use the same reference point, 0 g, to provide high accuracy, but one comparator has a positive hyster- esis, b hys1 , and the other a negative hysteresis, b hys2 . therefore, one comparator switches (b op ) at the zero crossing on an increas- ing differential signal and the other switches (b rp ) at the zero crossing on a decreasing differential signal. the hysteresis on each comparator precludes false switching on noise or target jitter. start-up during power-on time, t po , the output signal, v out , is high. beyond this time, if the applied magnetic eld, b diff , is absent or less than 50 g peak-to-peak, the switching state and v out polar- ity are indeterminate. v out will be valid for b diff > 50 gp-p, after the additional settling time, t settle , has also elapsed. also during t po , a circuit in the A1425 is brie y enabled that charges the on- chip capacitor. this feature reduces t po , relative to the long rc time constant of a high-pass lter. delay the on-chip band-pass lter induces delay in the output signal, v out , relative to the applied magnetic eld, b diff . simulation data shown in the characteristic data section quantify the effect of the input signal amplitude on the phase shift of the output. ac-coupled operation steady-state magnet and system offsets are eliminated using an on-chip differential band-pass lter. the low and high frequency poles of this band-pass lter are set using internal integrated capacitors and resistors. the differential structure of this lter improves the ability of the ic to reject single-ended noise on the ground (gnd pin) or supply line (vcc pin) and, as a result, makes it more resistant to electromagnetic interference typically seen in hostile remote-sensing environments. functional description figure 1. typical output characteristics with dual comparator operation. characteristics shown without delay, see characteristi c data section charts for delay and phase shift contributions. 11.0 0.0 ?11.0 on off off b rp(typ) b op(typ) b op(min) / b rp(min) b op(max) / b rp(max) output signal, v out switching state applied magnetic field, b diff comparator 1 comparator 2 t+ b hys2 ? b hys1 ?
high accuracy analog speed sensor ic with integrated filter capacitor and dual zero-crossing output signal A1425 11 allegro microsystems, inc. 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com target selection the zero-crossing switchpoints and ac-coupled operation of this device make target selection important. for high-density target geometries or small target features that produce a sinusoidal magnetic signal, the high-pass lter is capable of ltering offsets that may be induced in the nal device output. if such offset is present, and the target has larger features, then the high-pass lter may not be effective at higher speeds and an accuracy shift may occur. these relationships are shown in gure 2. power supply protection the A1425 contains an on-chip voltage regulator and can oper- ate over a wide supply voltage range. in applications that operate the device from an unregulated power supply, transient protec- tion must be added externally. for applications using a regulated line, emi/rfi protection may still be required. the circuit shown in gure 3 is the most basic con guration required for proper device operation. applications information 2 1 3 (required) 4 v out 0.1 uf r pu vcc A1425 figure 3. basic application circuit. a pull-up resistor, r pu , is required with the output driver. +b +v 0 0 0 ?b differential magnetic flux density, b diff device output voltage, v out t +b output edge shift +v 0 ?b differential magnetic flux density, b diff device output voltage, v out t valley large feature (tooth) figure 2. large feature effects. (a) large target feature but no device offset, normal edge position. (b) large target feature with negative device offset, shifted (advanced) output edge position. (a) (b)
high accuracy analog speed sensor ic with integrated filter capacitor and dual zero-crossing output signal A1425 12 allegro microsystems, inc. 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com power derating the device must be operated below the maximum junction temperature of the device, t j (max). under certain combina- tions 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 t j . (thermal data is also available on the allegro microsystems web site.) the package thermal resistance, r ? ja , is a gure 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 ? jc , is relatively small component of r ? ja . ambient air temperature, t a , and air motion are signi cant external factors, damped by overmolding. the effect of varying power levels (power dissipation, p d ), can be estimated. the following formulas represent the fundamental relationships used to estimate t j , at p d . p d = v in i in (1) ? ???????????????????????? t = p d r ? ja (2) t j = t a + t (3) for example, given common conditions such as: t a = 25c, v cc = 5.0 v, i cc = 4.2 ma, and r ? ja = 177 c/w, then: p d = v cc i cc = 5.0 v 4.2 ma = 21.0 mw ?? t = p d r ? ja = 21.0 mw 177 c/w = 3.7c t j = t a + ? t = 25c + 3.7c = 28.7c a worst-case estimate, p d (max), represents the maximum allow- able power level (v cc (max), i cc (max)), without exceeding t j (max), at a selected r ? ja and t a . example reliability for v cc at t a = 150c, using minimum-k pcb observe the worst-case ratings for the device, speci cally: r ? ja = 177c/w, t j (max) = 165c, v cc (max) = 26.5 v, and i cc (max) = 7.0 ma. calculate the maximum allowable power level, p d (max). first, invert equation 3: ? t max = t j (max) ? t a = 165 c ? 150 c = 15 c this provides the allowable increase to t j resulting from internal power dissipation. then, invert equation 2: ???? p d (max) = ? t max r ? ja = 15c 177 c/w = 84 mw finally, invert equation 1 with respect to voltage: v cc(est) = p d (max) i cc (max) = 84 mw 7.0 ma = 12 v the result indicates that, at t a , the application and device can dissipate adequate amounts of heat at voltages v cc(est) . compare v cc(est) to v cc (max). if v cc(est) v cc (max), then reli- able operation between v cc(est) and v cc (max) requires enhanced r ? ja . if v cc(est) v cc (max), then operation between v cc(est) and v cc (max) is reliable under these conditions. for example, when a standard diode with a 0.7 v drop is used: v s (max) = 12 v + 0.7 v = 12.7 v
high accuracy analog speed sensor ic with integrated filter capacitor and dual zero-crossing output signal A1425 13 allegro microsystems, inc. 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com package k, 4-pin sip 24 3 1 e1 e2 2.20 1.50 0.84 ref 1.27 nom 2.16 max 45 45 d active area depth, .0.42 mm hall elements (e1 and e2); not to scale d e e e e b 1.29 gate and tie bar burr area a b c dambar removal protrusion (8x) a d for reference only; not for tooling use (reference dwg-9010) 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 n = device part number y = last two digits of year of manufacture w = week of manufacture mold ejector pin indent branded face yyww nnnn 1 5.21 +0.08 ?0.05 0.38 +0.06 ?0.03 3.43 +0.08 ?0.05 0.41 +0.07 ?0.05 14.73 0.51 1.55 0.05 branding scale and appearance at supplier discretion copyright ?2005-2008, allegro microsystems, inc. 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 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

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