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description the A1421, a1422, and a1423 are ac-coupled hall-effect sensor ics which include monolithic integrated circuits that switch in response to changing differential magnetic fields created by rotating ring magnets or, when coupled with a magnet, by ferrous targets. this family of devices also includes an integrated capacitor that provides the high accuracy of analog sensing without an external filter capacitor. this reduces cost and components, while improving the reliability of the final sensor solution. magnetic field changes affect the two integrated hall transducers and then are differentially amplified on the chip. differential design provides immunity to radial vibration, within the device operating air gap range, by rejection of this common-mode signal change. steady-state system offsets are eliminated using an on-chip differential bandpass filter with integrated capacitor. this filter also provides relative immunity to interference from electromagnetic sources. the device utilizes advanced temperature compensation for the high-pass filter, sensitivity, and schmitt trigger switchpoints to guarantee optimal operation to low frequencies over a wide range of air gaps and temperatures. A1421a-ds, rev. 4 features and benefits ? integrated tracking capacitor ? used for sensing motion of ring magnet or ferrous targets ? wide operating temperature range ? operation with magnetic input signal frequency from 20 hz to 30 khz ? emi/esd-resistant ? large effective air gaps ? 4.0 to 26.5 v supply operating range ? output compatible with cmos logic families ? reverse battery protection ? resistant to mechanical and thermal stress ? accurate true zero crossing switchpoint (A1421 only) ? high vibration immunity, in running mode (a1423 only) high precision hall effect ac-coupled differential sensor ic with integrated filter capacitor continued on the next page? package: 4 pin sip (suffix k) functional block diagram not to scale A1421, a1422, and a1423 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 precision hall effect ac-coupled differential sensor ic with integrated filter capacitor A1421, a1422, and a1423 2 allegro microsystems, inc. 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com each device includes: a voltage regulator, two hall transduc- ers, temperature compensating circuitry, a low-level ampli- fier, bandpass filter, schmitt trigger, and an output driver. the on-board regulator permits operation with supply voltages from 4.0 to 26.5 v. the output stage can switch 20 ma over the full frequency response range of the device, and is compatible with cmos logic circuits. the devices in this family differ from each other in their switchpoint specifications and their switching polarity. the A1421 has a small hysteresis and asymmetrical switchpoints, with one switchpoint at the zero-crossing. the a1422 has a small hysteresis and symmetrical switchpoints, both near the zero- crossing. the a1423 offers high vibration immunity, by means of its larger hysteresis that establishes symmetrical switchpoints pin-out diagram 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 output current i out 25 ma reverse-output current i rout ?50 ma operating ambient temperature t a range l ?40 to 150 oc maximum junction temperature t j(max) 165 oc storage temperature t stg ?65 to 170 oc terminal list table number name 1 vcc 2 vout 3 test 4 gnd description (continued) product selection guide part number output switching at b diff = 0 switchpoints symmetry packing * b diff increasing b diff decreasing b op(typ) (g) b rp(typ) (g) b op(max) + b rp(min) (g) b op(typ) + b rp(typ) (g) b op(min) + b rp(max) (g) A1421lk-t low (on) to high (off) high (off) to low (on) 15 0 15 15 7.5 bulk, 500 pieces/bag a1422lk-t high (off) to low (on) low (on) to high (off) 15 ?15 0 0 0 a1423lk-t high (off) to low (on) low (on) to high (off) 65 ?65 0 0 0 * contact allegro for additional packing options. 2 34 1 continued on the next page?
high precision hall effect ac-coupled differential sensor ic with integrated filter capacitor A1421, a1422, and a1423 3 allegro microsystems, inc. 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com further from the zero-crossing. the output polarities are shown in the product selection guide table. this variety of options provides flexibility for achieving solu- tions for a wide range of applications, including automotive transmission and crankshaft speed sensing. the device package has an operating ambient temperature range ?40c to 150c , and is provided in a 4-pin plastic sip. each package is available in a lead (pb) free version (suffix, ?t) , with a 100% matte tin plated leadframe. description (continued) 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 12 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 i outs(lim) ? ? 50 ma response characteristics power-on state pos t < t response ? high ? v power-on time 2,6 t po v cc > v cc(min) ? 4.5 9 ms settling time 3,6 t settling f bdiff 100 hz 0 ? 50 ms response time 6 t response equal to t po + t settling ; 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 4 t r r pu = 1 k , c outc2 = 10 pf ? ? 200 ns output fall time t f r pu = 1 k , i sink = 20 ma, c outc2 = 10 pf ? ? 200 ns continued on next page.
high precision hall effect ac-coupled differential sensor ic with integrated filter capacitor A1421, a1422, and a1423 4 allegro microsystems, inc. 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com operating characteristics, continued 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 magnetic characteristics 5,6 operate point b op 1421, b diff increasing, f bdiff = 200 hz, b diff = 50 gp-p v out switches from low (on) to high (off) 0.0 15.0 27.5 g 1422, b diff increasing, f bdiff = 200 hz, b diff = 50 gp-p v out switches from high (off) to low (on) 5.0 15.0 35.0 g 1423, b diff increasing, f bdiff = 200 hz, b diff = 200 gp-p v out switches from high (off) to low (on) 10.0 65.0 100.0 g release point b rp 1421, b diff decreasing, f bdiff = 200 hz, b diff = 50 gp-p v out switches from high (off) to low (on) ?12.5 0.0 7.5 g 1422, b diff decreasing, f bdiff = 200 hz, b diff = 50 gp-p v out switches from low (on) to high (off) ?35.0 ?15.0 ?5.0 g 1423, b diff decreasing, f bdiff = 200 hz, b diff = 200 gp-p v out switches from low (on) to high (off) ?100 ?65.0 ?10.0 g hysteresis b hys 1421, f bdiff = 200 hz, b diff = 50 gp-p 5 15 35 g 1422, f bdiff = 200 hz, b diff = 50 gp-p ? 30 ? g 1423, f bdiff = 200 hz, b diff = 200 gp-p ? 130 ? g applied magnetic field 7 b diff differential p-p magnetic field ? ? 1250 g 1 i cc is equivalent to i cc(max) + 3 ma. 2 time required to initialize device. 3 time required for the output switchpoints to be within speci cation. 4 output rise time will be dominated by the rc time constant. 5 for lower frequencies, the absolute values of b op , b rp , and b hys may decrease due to delay induced by the high-pass lter. 6 see de nitions of terms section. 7 exceeding the maximum magnetic eld may result in compromised absolute accuracy.
high precision hall effect ac-coupled differential sensor ic with integrated filter capacitor A1421, a1422, and a1423 5 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 minimum-k pcb (single-sided with copper limited to solder pads) 177 oc/w *in still air. additional thermal information available on allegro web site. 20 40 60 80 100 120 140 160 180 maximum allowable v cc (v) 8 10 12 14 0 2 4 6 16 18 20 22 24 26 28 30 (r q ja = 177 oc/w) minimum-k pcb v cc(min) v cc(max) 20 40 60 80 100 120 140 160 180 temperature (c) power dissipation, p d (mw) (r q ja = 177 oc/w) minimum-k pcb 0 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 800 850 900 the following provide additional information about some of the parameters cited. for additional information, visit the allegro web site at www.allegromicro.com . applied magnetic field, b diff ? the differential magnetic flux density, which is calculated as the arithmetic difference of the flux densities observed by each of the two hall elements. f bdiff is the input signal frequency. output off switchpoint (operate point), b op ? the value of increasing differential magnetic flux density at which the device output switches from low to high (A1421) or high to low (a1422 and a1423). output on switchpoint (release point), b rp ? the value of decreasing differential magnetic flux density at which the device output switches from high to low (A1421) or from low to high (a1422 and a1423). 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 settling ? 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. supply current (on), i cc(on) ? the current draw of the device with the output transitor is turned on. supply current (off), i cc(off) ? the current draw of the device with the output transitor is turned off. response time, t response ? the total time required for generating zero-crossing output transitions after initialization (the sum of power-on time and settling time). de nitions of terms power derating curve t j(max) = 165c; i cc = i cc(max) maximum power dissipation t j(max) = 165c; i cc = i cc(max) ; v cc = v cc(max)
high precision hall effect ac-coupled differential sensor ic with integrated filter capacitor A1421, a1422, and a1423 6 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) 4.5 20.0 12.0 v cc (v) 150 ?40 25 t a (oc) 150 ?40 25 t a (oc) 150 ?40 25 t a (oc) i cc(off) by t a ambient temperature, t a (oc) current (ma) 10.0 9.0 8.0 7.0 6.0 5.0 4.0 3.0 2.0 1.0 0.0 ?50 0 50 100 150 200 over v cc range i cc(off) by v cc supply voltage, v cc (v) current (ma) 10.0 9.0 8.0 7.0 6.0 5.0 4.0 3.0 2.0 1.0 0.0 0 5 10 15 20 25 over t a range i cc(on) by v cc supply voltage, v cc (v) current (ma) 10.0 9.0 8.0 7.0 6.0 5.0 4.0 3.0 2.0 1.0 0.0 0 5 10 15 20 25 over t a range supply voltage, v cc (v) 0 5 10 15 20 25 i cc(on) by t a ambient temperature, t a (oc) current (ma) 10.0 9.0 8.0 7.0 6.0 5.0 4.0 3.0 2.0 1.0 0.0 ?50 0 50 100 150 200 over v cc range v out(sat) by t a ambient temperature, t a (oc) voltage (mv) 500 450 400 350 300 250 200 150 100 50 0 ?50 0 50 100 150 200 over v cc range; i sink = 20 ma v out(sat) by v cc voltage (mv) 500 450 400 350 300 250 200 150 100 50 0 over t a range; i sink = 20 ma continued on next page .
high precision hall effect ac-coupled differential sensor ic with integrated filter capacitor A1421, a1422, and a1423 7 allegro microsystems, inc. 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com simulation results continued on next page .
high precision hall effect ac-coupled differential sensor ic with integrated filter capacitor A1421, a1422, and a1423 8 allegro microsystems, inc. 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com simulation results, continued continued on next page .
high precision hall effect ac-coupled differential sensor ic with integrated filter capacitor A1421, a1422, and a1423 9 allegro microsystems, inc. 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com simulation results, continued continued on next page .
high precision hall effect ac-coupled differential sensor ic with integrated filter capacitor A1421, a1422, and a1423 10 allegro microsystems, inc. 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com simulation results, continued
high precision hall effect ac-coupled differential sensor ic with integrated filter capacitor A1421, a1422, and a1423 11 allegro microsystems, inc. 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com 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 test is done with no external components. please contact allegro microsystems for emc performance information. v s c1 r2 1 vcc 3 test vout gnd 2 4 r1 c2 A1421, a1422 or a1423 component value units r1 * 1k r2 100 c1 0.1 f c2 0.1 f * pull-up resistor not required for protection but for normal operation. recommended emc test circuit. test circuit recommended configuration may change after evaluation of first silicon.
high precision hall effect ac-coupled differential sensor ic with integrated filter capacitor A1421, a1422, and a1423 12 allegro microsystems, inc. 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com applications information the A1421, a1422, and a1423 are versatile high-precision dif- ferential sensor ics that can be used in a wide range of applica- tions. proper choice of the target material and shape, magnet material and shape, and assembly techniques enables large working air gaps and high switchpoint accuracy over the device operating temperature range. device operation the device ic contains two integrated hall transducers that are used to differentially respond to a magnetic field across the sur- face of the ic. referring to figure 1, which shows curves for the A1421 as an example, the trigger switches the output when the differential magnetic field crosses the b op level while increasing in strength (referred to as the positive direction). in the example, the A1421 output voltage switches high (off), and switches the output low (on) when the differential magnetic field crosses b rp while decreasing (the negative direction). the operation is achieved through the use of two separate com- parators. one comparator has a positive hysteresis, b hys1 , and the other a negative hysteresis, b hys2 . therefore, one comparator switches at the b op crossing on an increasing differential signal and the other switches at the b rp crossing on a decreasing differ- ential signal. the hysteresis on each comparator precludes false switching on noise or target jitter. the behavior is similar for the a1422 and the a1423. the switchpoints are as shown in the magnetic charactersitics table, and the output polarity is inverted. this is illustrated in figure 2, on the next page. start-up during power-on time, t po , the output signal, v out , is high. beyond this time, if the applied magnetic field, b diff , is smaller than b hys , the switching state and v out polarity are indeter- minate. v out will be valid for b diff > b hys , after the additional settling time, t settling , has also elapsed. delay the bandpass filter induces delay in the output signal, v out , rel- ative to the applied magnetic field, b diff . simulation data shown figure 1. typical output characteristics with dual comparator operation. the example shown is for the A1421. characteristics shown without delay, see characteristic data charts for delay and phase shift contributions. on off off b rp(typ)1421 b op(typ)1421 1421 output signal, v out 1421 switching state applied magnetic field, b diff comparator 1, A1421 comparator 2, A1421 b hys2 ? b hys1 ? 0.0 15.0
high precision hall effect ac-coupled differential sensor ic with integrated filter capacitor A1421, a1422, and a1423 13 allegro microsystems, inc. 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com on off b rp(typ)1421 and output signal, v out 1421 switching state applied magnetic field, b diff b 0.0 15.0 C15.0 op(typ)1421, 1422 off off on on and output signal, v out 1422 switching state off on on and output signal, v out 1423 switching state t+ b op(typ)1423 b rp(typ)1422 b rp(typ)1423 65.0 C65.0 figure 2. comparative typical output characteristics. this chart illustrates the switchpoints and the output polarities of the A1421, a1422, and the a 1423. characteristics shown without delay, see characteristic data charts for delay and phase shift contributi ons. in the characteristic data section quantify the effect of the input signal amplitude on the phase shift of the output. positive values of delay indicate a lagging output, while negative values indicate a leading output. ac-coupled operation steady-state magnet and system offsets are eliminated using an on-chip differential bandpass filter. the upper and lower cut-off frequencies of this patented filter are set using an internal inte- grated capacitor. the differential structure of this filter improves the ability of the ic to reject single-ended noise on the gnd or vcc lines and, as a result, makes the device more resistant to emi (electromagnetic interference) typically seen in hostile remote-sensing environments. power supply protection the device contains an on-chip voltage regulator and can operate over a wide supply voltage range. in applications that operate the device from an unregulated power supply, transient protection must be added externally. for applications using a regulated line, emi/rfi protection may still be required. the circuit shown in figure 3 is the most basic configuration required for proper device operation. typical circuit a pull-up resistor, r pu , is required between the supply and out- put terminals, as shown in figure 3. also, the auxilliary terminal, test, must be connected externally to the gnd terminal. 2 1 3 4 v out 0.1 uf r pu v s vcc test vout gnd A1421, a1422 or a1423 figure 3. basic application circuit . a pull-up resistor, r pu , is required with the output driver.
high precision hall effect ac-coupled differential sensor ic with integrated filter capacitor A1421, a1422, and a1423 14 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 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, r ? ja , 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 ? jc , is relatively small component of r ? ja . ambient air temperature, t a , and air motion are significant 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 = 12 v, i cc = 4.2 ma, and r ? ja = 177 c/w, then: p d = v cc i cc = 12 v 4.2 ma = 50 mw ?? t = p d r ? ja = 50 mw 177 c/w = 9c t j = t a + ? t = 25c + 9c = 34c 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, package l-i1, using minimum- k pcb observe the worst-case ratings for the device, specifically: 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 = 91 mw finally, invert equation 1 with respect to voltage: v cc(est) = p d(max) i cc(max) = 91 mw 7.0 ma = 13 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.
high precision hall effect ac-coupled differential sensor ic with integrated filter capacitor A1421, a1422, and a1423 15 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 ?2004-2009, 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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