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description the a1642 is an optimized hall effect sensing integrated circuit that provides a user-friendly solution for true zero-speed digital ring-magnet sensing in two-wire applications. this small package can be easily assembled and used in conjunction with a wide variety of target shapes and sizes. the integrated circuit incorporates dual hall effect elements and signal processing that switches in response to differential magnetic signals created by ring magnet poles. the circuitry contains a sophisticated digital circuit to reduce system offsets, to calibrate the gain for air-gap?independent switchpoints, and to achieve true zero-speed operation. signal optimization occurs at power-on through the combination of offset and gain adjust and is maintained throughout the operating time with the use of a running-mode calibration. the running-mode calibration allows immunity to environmental effects such as micro-oscillations of the target or sudden air gap changes. the regulated current output is configured for two-wire applications and the a1642 is ideally suited for obtaining speed and duty cycle information in abs (antilock braking systems). the 1.5 mm spacing between the dual hall elements is optimized for fine pitch ring-magnet?based configurations. for applications requiring sensing of rotating ferrous gears and targets, refer to the allegro ats series of products. the package is lead (pb) free, with 100% matte tin leadframe plating. a1642lkn-ds, rev. 4 features and benefits ? running mode calibration for continuous optimization ? single chip ic for high reliability ? internal current regulator for 2-wire operation ? precise duty cycle signal over operating temperature range ? large operating air gaps ? automatic gain control (agc) for air gap independent switchpoints ? automatic offset adjustment (aoa) for signal processing optimization ? true zero-speed operation ? undervoltage lockout ? wide operating voltage range ? wide-lead package suitable for welding external components directly to the package leads or for welding the device to a leadframe. two-wire true zero-speed miniature differential peak-detecting sensor ic with continuous calibration package: 4-pin sip (suffix kn) functional block diagram not to scale a1642 vcc automatic offset control aoa dac hall amplifier agc dac gain tracking dac peak hold gain control internal regulator test signals gnd test
two-wire true zero-speed miniature differential peak-detecting sensor ic with continuous calibration a1642 2 allegro microsystems, llc 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com 1234 pin-out diagram absolute maximum ratings characteristic symbol notes rating units supply voltage v cc 28 v reverse supply voltage v rcc ?18 v 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 function 1 vcc connects power supply to chip 2 nc no connection 3 test float or tie to gnd 4 gnd ground connection selection guide part number i cc range packing* A1642LKNTN-I1-T 4.0 ma low to 16.0 ma high tape and reel, 13-inch reel 4000 pieces per reel a1642lkntn-i2-t 5.9 ma low to 16.8 ma high a1642lkntn-i3-t 5.9 ma low to 16.0 ma high *contact allegro for additional packing options
two-wire true zero-speed miniature differential peak-detecting sensor ic with continuous calibration a1642 3 allegro microsystems, llc 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com operating characteristics t a and v cc within speci cation, unless otherwise noted characteristic symbol test conditions min. typ. 1 max. units electrical characteristics supply voltage 2 v cc operating; t j < 165c 4.0 ? 24 v undervoltage lockout v cc(uv) v cc 0 5 v and 5 0 v ? ? 4.0 v supply zener clamp voltage v z i cc = i cc(max) + 3 ma; t a = 25c 28 ? ? v supply zener current i z test conditions only; v z = 28 v ? ? i cc(max) + 3 ma ma supply current i cc(low) a1642lkn-i1 4.0 6.0 8.0 ma a1642lkn-i2, a1642lkn-i3 5.9 7.0 8.4 ma i cc(high) a1642lkn-i1, a1642lkn-i3 12.0 14.0 16.0 ma a1642lkn-i2 11.8 14.0 16.8 ma supply current ratio i cc(high) / i cc(low) ratio of high current to low current 1.85 ? 3.05 ? reverse battery current i rcc v rcc = ?18 v ? ? ?5 ma power-on state characteristics power-on state 3 pos t > t po ?i cc(high) ?? power-on time 4 t po f op < 100 hz ? 1 2 ms output stage output slew rate 5 di/dt r load = 100 , c load = 10 pf ? 14 ? ma/ s continued on the next page.
two-wire true zero-speed miniature differential peak-detecting sensor ic with continuous calibration a1642 4 allegro microsystems, llc 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com operating characteristics (continued) t a and v cc within speci cation, unless otherwise noted characteristic symbol test conditions min. typ. 1 max. units switchpoint characteristics operating speed f op 0 ? 8,000 hz analog signal bandwidth bw equivalent to f ? 3 db 20 40 ? khz operate point b op transitioning from i cc(high) to i cc(low) ; positive peak referenced; ag < ag max ? 120 ? mv release point b rp transitioning from i cc(low) to i cc(high) ; negative peak referenced; ag < ag max ? 120 ? mv calibration initial calibration c i quantity of rising output (current) edges required for accurate edge detection ? ? 3 edge dac characteristics allowable user-induced differential offset operating within speci cation ? ? 90 g functional characteristics 6 operating signal range 7 sig operating within speci cation 30 ? 1000 g minimum operating signal sig op(min) output switching (no missed edges); ? dc not guaranteed 20 ? ? g 1 typical values are at t a = 25c and v cc = 12 v. performance may vary for individual units, within the speci ed maximum and minimum limits. 2 maximum voltage must be adjusted for power dissipation and junction temperature; see power derating section. 3 please refer to device operation section. 4 power-on time includes the time required to complete the internal automatic offset adjust. the dac is then ready for peak acqui sition. 5 di is the difference between 10% of i cc(low) and 90% of i cc(high) , and dt is the time period between those two points. note: di/dt is dependent upon the value of the bypass capacitor, if one is used. 6 functional characteristics valid only if magnetic offset is within the speci ed range for allowable user induced differential offset. 7 in order to remain in speci cation, the magnetic gradient must induce an operating signal greater than the minimum value speci ed. this includes the effect of target wobble.
two-wire true zero-speed miniature differential peak-detecting sensor ic with continuous calibration a1642 5 allegro microsystems, llc 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com characteristic data supply current (high) versus ambient temperature (i1 trim) 12 13 14 15 16 -50 0 50 100 150 t a (c) i cc(high) (ma) v cc (v) 24 12 4 supply current (high) versus supply voltage (i1 trim) 12 13 14 15 16 0 5 10 15 20 25 v cc (v) i cc(high) (ma) t a (c) -40 25 85 150 supply current (low) versus ambient temperature (i1 trim) 4 5 6 7 8 -50 0 50 100 150 t a (c) i cc(low) (ma) v cc (v) 24 12 4 supply current (low) versus supply voltage (i1 trim) 4 5 6 7 8 0 5 10 15 20 25 v cc (v) i cc(low) (ma) t a (c) -40 25 150
two-wire true zero-speed miniature differential peak-detecting sensor ic with continuous calibration a1642 6 allegro microsystems, llc 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com teag in (mm) teag out (mm) allowable air gap movement from teag cal * -0.2 0 0.2 0.4 0.6 0.8 1.0 1.2 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 characteristic allowable air gap movement the colored area in the chart above shows the region of allow- able air gap movement within which the device will continue output switching. the output duty cycle is wholly dependent on the target?s magnetic signature across the air gap range of move- ment, and may not always be within speci cation throughout the entire operating region (to ag (opmax) ). the axis parameters for the chart are de ned in the drawings below. as an example, assume the case where the air gap is allowed to vary from the nominal installed air gap (teag cal , panel a) within the range de ned by an increase of ? teag out = 0.35 mm (shown in panel b), and a decrease of ? teag in = 0.65 mm (shown in panel c). this case is plotted with an ? x ? in the chart above. teag in a1642 a1642 teag out (a) a1642 teag cal (b) (c) *data based on study performed using spur gear reference target 60-0, and applicable to ring magnet targets with similar magnetic characteristics.
two-wire true zero-speed miniature differential peak-detecting sensor ic with continuous calibration a1642 7 allegro microsystems, llc 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 single-layer pcb with copper limited to solder pads 170 oc/w *additional information is available on the allegro web site. 1300 1200 1100 1000 900 800 700 600 500 400 300 200 100 0 power dissipation versus ambient temperature (r q ja = 170 oc/w) 20 40 60 80 100 120 140 160 180 ambient temperature, t a (c) power dissipation, p d (m w) 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 ambient temperature, t a (oc) maximum allowable v cc (v) power derating curve (r q ja = 170 oc/w) v cc(min) v cc(max)
two-wire true zero-speed miniature differential peak-detecting sensor ic with continuous calibration a1642 8 allegro microsystems, llc 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com sensing technology the single-chip differential hall effect sensor ic possesses two hall elements, which sense the magnetic pro le of the ring mag- net simultaneously, but at different points (spaced at a 1.5 mm pitch), generating a differential internal analog voltage, v proc , that is processed for precise switching of the digital output signal. the hall ic is self-calibrating and also possesses a temperature compensated ampli er and offset compensation circuitry. its voltage regulator provides supply noise rejection throughout the operating voltage range. changes in temperature do not greatly affect this device due to the stable ampli er design and the offset compensation circuitry. the hall transducers and signal process- ing electronics are integrated on the same silicon substrate, using a proprietary bicmos process. target profiling an operating device is capable of providing digital informa- tion that is representative of the magnetic features on a rotating target. the waveform diagram shown in gure 3 presents the automatic translation of the magnetic pro le to the digital output signal of the device. output polarity figure 3 shows the output polarity for the orientation of target and device shown in gure 2. the target direction of rota- tion shown is: perpendicular to the leads, across the face of the device, from the pin 1 side to the pin 4 side. this results in the device output switching from high, i cc(high) , to low i cc(low) , as the leading edge of a north magnetic pole passes the device face. in this con guration, the device output current switches to its low polarity when a north pole is the target feature nearest to the device. if the direction of rotation is reversed, then the output polarity inverts. note that output voltage polarity is dependent on the position of the sense resistor, r sense (see gure 4). target (ring magnet) (pin 1 side) (pin 4 side) hall ic element pitch hall element 1 hall element 2 n n s s of device rotating target branded face 1 4 functional description figure 1. relative motion of the target is detected by the dual hall ele- ments mounted on the hall ic. figure 2. this left-to-right (pin 1 to pin 4) direction of target rotation results in a low output signal when a magnetic north pole of the target is nearest the face of the device (see gure 3). a right-to-left (pin 4 to pin 1) rotation inverts the output signal polarity. figure 4: voltage pro les for high side and low side two-wire sensing. figure 3. output pro le of a ring magnet target for the polarity indicated in gure 2. a1642 vcc gnd v cc i cc 1 4 v out(l) a1642 vcc gnd v supply 1 4 v out(h) i cc r sense r sense i out v out(h) v+ v out(l) v+ i+ n n s s representative differential magnetic profile target ring magnet device electrical output profile, i out
two-wire true zero-speed miniature differential peak-detecting sensor ic with continuous calibration a1642 9 allegro microsystems, llc 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com automatic gain control (agc) this feature allows the device to operate with an optimal internal electrical signal, regardless of the air gap (within the ag speci- cation). during calibration, the device determines the peak-to- peak amplitude of the signal generated by the target. the gain of the device is then automatically adjusted. figure 5 illustrates the effect of this feature. automatic offset adjust (aoa) the aoa is patented circuitry that automatically compensates for the effects of chip, magnet, and installation offsets. (for capability, see dynamic offset cancellation, in the operat- ing characteristics table.) this circuitry is continuously active, including both during calibration mode and running mode, compensating for offset drift. continuous operation also allows it to compensate for offsets induced by temperature variations over time. digital peak detection a digital dac tracks the internal analog voltage signal v proc , and is used for holding the peak value of the internal analog signal. in the example shown in gure 6, the dac would rst track up with the signal and hold the upper peak?s value. when v proc drops below this peak value by b op , the device hyster- esis, the output would switch and the dac would begin tracking the signal downward toward the negative v proc peak. once the dac acquires the negative peak, the output will again switch states when v proc is greater than the peak by the value b rp . at this point, the dac tracks up again and the cycle repeats. the digital tracking of the differential analog signal allows the device to achieve true zero-speed operation. figure 5. automatic gain control (agc). the agc function corrects for variances in the air gap. differences in the air gap affect the magnetic gradient, but agc prevents that from affecting device performance, as shown in the lowest panel. n n s s ag small ag large ag small ag large internal differential analog signal response, with agc internal differential analog signal response, without agc v+ v+ target ring magnet figure 6: peak detecting switchpoint detail device output current b rp internal differential analog signal v+ i+ b op
two-wire true zero-speed miniature differential peak-detecting sensor ic with continuous calibration a1642 10 allegro microsystems, llc 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com power supply protection the device contains an on-chip regulator and can operate over a wide v cc range. for devices that need to operate from an unregulated power supply, transient protection must be added externally. for applications using a regulated line, emi/rfi pro- tection may still be required. contact allegro microsystems for information on the circuitry needed for compliance with various emc speci cations. refer to gure 7 for an example of a basic application circuit. undervoltage lockout when the supply voltage falls below the undervoltage lockout voltage, v cc(uv) , the device enters reset, where the output state returns to the power-on state (pos) until suf cient v cc is sup- plied. i cc levels may not meet datasheet limits when v cc < v cc(min) . assembly description this device is integrally molded into a plastic body that has been optimized for size, ease of assembly, and manufacturability. high operating temperature materials are used in all aspects of construction. diagnostics the regulated current output is con gured for two wire appli- cations, requiring one less wire for operation than do switches with the more traditional open-collector output. additionally, the system designer inherently gains diagnostics because there is always output current flowing, which should be in either of two narrow ranges, shown in figure 8 as i cc(high) and i cc(low) . any current level not within these ranges indicates a fault condi- tion. if i cc > i cc(high)max , then a short condition exists, and if i cc < i cc(low)min , then an open condition exists. any value of i cc between the allowed ranges for i cc(high) and i cc(low) indicates a general fault condition. figure 7: typical application circuit a1642 vcc gnd v+ 0.01 1 4 f ecu pins 2 and 3 floating r 100 sense c byp figure 8: diagnostic characteristics of supply current values i cc(high)max i cc(high)min range for valid i cc(high) range for valid i cc(low) i cc(low)max i cc(low)min 0 +ma ? ? short fault open
two-wire true zero-speed miniature differential peak-detecting sensor ic with continuous calibration a1642 11 allegro microsystems, llc 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com device operation each operating mode is described in detail below. power-on when power (v cc > v cc(min) ) is applied to the device, a short period of time is required to power the various portions of the ic. during this period, the a1642 powers-on in the high current state, i cc(high) . after power-on, there are conditions that could induce a change in the output state. such an event could be caused by thermal transients, but would require a static applied magnetic eld, proper signal polarity, and particular direction and magnitude of internal signal drift. initial offset adjust the device initially cancels the effects of chip, magnet, and installation offsets. once offsets have been cancelled, the digital tracking dac is ready to track the signal and provide output switching. the period of time required for both power-on and initial offset adjust is de ned as the power-on time. calibration mode the calibration mode allows the device to automatically select the proper signal gain and continue to adjust for offsets. the agc is active, and selects the optimal signal gain based on the amplitude of the v proc signal. following each adjustment to the agc dac, the offset dac is also adjusted to ensure the internal analog signal is properly centered. during this mode, the tracking dac is active and output switch- ing occurs, but the duty cycle is not guaranteed to be within speci cation. running mode after the initial calibration period, c i , establishes a signal gain, the device moves to running mode. during running mode, the device tracks the input signal and gives an output edge for every peak of the signal. aoa remains active to compensate for any offset drift over time. the a1642 incorporates a novel algorithm for adjusting the signal gain during running mode. this algorithm is designed to optimize the v proc signal amplitude in instances where the magnetic signal ?seen? during the calibration period is not repre- sentative of the amplitude of the magnetic signal for the installed device air gap (see gure 9). device electrical output, i out internal differential signal, v proc b rp b op b op b rp 1 2 3 4 5 figure 9: operation of running mode gain adjust. position 1. the device is initially powered-on. self-calibration occurs. position 2. small amplitude oscillation of the target sends an erroneously small differential signal to the device. the ampli- tude of v proc is greater than the switching hysteresis (b op and b rp ), and the device output switches. position 3. the calibration period completes on the third rising output edge, and the device enters running mode. position 4. true target rotation occurs and the correct magnetic signal is generated for the installation air gap. the estab- lished signal gain is too large for the target?s rotational magnetic signal at the given air gap. position 5. running mode calibration corrects the signal gain to an optimal level for the installation air gap.
two-wire true zero-speed miniature differential peak-detecting sensor ic with continuous calibration a1642 12 allegro microsystems, llc 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com power derating example : reliability for v cc at t a = 150c, package kn (i1 trim), using 1-layer pcb observe the worst-case ratings for the device, speci cally: r ? ja = 170 c/w, t j (max) = 165c, v cc (max) = 24 v, and i cc (max) = 16 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 170 c/w = 88.2 mw finally, invert equation 1 with respect to voltage: v cc(est) = p d (max) i cc (max) = 88.2 mw 16 ma = 5.5 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. 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 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 = 12 v, i cc = 6 ma, and r ? ja = 170 c/w, then: p d = v cc i cc = 12 v 6 ma = 72 mw ?? t = p d r ? ja = 72 mw 170 c/w = 12.2c t j = t a + ? t = 25c + 12.2c = 37.2c 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 .
two-wire true zero-speed miniature differential peak-detecting sensor ic with continuous calibration a1642 13 allegro microsystems, llc 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com package kn, 4-pin sip 24 3 1 1.27 nom 3.19 nom 8.12 ref 0.38 ref 2.16 max 6.00 ref 45 45 a 0.84 ref b b c c gate and tie bar burr area dambar removal protrusion (8x) a for reference only; not for tooling use (reference dwg-9015) 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 1.03 +0.08 ?0.05 0.41 +0.07 ?0.05 14.74 0.51 1.55 0.05 branding scale and appearance at supplier discretion e1 e2 1.85 1.32 1.50 d d active area depth 0.43 mm ref hall elements (e1,e2), not to scale e e e e
two-wire true zero-speed miniature differential peak-detecting sensor ic with continuous calibration a1642 14 allegro microsystems, llc 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com copyright ?2005-2013, allegro microsystems, llc allegro microsystems, llc reserves the right to make, from time to time, such de par tures from the detail spec i fi ca tions a s may be required to permit 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, llc assumes n o 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. 4 january 16, 2012 update product variants offered

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