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description the components in speed sensing applications continue to diminish in size to meet spatial constraints and weight reduction requirements. as the geometries of gears become smaller, this can compromise the capabilities of a gear speed sensor. the ats645 hall-element-to-hall-element spacing of only 1.5 mm makes this device uniquely capable of accommodating very fine-pitch gears. in addition, the ats645 signal peak-detecting algorithm supports consistent switching at relatively large air gaps, where the peak-to-peak amplitude is small. these features make the ats645 the ideal solution to detect the speed of fine- pitch targets such as those found in abs (antilock braking) systems. the ats645 combines a hall-effect sensing integrated circuit and magnet to provide a manufacturer-friendly solution for true zero-speed digital gear-tooth sensing in two-wire applications. the device consists of a single-shot molded plastic package that includes a samarium cobalt magnet, a pole piece, and a hall-effect integrated circuit that has been optimized to the magnetic circuit. this small package can be easily assembled and used in conjunction with a wide variety of gear shapes and sizes. ats645-ds, rev. 3 features and benefits ? fully optimized differential digital gear tooth sensor ? single chip ic for high reliability ? internal current regulator for 2-wire operation ? small mechanical size (8 mm diameter x 5.5 mm depth) ? air gap independent switchpoints ? digital output representing gear profile ? precise duty cycle signal over operating temperature range ? large operating air gaps ? automatic gain control (agc) two-wire true zero speed miniature differential peak-detecting gear tooth sensor continued on the next page? functional block diagram not to scale packages: 4 pin sip (suffix sh) ats645lsh continued on the next page? vcc automatic offset control aoa dac hall amplifier agc dac gain tracking dac peak hold internal regulator test signals gnd test
true zero speed miniature differential peak- detecting gear tooth sensor ats645lsh 2 allegro microsystems, inc. 115 northeast cutoff, box 15036 worcester, massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com ? automatic offset adjustment (aoa) ? true zero-speed operation ? undervoltage lockout ? wide operating voltage range ? defined power-on state the integrated circuit incorporates a dual-element hall effect sensor as well as signal processing that switches the output state in response to changes in the magnetic gradients created by ferrous gear teeth. the circuitry contains a sophisticated digital circuit to eliminate magnet and system offsets and to achieve true zero speed operation (u.s. patent 5,917,320). a-d and d-a converters are used to adjust the device gain at power-on and to allow switching independent of the breadth of the air gap. the regulated current output is configured for two wire applications, requiring one less wire for operation than do switches with the more traditional open-collector output.the package is available in a lead (pb) free version, with 100% matte tin leadframe plating. part number pb-free 1 packing 2 i cc typical ats645lshtn-i1-t yes tape and reel 13-in. 800 pcs./reel 6.0 low to 14.0 high ma ATS645LSHTN-I2-T yes tape and reel 13-in. 800 pcs./reel 7.0 low to 14.0 high ma 1 pb-based variants are being phased out of the product line. a. certain variants cited in this footnote are in production but have been determined to be last time buy. this classification indicates that sale of this device is currently restricted to existing customer applications. the device should not be purchased for new design app lications because obsolescence in the near future is probable. samples are no longer available. status change: october 31, 2006. deadline for rec eipt of last time buy orders: april 27, 2007. these variants include: ats645lshtn-i1. b. certain variants cited in this footnote are in production but have been determined to be not for new design. this classification indicates that sale of this device is currently restricted to existing customer applications. the device should not be purchased for new design applications because obsolescence in the near future is probable. samples are no longer available. status change: may 1, 2006. these variants include: ats645lshtn-i2. 2 contact allegro for additional packing options. 3 some restrictions may apply to certain types of sales. contact allegro for details. features and benefits (continued) description (continued) absolute maximum ratings characteristic symbol notes rating units supply voltage v cc 28 ? 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 name description number vcc connects power supply to chip 1 nc no connection 2 test for allegro use, oat or tie to gnd 3 gnd ground terminal 4 2 4 3 1 pin-out diagram
true zero speed miniature differential peak- detecting gear tooth sensor ats645lsh 3 allegro microsystems, inc. 115 northeast cutoff, box 15036 worcester, massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com operating characteristics using reference target 60-0, 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 < 165 c 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) ats645lsh-i1 4.0 6 8.0 ma ats645lsh-i2 5.9 7 8.4 ma i cc(high) ats645lsh-i1 12.0 14.0 16.0 ma ats645lsh-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 ? power-on state characteristics power-on state pos t > t po ?i cc(high) ?? power-on time 3 t po target gear speed < 100 rpm ? 1 2 ms output stage output slew rate 4 di/dt r load = 100 , c load = 10 pf ? 10 ? ma/ s continued on the next page.
true zero speed miniature differential peak- detecting gear tooth sensor ats645lsh 4 allegro microsystems, inc. 115 northeast cutoff, box 15036 worcester, massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com operating characteristics (continued) using reference target 60-0, t a and v cc within speci cation, unless otherwise noted characteristic symbol test conditions min. typ. 1 max. units switchpoint characteristics rotation speed s rot reference target 60-0 0 ? 8,000 rpm analog signal bandwidth bw equivalent to f ? 3db 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 output switching only; may not meet datasheet speci- cations ?60 ? 60 g functional characteristics 5 operational air gap range 6 ag ? dc within speci cation 0.5 ? 2.75 mm maximum operational air gap range ag op(max) output switching (no missed edges); ? dc not guaranteed ??3mm duty cycle variation 7 ? dc wobble < 0.5mm; typical value at ag = 1.5 mm, for max., min., ag within speci cation 43 53 63 % operating magnetic flux density differential 8 b ag(p-p) 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 power-on time includes the time required to complete the internal automatic offset adjust. the dacs are then ready for peak acq uisition. 4 di is the difference between 10% of i cc(low) and 90% of i cc(high) , and dt is time period between those two points. note: di/dt is dependent upon the value of the bypass capacitor, if one is used. 5 functional characteristics valid only if magnetic offset is within the speci ed range for allowable user induced differential offset. 6 ag is dependent on the available magnetic eld. the available eld is dependent on target geometry and material, and should be independently characterized. the eld available from the reference target is given in the reference target parameter section of the datasheet. 7 duty cycle speci cation may not be met if the magnetic signal during the calibration period is not representative of the installation air gap. 8 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.
true zero speed miniature differential peak- detecting gear tooth sensor ats645lsh 5 allegro microsystems, inc. 115 northeast cutoff, box 15036 worcester, massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com reference target, 60-0 (60 tooth target) characteristics symbol test conditions typ. units symbol key outside diameter d o outside diameter of target 120 mm face width f breadth of tooth, with respect to sensor 6mm circular tooth length t length of tooth, with respect to sensor; measured at d o 3mm circular valley length t v length of valley, with respect to sensor; measured at d o 3mm tooth whole depth h t 3mm material low carbon steel ? ? reference gear magnetic gradient amplitude with reference to air gap air gap (mm) peak-to-peak differential b (g) 0 100 200 300 400 500 600 700 800 11.52 0.5 2.5 3 reference gear magnetic profile two tooth-to-valley transitions -500 -400 -300 -200 -100 0 100 200 300 400 500 gear rotation () differential b* (g) 024681012 0.50 (mm) air gap 0.50 mm ag 3.00 mm ag 0.75 1.00 1.25 1.50 1.75 2.00 2.25 2.50 2.75 3.00 reference target 60-0 of sensor branded face *differential b corresponds to the calculated difference in the magnetic eld as sensed simultaneously at the two hall elements in the device (b diff = b e1 ? b e2 ).
true zero speed miniature differential peak- detecting gear tooth sensor ats645lsh 6 allegro microsystems, inc. 115 northeast cutoff, box 15036 worcester, massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com characteristic data i1 trim duty cycle vs. air gap 100 rpm, v cc = 12 v 35 40 45 50 55 60 65 0 0.5 1 1.5 2 2.5 3 3.5 air gap (mm) duty cycle (%) duty cycle vs. air gap 1000 rpm, v cc = 12 v 35 40 45 50 55 60 65 0 0.5 1 1.5 2 2.5 3 3.5 air gap (mm) duty cycle (%) duty cycle vs. target speed air gap 1.5 mm, v cc = 12 v 35 40 45 50 55 60 65 0 200 400 600 800 1000 1200 1400 1600 target speed (rpm) duty cycle (%) supply current vs. supply voltage 0 3 6 9 12 15 18 0 5 10 15 20 25 30 v cc (v) i cc (ma) i cc(high) i cc(low) t a , (oc) -40 25 150 t a , (oc) -40 25 150 t a , (oc) -40 25 150 t a , (oc) -40 25 150
true zero speed miniature differential peak- detecting gear tooth sensor ats645lsh 7 allegro microsystems, inc. 115 northeast cutoff, box 15036 worcester, massachusetts 01615-0036 (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 126 oc/w two-layer pcb with 3.8 in. 2 of copper area on each side con- nected with thermal vias and to device ground pin 84 oc/w *additional information is available on the allegro web site. 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) t j(max) = 165oc; i cc =i cc(max) power derating curve (r ja = 126 oc/w) (r ja = 84 oc/w) 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) t j(max) =165oc;v cc =v cc(max) ;i cc =i cc(max) maximum power dissipation, p d(max) (r ja = 126 oc/ w ) ( r ja = 84 oc/w )
true zero speed miniature differential peak- detecting gear tooth sensor ats645lsh 8 allegro microsystems, inc. 115 northeast cutoff, box 15036 worcester, massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com sensing technology the gear tooth sensor subassembly contains a single-chip dif- ferential hall effect sensor ic, an optimized samarium cobalt magnet, and a at ferrous pole piece. the hall ic supports two hall elements, which sense the magnetic pro le of the ferrous target 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 tempera- ture compensated ampli er and offset cancellation 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 rejection circuitry. the hall transducers and signal processing electronics are integrated on the same silicon substrate, using a proprietary bicmos process. target profiling an operating device is capable of providing digital information that is representative of the mechanical features on a rotating tar- get. the waveform diagram shown in gure 3 presents the auto- matic translation of the mechanical pro le, through the magnetic pro le that it induces, to the digital output signal of the sensor. output polarity figure 3 shows the output polarity for the orientation of target and sensor shown in gure 2. the target direction of rotation 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 sensor output switching from high, i cc(high) , to low i cc(low) , as the leading edge of a tooth (a rising mechanical edge, as detected by the sensor) passes the sensor face. in this con guration, the device output current switches to its low polarity when a tooth is the target feature nearest to the sensor. if the direction of rota- tion 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 (gear) back-biasing magnet south pole north pole case (pin 1 side) (pin 4 side) hall ic pole piece element pitch (concentrator) dual-element hall effect device hall element 1 hall element 2 of sensor 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 tooth of the target gear is nearest the face of the sensor (see gure 3). a right-to-left (pin 4 to pin 1) rota- tion inverts the output signal polarity. figure 4: voltages pro les for high side and low side two-wire sensing. figure 3. output pro le of a ferrous target for the polarity indicated in gure 2. ats645 vcc gnd v cc i cc 1 4 v out(l) ats645 vcc gnd v cc 1 4 v out(h) i cc r sense r sense i out v out(h) v+ v out(l) v+ i+ representative differential magnetic profile target mechanical profile sensor electrical output profile, i out
true zero speed miniature differential peak- detecting gear tooth sensor ats645lsh 9 allegro microsystems, inc. 115 northeast cutoff, box 15036 worcester, massachusetts 01615-0036 (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 sensor is then automatically adjusted. figure 5 illustrates the effect of this feature. automatic offset adjust (aoa) the aoa is patented circuitry that automatically cancels the effects of chip, magnet, and installation offsets. (for capability, see dynamic offset cancellation, in the operating characteris- tics table.) this circuitry is continuously active, including both during calibration mode and running mode, compensating for any offset drift. continuous operation also allows it to compen- sate 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 sensor 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, a shown in the lowest panel. mechanical profile ag small ag large ag small ag large internal differential analog signal response, with agc internal differential analog signal response, without agc ferrous target v+ v+ figure 6: peak detecting switchpoint detail device output current b rp internal differential analog signal v+ i+ b op
true zero speed miniature differential peak- detecting gear tooth sensor ats645lsh 10 allegro microsystems, inc. 115 northeast cutoff, box 15036 worcester, massachusetts 01615-0036 (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 sensor 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. figure 7: typical application circuit ats645 vcc gnd v+ 0.01 1 4 f ecu pins 2 and 3 floating r 100 sense c byp
true zero speed miniature differential peak- detecting gear tooth sensor ats645lsh 11 allegro microsystems, inc. 115 northeast cutoff, box 15036 worcester, massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com sensor operation each operating mode is described in detail below. power-on when power (v cc > v ccmin ) is applied to the device, a short period of time is required to power the various portions of the ic. during this period, the ats645 is guaranteed to power-on in the high current state, i cc(high) . initial offset adjust the sensor intially 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 sensor 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. 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. any current level not within these ranges indicates a fault condition. running mode after the initial calibration period, c i , during which a signal gain is established, the device moves to running mode. during running mode, the sensor 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.
true zero speed miniature differential peak- detecting gear tooth sensor ats645lsh 12 allegro microsystems, inc. 115 northeast cutoff, box 15036 worcester, massachusetts 01615-0036 (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 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 = 4 ma, and r ja = 140 c/w, then: p d = v cc i cc = 12 v 4 ma = 48 mw t = p d r ja = 48 mw 140 c/w = 7c t j = t a + t = 25c + 7c = 32c 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 sh (i1 trim), using minimum-k pcb observe the worst-case ratings for the device, speci cally: r ja = 126c/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 126 c/w = 119 mw finally, invert equation 1 with respect to voltage: v cc(est) = p d(max) i cc(max) = 119 mw 16 ma = 7 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.
true zero speed miniature differential peak- detecting gear tooth sensor ats645lsh 13 allegro microsystems, inc. 115 northeast cutoff, box 15036 worcester, massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com package sh module 1.08 .043 8.0 .315 5.5 .217 0.43 .017 0.38 .015 5.0 .244 5.8 .228 4.0 .157 2.9 .114 1.7 .067 1 .039 0.6 .024 0.6 .024 1.27 .050 20.95 .825 13.05 .514 dimensions in millimeters. untoleranced dimensions are nominal. u.s. customary dimensions (in.) in brackets, for reference only 24 3 1 a a a b c c d d b dambar removal protrusion (16x) metallic protrusion, electrically connected to pin 4 and substrate (both sides) active area depth thermoplastic molded lead bar for alignment during shipment e e 0.75 .0294 0.75 .0294 hall elements (2x); controlling dimension inches e
true zero speed miniature differential peak- detecting gear tooth sensor ats645lsh 14 allegro microsystems, inc. 115 northeast cutoff, box 15036 worcester, massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 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 ca tions as 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 products are not authorized for use as critical compo- nents in life-support devices or sys tems without express written approval. 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. copyright ? 2004, 2006 allegro microsystems, inc.

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