rev. a information furnished by analog devices is believed to be accurate and reliable. however, no responsibility is assumed by analog devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. no license is granted by implication or otherwise under any patent or patent rights of analog devices. trademarks and registered trademarks are the property of their respective companies. one technology way, p.o. box 9106, norwood, ma 02062-9106, u.s.a. tel: 781/329-4700 www.analog.com fax: 781/326-8703 ? 2003 analog devices, inc. all rights reserved. ad22151 linear output magnetic field sensor features adjustable offset to unipolar or bipolar operation low offset drift over temperature range gain adjustable over wide range low gain drift over temperature range adjustable first order temperature compensation ratiometric to v cc applications automotive throttle position sensing pedal position sensing suspension position sensing valve position sensing industrial absolute position sensing proximity sensing functional block diagram temp ref i source demod switches out amp ref v cc /2 ad22151 general description the ad22151 is a linear magnetic field transducer. the sensor output is a voltage proportional to a magnetic field applied perpendicularly to the package top surface. the sensor combines integrated bulk hall cell technology and instrumentation circuitry to minimize temperature related drifts associated with silicon hall cell characteristics. the architecture maximizes the advantages of a monolithic implementation while allowing sufficient versatility to meet varied application require- ments with a minimum number of components. principal features include dynamic offset drift cancellation and a built-in temperature sensor. designed for single 5 v supply operation, the ad22151 achieves low drift offset and gain op eration over ?0 c to +150 c. temperature compensa- tion can accommodate a number of magnetic materials commonly utilized in economic position sensor assemblies. the transducer can be configured for specific signal gains to meet various application requirements. output voltage can be adjusted from fully bipolar (reversible) field operation to fully unipolar field sensing. the voltage output achieves near rail-to-rail dynamic range, capable of supplying 1 ma into large capacitive loads. the signal is ratiometric to the positive supply rail in all configurations. nc r1 gnd r3 r2 v cc ad22151 nc = no connect output 0.1 f figure 1. typical bipolar configuration with low (< ?00 ppm) compensation nc r1 gnd r3 r2 v cc ad22151 nc = no connect output 0.1 f r4 figure 2. typical unipolar configuration with high ( ?000 ppm) compensation
rev. a e2e ad22151especifications (t a = 25 c and v+ = 5 v, unless otherwise noted.) parameter min typ max unit operation v cc operating 4.5 5.0 6.0 v i cc operating 6.0 10 ma input tc3 (pin 3) sensitivity/volt 160 m v/g/v input range 1 v cc 2 05 . v output 2 sensitivity (external adjustment, gain = +1) 0.4 mv/g linear output range 10 90 % of v cc output min 5.0 % of v cc output max (clamp) 93 % of v cc drive capability 1.0 ma offset @ 0 gauss v cc 2 v offset adjust range 5.0 95 % of v cc output short circuit current 5.0 ma accuracies nonlinearity (10% to 90% range) 0.1 % fs gain error (over temperature range) 1% offset error (over temperature range) 6.0 g uncompensated gain tc (g tcu ) 950 ppm ratiometricity error 1.0 %v/v cc 3 db roll-off (5 mv/g) 5.7 khz output noise figure (6 khz bw) 2.4 mv/rms package 8-lead soic operating temperature range e40 +150 r c notes 1 e40 r c to +150 r c. 2 r l = 4.7 k w . specifications subject to change without notice. caution esd (electrostatic discharge) sensitive device. electrostatic charges as high as 4000 v readily accumulate on the human body and test equipment and can discharge without detection. although the ad22151 features proprietary esd protection circuitry, permanent damage may occur on devices subjected to high energy electrostatic discharges. therefore, proper esd precautions are recommended to avoid performance degradation or loss of functionality. absolute maximum ratings * supply voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 v package power dissipation . . . . . . . . . . . . . . . . . . . . . . 25 mw storage temperature . . . . . . . . . . . . . . . . . . . e50 r c to +160 r c output sink current, i o . . . . . . . . . . . . . . . . . . . . . . . . 15 ma magnetic flux density . . . . . . . . . . . . . . . . . . . . . . unlimited lead temperature (soldering 10 sec) . . . . . . . . . . . . . . 300 r c * stresses above those listed under absolute maximum ratings may cause perma- nent damage to the device. this is a stress rating only; functional operation of the device at these or any other conditions above those indicated in the operational sections of this specification is not implied. exposure to the absolute maximum rating conditions for extended periods may affect device reliability. ordering guide temperature package package model range description option ad22151yr e40 r c to +150 r c 8-lead soic r-8 ad22151yr-reel e40 r c to +150 r c 8-lead soic r-8
rev. a ad22151 e3e pin configuration top view (not to scale) 8 7 6 5 1 2 3 4 area of sensitivity * tc1 tc2 tc3 gnd v cc ref gain output ad22151 (not to scale) 8 7 6 5 1 2 3 4 * shaded area represents magnetic field area of sensitivity (20mils 20mils) positive b field into top of package results in a positive voltage response circuit operation the ad22151 consists of epi hall plate structures located at the center of the die. the hall plates are orthogonally sampled by commutation switches via a differential amplifier. the two amplified hall signals are synchronously demodulated to provide a resultant offset cancellation (see figure 3). the demodulated signal passes through a noninverting amplifier to provide final gain and drive capability. the frequency at which the output signal is refreshed is 50 khz. temperature e c 140 e40 120 100 80 60 40 20 0 e20 e0.004 offset e v e0.003 e0.002 e0.001 0 0.001 0.002 0.003 0.004 0.005 figure 3. relative quiescent offset vs. temperature temperature dependencies the uncompensated gain temperature coefficient (g tcu ) of the ad22151 is the result of fundamental physical properties asso- ciated with silicon bulk hall plate structures. low doped hall plates operated in current bias mode exhibit a temperature relationship determined by the action of scattering mechanisms and doping concentration. the relative value of sensitivity to magnetic field can be altered by the application of mechanical force upon silicon. the mecha- nism is principally the redistribution of electrons throughout the pin function descriptions pin no. description connection 1t emperature compensation 1 output 2t emperature compensation 2 output 3t emperature compensation 3 input/output 4g round 5o utput output 6 gain input 7r eference output 8 positive power supply valleys of the silicon crystal. mechanical force on the sensor is attributable to package-induced stress. the package material acts to distort the encapsulated silicon, altering the hall cell gain by 2% and g tcu by 200 ppm. figure 4 shows the typical g tcu characteristic of the ad 22151. this is the observable alteration of gain with respect to tempera- ture with pin 3 (tc3) held at a constant 2.5 v (uncompensated). if a permanent magnet source used in conjunction with the sensor also displays an intrinsic tc (b tc ), it will require fac toring into the total temperature compensation of the sensor assembly. figures 5 and 6 represent typical overall temperature/gain per- formance for a sensor and field combination (b tc = e200 ppm). figure 5 is the total drift in volts over a e40 r c to +150 r c tem- perature range with respect to applied field. figure 6 represents typical percentage gain variation from 25 r c. figures 7 and 8 show similar data for a b tc = e2000 ppm. temperature e c 14 e4 e40 % gain 10 60 110 160 12 4 2 0 e2 10 6 8 e6 figure 4. uncompensated gain variation (from 25 r c) vs. temperature
rev. a e4e ad22151 field e gauss e600 400 e400 e200 0 200 0 delta signal e v 0.005 0.010 0.015 0.020 0.025 600 figure 5. signal drift over temperature (e40 r c to +150 r c) vs. field (e200 ppm); 5 v supply temperature e c 0.25 % gain 0.20 0 0.15 0.05 0.10 e40 10 60 110 160 e0.05 figure 6. gain variation from 25 r c vs. temperature (e200 ppm) field; r1 e15 k w field ? gauss ?600 400 ?400 ?200 0 200 delta signal ? v 0 0.010 0.015 0.020 0.025 600 0.005 0.045 0.040 0.030 0.035 ?800 800 figure 7. signal drift over temperature (e40 r c to +150 r c) vs. field (e2000 ppm); 5 v supply temperature e c 2.0 1.8 1.0 1.6 1.2 1.4 e40 10 60 110 160 e0.2 0.8 0.6 0.4 0.2 0 % gain figure 8. gain variation (from 25 r c) vs. temperature (e2000 ppm field; r1 = 12 k w ) temperature compensation the ad22151 incorporates a thermistor transducer that detects relative chip temperature within the package. this function provides a compensation mechanism for the various temperature dependencies of the hall cell and magnet combina- tions. the temperature information is accessible at pins 1 and 2 ( +2900 ppm/ r c) and pin 3 ( e2900 ppm/ r c), as repre- sented by figure 9. the compensation voltages are trimmed to converge at v cc /2 at 25 r c. pin 3 is internally connected to the negative tc voltage via an internal resistor (see the func- tional block diagram). an external resistor connected between pin 3 and pins 1 or 2 will produce a potential division of the two complementary tc voltages to provide optimal compensa- tion. the pin 3 internal resistor provides a secondary tc designed to reduce second order hall cell temperature sensitivity. temperature e c 1.0 volts e reference 0.8 0 0.6 0.2 0.4 150 112 74 e2 e40 e0.2 e0.4 e0.6 e0.8 e1.0 36 tc1, tc2 volts tc3 volts figure 9. tc1, tc2, and tc3 with respect to reference vs. temperature the voltages present at pins 1, 2, and 3 are proportional to the supply voltage. the presence of the pin 2 internal resistor dis- tinguishes the effective compensation ranges of pins 1 and 2. (see temperature configuration in figures 1 and 2, and typical resistor values in figures 10 and 11.) variation occurs in the operation of the gain temperature com- pensation for two reasons. first, the die temperature within the package is somewhat higher than the ambient temperature due
rev. a ad22151 e5e to self-heating as a function of power dissipation. second, pack- age stress effect alters the specific operating parameters of the gain compensation, particularly the specific crossover tempera- ture of tc1, tc3 ( 10 r c). configuration and component selection there are three areas of sensor operation that require external component selection: temperature compensation (r1), signal gain (r2 and r3), and offset (r4). temperature if the internal gain compensation is used, an external resistor is required to complete the gain tc circuit at pin 3. a number of factors contribute to the value of this resistor: a. the intrinsic hall cell sensitivity tc 950 ppm. b. package induced stress variation in a. 150 ppm. c. specific field tc e200 ppm (alnico), e2000 ppm (ferrite), 0 ppm (electromagnet), and so on. d. r1, tc. the final value of target compensation also dictates the use of either pin 1 or pin 2. pin 1 is provided to allow for large nega- tive field tc devices such as ferrite magnets; thus, r1 would be connected to pins 1 and 3. pin 2 uses an internal resistive tc to optimize smaller field coefficients such as alnico down to 0 ppm coefficients when only the sensor gain tc itself is dominant. because the tc of r1 itself will also affect the compensation, a low tc resistor ( 50 ppm) is recommended. figures 10 and 11 indicate r1 resistor values and their associ- ated effectiveness for pins 1 and 2, respectively. note that the indicated drift response in both cases incorporates the intrinsic hall sensitivity tc (b tcu ). for example, the ad22151 sensor is to be used in conjunction with an alnico material permanent magnet. the tc of such mag- nets is e200 ppm (see figures 5 and 6). figure 11 indicates that a compensating drift of 200 ppm at pin 3 requires a nomi- nal value of r1 = 18 k w (assuming negligible drift of r1 itself). r1 e k 3500 drift e ppm 3000 1000 2500 1500 2000 0510 20 25 500 0 15 30 figure 10. drift compensation (pins 1 and 3) vs. typical resistor value r1 r1 e k 800 drift e ppm 600 e200 400 0 200 0510 20 25 e400 e600 15 30 35 40 45 50 figure 11. drift compensation (pins 2 and 3) vs. typical resistor value r1 gain and offset the operation of the ad22151 can be bipolar (i.e., 0 gauss = v cc /2), or a ratiometric offset can be implemented to position zero gauss point at some other potential (i.e., 0.25 v). the gain of the sensor can be set by the appropriate r2 and r3 resistor values (see figure 1) such that: gin r r mv g a =+ 1 3 2 04 ./ (1) however, if an offset is required to position the quiescent out- put at some other voltage, the gain relationship is modified to: gin r rr mv g a =+ () 1 3 24 04 ./ (2) the offset that r4 introduces is: offset r rr vv cc out =+ + () () 1 3 24 e (3) for example, at v cc = 5 v at room temperature, the internal gain of t he sensor is approximately 0.4 mv/gauss. if a sensitivity of 6 mv/gauss is r equired with a quiescent output voltage of 1 v, the calculations below apply (see figure 2). a value would be selected for r3 that complied with the various considerations of current and power dissipation, trim ranges (if applicable), and so on. for the purpose of example, assume a value of 85 k w . to achieve a quiescent offset of 1 v requires a value for r4 as: v v cc cc 2 1 0 375 ? ? ? = e . (4) thus: r k kk 4 85 0 375 85 141 666 = ? ? ? = w ww . e. (5) the gain required would be 6/0.4 (mv/gauss) = 15.
rev. a ? ad22151 knowing the values of r3 and r4 and noting e quation 2, the parallel combination of r2 and r4 required is: 85 15 1 6 071 k k ? ? ? . () = thus: r kk k 2 1 1 6 071 1 141 666 6 342 = ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? = . ? . . ?? ? noise the principal noise component in the sensor is thermal noise from the hall cell. clock feedthrough into the output signal is largely suppressed with application of a supply bypass capacitor. figure 12 shows the power spectral density (psd) of the output signal for a gain of 5 mv/gauss. the effective bandwidth of the sensor is approximately 5.7 khz, as shown in figure 13. the psd indicates an rms noise voltage of 2.8 mv within the 3 db bandwidth of the sensor. a wideband measurement of 250 mhz indicates 3.2 mv rms (see figure 14a). in many position sensing applications, bandwidth requirements can be as low as 100 hz. passing the output signal through a 100 hz lp filter, for example, would reduce the rms noise volt- age to 1 mv. a dominant pole may be introduced into the out put amplifier response by connection of a capacitor across feedback resistor r3 as a simple means of reducing noise at the expense of bandwidth. figure 14b indicates the output signal of a 5 mv/g sensor bandwidth limited to 180 hz with a 0.01 f feedback capacitor. note: measurements were taken with a 0.1 f decoupling capacitor between v cc and gnd at 25 c. logmag 5 db/div 100 h 1 h start: 64hz noise: psd ( 8mv/gauss ) stop: 25.6khz rms: 64 b marker 64hz y: 3.351 h figure 12. power spectral density (5 mv/g) gain ?mv/gauss 23 4 56 frequency ?khz 0 2 3 4 5 1 6 7 1 3db frequency (khz) figure 13. small signal gain bandwidth vs. gain ch2 10.0mv b w m2.00ms [ [ t 3acqs ch2 p-p 19.2mv tek stop: 25.0 ks/s figure 14a. peak-to-peak full bandwidth (10 mv/division) b w m2.00ms [ [ t 7acqs ch2 p-p 4.4mv tek stop: 25.0 ks/s ch2 10.0mv figure 14b. peak-to-peak 180 hz bandwidth (10 mv/division)
rev. a ad22151 e7e outline dimensions 8-lead standard small outline package [soic] narrow body (r-8) dimensions shown in millimeters and (inches) 0.25 (0.0098) 0.19 (0.0075) 1.27 (0.0500) 0.41 (0.0160) 0.50 (0.0196) 0.25 (0.0099) 45 8 0 1.75 (0.0688) 1.35 (0.0532) seating plane 0.25 (0.0098) 0.10 (0.0040) 85 4 1 5.00 (0.1968) 4.80 (0.1890) 4.00 (0.1574) 3.80 (0.1497) 1.27 (0.0500) bsc 6.20 (0.2440) 5.80 (0.2284) 0.51 (0.0201) 0.33 (0.0130) coplanarity 0.10 controlling dimensions are in millimeters; inch dimensions (in parentheses) are rounded-off millimeter equivalents for reference only and are not appropriate for use in design compliant to jedec standards ms-012aa field e gauss 0.06 0.05 0.04 0.02 0.03 e600 e400 e200 0 200 400 600 0.01 0 e0.01 e0.02 e0.03 e0.04 e0.05 % error figure 15. integral nonlinearity vs. field temperature e c 2.496 volts 2.494 2.492 2.488 2.490 140 120 100 80 60 40 20 2.486 2.484 0 e40 e20 gain = 3.78mv/g figure 16. absolute offset volts vs. temperature
rev. a c00675e0e2/03(a) printed in u.s.a. e8e ad22151 revision history location page 2/03?data sheet changed from rev. 0 to rev. a. change to ordering guide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 updated outline dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
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