memsic MXD7202GL/hl/ml/nl page 1 of 10 2003.08.04 applications low cost, low noise 2 g dual axis accelerometer with digital outputs MXD7202GL/hl/ml/nl features lo w co st reso lutio n better tha n 1 milli- g dual axis accelerometer fabricated on a monolithic cmos ic on chi p mi xed si gnal processi ng no moving parts; no loose particle issues >50,000 g shock survi val rati ng 5mm x 5mm x 2mm lcc package 2.7v to 5.25v single supply continuous operation compensated for sensitivity over temperature ultra lo w initia l z ero -g offset no adjustment needed outside security ? gas li ne/ e l e vat o r/ fat i gue sensi ng i nformation appliances ? c o m put er peri pheral s / p da?s/ m ouse sm art pens/ c el l phones MXD7202GL/hl/ml/nl functional block diagram gaming ? joystick/rf interface/menu selection/tilt sensing gps ? electro n i c co m p ass tilt co rrectio n consumer ? lc d project ors, pedom et ers, bl ood pressure monitor, digital cam eras general description the m xd7202gl/ hl/ m l/ nl i s a l o w cost , dual axi s accelerom eter fabricated on a standard, subm icron cmos process. it i s a com p l e t e sensi ng sy st em wi t h on-chi p m i xed si gnal processi ng. the m xd7202gl/ hl/ m l/ nl m easures acceleration with a full-scale range of 2 g an d a sen s itiv ity of 12.5%/g @5v. it can m easure both dynam i c acceleration (e.g. vibration) and static acceleration (e.g. gravity). the m xd7202gl/ hl/ m l/ nl desi gn i s based on heat convect i on and requi res no sol i d proof m a ss. thi s elim in ates stictio n an d p a rticle p r o b l em s asso ciated with co m p etitiv e d e v i ces an d p r o v i d e s sh o c k su rv iv al g r eater th an 50,000 g, lead in g to sig n i fican tly lo wer failu re rate an d lo wer l o ss due t o handl i ng duri ng assem b l y and at cust om er fi el d appl i cat i on. the m xd7202gl/ hl/ m l/ nl provi des t w o di gi t a l out put s that are set to 50% duty cycle at zero g acceleration. the out put s are di gi t a l wi t h dut y cy cl es (rat i o of pul se wi dt h t o period) that are proportional to acceleration. the duty cycle outputs can be directly interf aced to a m i croprocessor. t h e typi cal noi s e fl oor i s 0.3 m g / hz al l o w i ng si gnal s belo w 1 milli- g to be resolved at 1 hz bandwidth. t h e m xd7202gl/ hl/ m l/ nl i s packaged i n a herm et i cal l y sealed lcc surface m ount package (5 m m x 5 m m x 2 m m hei ght ) and i s operat i onal over a 0 c to 70 c(gl/hl) or a - 40 c to +85 c(m l /nl) tem p erature range. inform ation furnished by memsic is believe d to be accurate and reliable. however, no responsibility is assum e d by me msic for its use, nor for any infringem e nts of patents or other rights of th ird parties w h ich m a y result from its use. n o license is granted by im plication or otherw ise under any patent or patent rights of me msic. ? memsic, inc. 800 turnpik e st . , suit e 202, nort h andover, ma 01845 tel: 978. 738. 0900 f ax: 978. 738. 0196 www. m e m s i c . c o
m e m s ic m xd7202gl/ hl/ m l/ nl page 2 of 10 2003.08.04 mx d7202gl / hl / m l / nl spe c ificat ions (m eas urem ents @ 25 c, acceleration = 0 g unless otherwise noted; v dd = 5.0v unles s otherwis e s p ecified) parameter conditions min mx d7202gl/h l ty p. max min. mx d7202ml/n l ty p. max . uni t s sensor i n put measurement range 1 each axis 2.0 2.0 g nonlinearity best fit straight line 0.5 0.5 % of fs a lignment error 2 1.0 1.0 d e g r e e s alignment error x sensor to y sensor 0.01 0.01 degrees c r oss a x is sensitivity 3 0.5 0.5 % sen s itiv ity duty cycle per g duty cycle per g each axis v dd =5.0v v dd =3.0v 11.5 11.3 12.5 12.5 13.5 13.7 11.5 11.3 12.5 12.5 13.5 13.7 %/g %/g sensitivity c h a n g e o v e r temperature 4 d e lta from 25 c 1 0 1 5 % zero g bias level 0 g duty cycle 0 g duty cycle 0 g duty cycle 0 g duty cycle each axis v dd =5.0v v dd =5.0v v dd =3.0v v dd =3.0v 47 -0.24 46 -0.32 50 0.00 50 0.00 53 0.24 54 0.32 47 -0.24 46 -0.32 50 0.00 50 0.00 53 0.24 54 0.32 % g % g 0 g offset vs. temperature 4 d e lta from 25 c 1 . 5 1 . 5 m g / c noi se performance n o ise d e nsity, rms @25 c 0.3 0.8 0.3 0.8 m g / hz f r e q u e n c y r e s p o n s e 3db bandwidth 19 19 hz duty cycle output stage output high voltage out put low vol t a ge current t2 5 d r ift vs. temperature r i se/fall time source or sink @ 3.0v- 5.0v supply vs- 0 .2v -900 -750 200 0.2 250 -600 vs- 0 .2v -900 -750 200 0.2 250 -600 v v ua ppm/ c ns p o w e r s u p p l y operating voltage range 2.7 5.25 2.7 5.25 v quiescent supply current @5.0v 3.0 3.8 3.0 3.8 ma quiescent supply current @3.0v 3.4 4.3 3.4 4.3 ma turn-on time level (0g) 100 100 ms t e m p e r a t u r e r a n g e operating range 0 +70 -40 +85 c notes 1 g u aranteed by m easurem ent of initial offset and sensitivity . 2 alignm ent error is specifi ed as the angle between the true and indicated axis of sensitivity . 3 cross axis sensitivity is the algebrai c sum of the alignm ent and the inherent sensitivity errors. 4 d e fined as the output change from am bien t to m a xim u m tem p erature or am bient to mi n i mu m t e mp e r a t u r e . 5 duty cy cle period
m e m s ic m xd7202gl/ hl/ m l/ nl page 3 of 10 2003.08.04 model pwm frequency temperature range device weight MXD7202GL 100hz 0 t o 70 c <1.0 gram mxd7202hl 400hz 0 t o 70 c <1.0 gram mxd7202ml 100hz -40 t o +85 c <1.0 gram mxd7202nl 400hz -40 t o +85 c <1.0 gram absolute max i mum ratings* suppl y vol t a ge (v dd ) ??????...-0.5 to +7.0v storage tem p erature ???.????-65 c t o +150 c acceleration ??????????????..50,000 g *stresses above those liste d under a b solute maxim u m ratings m a y cause perm anent dam a ge to the device. t h is is a stress rating only ; the functional operation of the device at these or any other conditions above those indicated in the operational sections of this specification is not im p lied. e xposure to absolute m a xim u m rating conditions for extended periods m a y affect device reliability . pin description: lcc-8 package p i n n a m e d e s c r i p t i o n 1 nc do not connect 2 tp c onnect ed t o ground 3 c o m c o m m o n 4 yout y c h annel dut y c y cl e out put 5 xout x c h annel dut y c y cl e out put 6 nc do not connect 7 nc do not connect 8 v dd 2.7v t o 5.25v ordering guide all parts are shipped in tape and reel packaging. caution: esd (electrostatic discharge) sensitive device. note: the memsic logo?s arrow indicates the -x sensing direction of the device. the +y sensing direction is rotated 90 away from the +x direction following the right-hand rule. small circle indicates pin one(1). theory of operation the memsic device is a com p lete dual-axis acceleration m easu r em en t system fab r icated o n a m o n o lith ic cmos ic process. the devi ce operat i on i s based on heat t r ansfer by natural convection and opera tes like other accelerom eters havi ng a proof m a ss. the st at i onary el em ent , or ?proof m a ss?, in the memsic sensor is a gas. a sin g l e h eat so u r ce, cen tered in th e silico n ch ip is suspended across a cavity. equally spaced alum inum /polysilicon therm opiles (groups of t h erm o coupl es) are l o cat ed equi di st ant l y on al l four si des of the heat source (dual axis). under zero acceleration, a t e m p erat ure gradi e nt i s sy m m e t r i cal about t h e heat source, so th at th e tem p eratu r e is th e sam e at all fo u r th erm o p iles, causi ng t h em t o out put t h e sam e vol t a ge. acceleration in any direction will disturb the tem p erature profi l e , due t o free convect i on heat t r ansfer, causi ng i t t o be asy m m e t r i cal . the t e m p erat ure, and hence vol t a ge out put o f th e fo u r th erm o p iles will th en b e d i fferen t . th e d i fferen tial v o ltag e at th e th erm o p ile o u t p u t s is d i rectly proportional to the acceleration. there are two identical acceleration signal paths on the accelerom eter, one to m easure acceleration in the x-axis and one to m easure acceleration in the y-axis. please visit the memsic website at www.m e m s ic.com for a picture/graphic descri pt i on of t h e free convect i on heat t r ansfer pri n ci pl e.
m e m s ic m xd7202gl/ hl/ m l/ nl page 4 of 10 2003.08.04 yout ? thi s pi n i s t h e di gi t a l out put of t h e y-axi s acceleration sensor. it is fact ory program m a ble to 100hz or 400hz. the user shoul d ensure t h e l o ad i m pedance i s suffi ci ent l y hi gh as t o not source/ si nk >250 a typical. w h ile th e sen s itiv ity o f th is ax is h a s b een p r o g r am m e d at th e facto r y to b e th e sam e as th e sen s itiv ity fo r th e x - ax is, th e accelerom eter can be program m e d for non-equal sen s itiv ities o n th e x - an d y-ax es. co n t act th e facto r y fo r ad d itio n a l in fo rm atio n . mx d7202gl / hl / m l / nl pin de script ions v dd ? thi s i s t h e suppl y i nput for t h e ci rcui t s and t h e sensor heater in the accelerom eter . the dc vol t a ge shoul d be bet w een 2.7 and 5.25 vol t s . r e fer t o t h e sect i on on pc b l a y out and fabri cat i on suggest i ons for gui dance on ext e rnal part s and connect i ons recom m e nded. com ? thi s i s t h e ground pi n for t h e accelerom eter . tp ? thi s pi n shoul d be connect ed t o ground. xo u t ? thi s pi n i s t h e di gi t a l out put of t h e x-axi s acceleration sensor. it is fact ory program m a ble to 100hz or 400hz. the user shoul d ensure t h e l o ad i m pedance i s suffi ci ent l y hi gh as t o not source/ si nk >250 a typical. w h ile th e sen s itiv ity o f th is ax is h a s b een p r o g r am m e d at th e facto r y to b e th e sam e as th e sen s itiv ity fo r th e y-ax is, th e accelerom eter can be program m e d for non-equal sen s itiv ities o n th e x - an d y-ax es. co n t act th e facto r y fo r ad d itio n a l in fo rm atio n . discussion of tilt applications and resolution tilt applica t io ns: one of t h e m o st popul ar appl i cat i ons of the memsic accelerom eter product line is in tilt/inclination m easurem ent. an accelerom eter uses the force of gravi t y as an i nput t o det e rm i n e t h e i n cl i n at i on angl e of an object . a memsic accelerom eter is m o st sensitive to changes in position, or tilt, when the accelerom eter?s sensitive axis is p e rp en d i cu lar to th e fo rce o f g r av ity, o r p a rallel to th e earth?s surface. sim ilarly, wh en the accelerom eter?s axis is p a rallel to th e fo rce o f g r av ity (p erp e n d i cu lar to th e earth ? s surface), it is least sensitiv e to changes in tilt. tab l e 1 an d fig u r e 2 h e lp illu strate th e o u t p u t ch an g e s in th e x- an d y-ax es as th e u n it is tilted fro m +9 0 to 0 . not i ce t h at when one axi s has a sm al l change i n out put per d e g r ee o f tilt (in m g ), t h e second axi s has a l a rge change i n o u t p u t p e r d e g r ee o f tilt. th e co m p lem e n t ary n a tu re o f these two signals perm its low cost accurate tilt sensing to be achi e ved wi t h t h e m e m s ic devi ce (reference appl i cat i on not e an-00m x-007). m e m s i c figure 2: accelerometer po sition relative to gravity x - a x i s y - a x i s x-axis ori e nt at i on to earth?s surface (deg.) x output ( g ) c h ange per deg. o f tilt (m g ) y output ( g ) c h ange per deg. o f tilt (m g ) 9 0 - 1 . 0 0 0 0 . 1 5 0 . 0 0 0 1 7 . 4 5 8 5 - 0 . 9 9 6 1 . 3 7 0 . 0 8 7 1 7 . 3 7 8 0 - 0 . 9 8 5 2 . 8 8 0 . 1 7 4 1 7 . 1 6 7 0 - 0 . 9 4 0 5 . 8 6 0 . 3 4 2 1 6 . 3 5 6 0 - 0 . 8 6 6 8 . 5 9 0 . 5 0 0 1 5 . 0 4 4 5 - 0 . 7 0 7 1 2 . 2 3 0 . 7 0 7 1 2 . 2 3 3 0 - 0 . 5 0 0 1 5 . 0 4 0 . 8 6 6 8 . 5 9 2 0 - 0 . 3 4 2 1 6 . 3 5 0 . 9 4 0 5 . 8 6 1 0 - 0 . 1 7 4 1 7 . 1 6 0 . 9 8 5 2 . 8 8 5 - 0 . 0 8 7 1 7 . 3 7 0 . 9 9 6 1 . 3 7 0 0 . 0 0 0 1 7 . 4 5 1 . 0 0 0 0 . 1 5 table 1: changes in tilt for x- and y - axes resolution : the accelerom eter resolution is lim ited by n o i se. th e o u t p u t n o i se will v a ry with th e m easu r em en t bandwi d t h . w i t h t h e reduct i on of t h e bandwi d t h , by ap p l yin g an ex tern al lo w p a ss filter, th e o u t p u t n o i se d r o p s . red u c tio n o f b a n d w id th will im p r o v e th e sig n a l to n o i se rat i o and t h e resol u t i on. the out put noi se scal es di rect l y wi t h t h e square root of t h e m easurem ent bandwi d t h . the m a xi m u m am pl i t ude of t h e noi se, i t s peak- t o - peak val u e, approxi m a t e l y defi nes t h e worst case resol u t i on of t h e m easu r em en t. w ith a sim p le rc lo w p a ss filter, th e rm s n o i se is calcu lated as fo llo ws: noise (m g rm s) = noise(m g / hz ) * ) 6 . 1 * ) ( ( hz bandwidth the peak-t o-peak noi se i s approxi m a t e l y equal t o 6.6 t i m es the rm s value (for an averag e uncert a i n t y of 0.1%).
m e m s ic m xd7202gl/ hl/ m l/ nl page 5 of 10 2003.08.04 the m xd7202gl/ hl/ m l/ nl has t w o pw m dut y cy cl e outputs (x,y). the acceleration is proportional to the ratio t1/t2. the zero g out put i s set t o 50% dut y cy cl e and t h e sen s itiv ity scale facto r is set to 1 2 . 5 % d u t y cycle ch an g e per g . th ese n o m in al v a lu es are affected b y th e in itial t o l e rance of t h e devi ce i n cl udi ng zero g offset error and sen s itiv ity erro r. th is d e v i ce is o ffered fro m th e facto r y program m e d t o ei t h er a 10m s peri od (100 hz) or a 2.5m s peri od (400hz). digital interface the MXD7202GL/hl/ml/nl is easily interfaced with low cost m i crocontrollers. for th e digital output accelerom eter, one digital input port is requi red to read one accelerom eter output. for the analog output accel erom eter, m a ny low cost m i crocontrollers are available t oday that feature integrated a/ d (anal og t o di gi t a l convert ers) wi t h resol u t i ons rangi ng from 8 t o 12 bi t s . in m a ny appl i cat i ons t h e m i crocont rol l e r provi des an effective approach for the te m p erature com p ensation of the sen s itiv ity an d th e zero g offset. specific code set, reference desi gns, and appl i cat i ons not es are avai l a bl e from t h e fact ory . the fol l o wi ng param e t e rs m u st be consi d ered i n a digital interface: reso lu tio n : sm allest detectable ch ange in input acceleration bandw i d t h : detectable accelerations in a given period of tim e acqui si t i on ti me : the duration of the m easurem ent of the acceleration signal duty cycle definition t1 lengt h of t h e ?on? port i on of t h e cy cl e. t2 (peri od) lengt h of t h e t o t a l cy cl e. du ty cycle ratio o f th e ?0 n ? tim e (t1) of the cycle to the total cycle (t2). defined as t1/t2. pul s e wi dt h ti m e peri od of t h e ?on? pul se. defi ned as t1. t2 t1 a (g)= (t1/t2 - 0.5)/0.125 0g = 50% duty cy cle t2= 2.5ms or 10ms (factory programmable) figure 3: typical output duty c ycle choosing t2 and counter frequency design trade-offs the noise level is one determ inant of accelerom eter resol u t i on. the second rel a t e s t o t h e m easurem ent resol u t i on of t h e count er when decodi ng t h e dut y cy cl e output. the actual resolution of the acceleration signal is l i m i t e d by t h e t i m e resol u t i on of t h e count i ng devi ces used t o decode t h e dut y cy cl e. the fast er t h e count er cl ock, t h e hi gher t h e resol u t i on of t h e dut y cy cl e and t h e short e r t h e t2 peri od can be for a gi ven resol u t i on. tabl e 2 shows so m e o f th e trad e-o ffs. it is im p o r tan t to n o t e th at th is is th e resol u t i on due t o t h e m i croprocessors? count er. it i s probable that the accelerom ete r?s noise floor m a y set the lo wer lim it o n th e reso lu tio n . t2 (m s) memsic sa mple rate counter- clock rate (mhz) counts pe r t 2 cy cle counts per g reso- lution (m g ) 2 . 5 4 0 0 2 . 0 5000 6 2 5 1 . 6 2 . 5 4 0 0 1 . 0 2500 3 1 3 3 . 2 2 . 5 4 0 0 0 . 5 1250 1 5 6 6 . 4 1 0 . 0 1 0 0 2 . 0 20000 2 5 0 0 0 . 4 1 0 . 0 1 0 0 1 . 0 10000 1 2 5 0 0 . 8 1 0 . 0 1 0 0 0 . 5 5000 6 2 5 1 . 6 table 2: trade-offs between microcontroller counter rate and t2 period. converting the digital output to an analog output the pw m out put can be easi l y convert ed i n t o an anal og o u t p u t b y in teg r atio n . a sim p le rc filter can d o th e conversi on. not e t h at t h at t h e i m pedance of t h e ci rcui t fol l o wi ng t h e i n t e grat or m u st be m u ch hi gher t h an t h e im p e d a n ce o f th e rc filter. referen ce fig u r e 4 fo r an exam ple. 1uf dout aout 10k memsic accel. fi gure 4: c onvert i ng t h e di gi t a l out put t o an anal og vol t a ge
m e m s ic m xd7202gl/ hl/ m l/ nl page 6 of 10 2003.08.04 power supply noise rejection one capaci t o r i s recom m e nded for best reject i on of power suppl y noi se (reference fi gure 5 bel o w). the capaci t o r shoul d be l o cat ed as cl ose as possi bl e t o t h e devi ce suppl y pi n (v dd ). the capaci t o r l ead l e ngt h shoul d be as short as possible, and surface m ount capacitor is preferred. for typical applications, the capacitor can be ceram ic 0.1 f. pcb layout and fabrication suggestions 1. li beral use of ceram i c by pass capaci t o rs i s recom m e nded. 2. r obust l o w i nduct a nce ground wi ri ng shoul d be used. 3. c a re shoul d be t a ken t o ensure t h ere i s ?t herm al sy m m e t r y ? on t h e pc b i m m e di at el y surroundi ng t h e m e m s ic devi ce and t h at t h ere is no significant heat source nearby. 4. a m e t a l ground pl ane shoul d be added di rect l y beneat h t h e m e m s ic devi ce. the si ze of t h e pl ane shoul d be si m i l a r t o t h e m e m s ic devi ce?s foot pri n t and be as t h i c k as possi bl e. 5. vi as can be added sy m m e t r i cal l y around t h e ground plane. vias increase therm a l isolation of the device from the rest of the pcb. fi gure 5: power suppl y noi s e r e ject i o n
m e m s ic m xd7202gl/ hl/ m l/ nl page 7 of 10 2003.08.04 mx d7202gl/ hl/ m l/ nl typical performance characteristics ( @ 25 c , unless otherwise specified) v dd = 3v v dd = 5v 0% 5% 10% 15% 20% 25% 30% 35% 40% 45% 46 47 48 49 50 51 52 53 54 0% 10% 20% 30% 40% 50% 60% 70% 47 48 49 50 51 52 53 per c ent o f part s per c e n t o f part s % x-axi s zero g b i as di st ri but i on at xout , v dd =3v % x-axi s zero g b i as di st ri but i on at xout , v dd =5v 0% 5% 10% 15% 20% 25% 30% 35% 40% 45% 50% 46 47 48 49 50 51 52 53 54 0% 10% 20% 30% 40% 50% 60% 47 48 49 50 51 52 53 per c e n t o f part s per c e n t o f part s % y-axi s zero g b i as di st ri but i on at xout , v dd =3v % y-axi s zero g b i as di st ri but i on at xout , v dd =5v 0% 5% 10% 15% 20% 25% 11. 3 11. 9 12. 5 13. 1 13. 7 0% 5% 10% 15% 20% 25% 30% 35% 11. 5 12. 0 12. 5 13. 0 13. 5 per c e n t o f part s per c e n t o f part s %/g x-ax is sen s itiv ity distrib u tio n at xo u t , v dd =3v %/g x-ax is sen s itiv ity distrib u tio n at xo u t , v dd =5v
m e m s ic m xd7202gl/ hl/ m l/ nl page 8 of 10 2003.08.04 0% 5% 10% 15% 20% 25% 30% 11. 3 11. 9 12. 5 13. 1 13. 7 0% 5% 10% 15% 20% 25% 30% 35% 40% 45% 11. 5 12. 0 12. 5 13. 0 13. 5 per c e n t o f part s per c e n t o f part s %/g y-ax is sen s itiv ity distrib u tio n at yo u t , v dd =5v %/g y-ax is sen s itiv ity distrib u tio n at yo u t , v dd =3v 0. 90 0. 92 0. 94 0. 96 0. 98 1. 00 1. 02 1. 04 1. 06 1. 08 1. 10 -50 - 40 -30 - 20 -10 0 10 20 30 40 50 60 70 80 90 0. 90 0. 92 0. 94 0. 96 0. 98 1. 00 1. 02 1. 04 1. 06 1. 08 1. 10 -50 - 40 -30 - 20 -10 0 10 20 30 40 50 60 70 80 90 t( c ) no rm alized (with 2 5 c ) x-ax is sen s itiv ity v s . tem p eratu r e, v dd =5v t( c ) no rm alized (with 2 5 c ) y-ax is sen s itiv ity v s . tem p eratu r e, v dd =5v
m e m s ic m xd7202gl/ hl/ m l/ nl page 9 of 10 2003.08.04 49.0 49.5 50.0 50.5 51.0 51.5 52.0 52.5 - 5 0 - 40 - 3 0 - 20 - 1 0 0 10 20 30 40 50 60 70 80 90 o ffse t ( % ) 49. 0 49. 5 50. 0 50. 5 51. 0 51. 5 52. 0 52. 5 -50 - 40 -30 - 20 -10 0 10 20 30 40 50 60 70 80 90 o ffse t ( % ) t( c ) x-axis zero g offset vs. tem p erature, v dd =5v t( c ) y-axis zero g offset vs. tem p erature, v dd =5v
m e m s ic m xd7202gl/ hl/ m l/ nl page 10 of 10 2003.08.04 lcc-8 package drawing fig 6 : hermetica lly s e a l ed pa cka g e ou tlin e
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