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document number: mc33941 rev. 4 freescale semiconductor technical data ? freescale semiconductor, in c., 2008. all rights reserved. electric field imaging device the mc33941 is intended for cost-sensitive applications where non-contact sensing of objects is desired. when connected to external electrodes, an electric field is created. the mc33941 dete cts objects in this electric field. the ic generates a low-frequency sine wave, which is adjustable by using an external resistor and is optimized for 120 khz. the sine wave has very low harmonic content to reduce harmonic interference. the mc33941 also contains support circuits for a micr ocontroller unit (mcu) to allow the construction of a two-chip e-field system. features ? supports up to 7 electrodes ? shield driver for driving remote electrodes through coaxial ? high-purity sine wave generator tunable with external resistor ? response time tunable with external capacitor ? +5v regulator to power external circuit ? can support up to 28 touch pad sensors (2 way multiplexing) ? extended temperature range -40 to 110c ? pb-free and rohs compliant typical applications ? appliance control panels and touch sensors ? linear and rotational sliders ? spill over flow sensing measurement ? refrigeration frost sensing ? industrial control and safety systems security ? proximity detection for wake-up features ? touch screens ? garage door safety sensing ? pc peripherals ? patient monitoring ? point of sale terminals ? size detection ? liquid level sensing ordering information device name temperature range drawing package mc33941eg/r2 -40 to 110c 98asb42564b soicw-24 mc33941 electronic field imaging device eg suffix (pb-free) 24-terminal soicw case 751e-05 n/c e7 e6 e5 e4 e3 e2 e1 test gnd shield agnd dgnd n/c shielden c b a level lpcap rosc vddcap vpwr vcccap pin connections
mc33941 sensors 2 freescale semiconductor figure 1 simplified functional block diagram osc 700 700 level lpcap vddcap vcccap vpwr agnd gnd rosc shielden shield e1-e7 a,b,c 150 rect lpf gain and offset mux in control logic mux out 3 22 k (nominal) 2.8 k 2.8 k v cc reg v dd reg
mc33941 sensors freescale semiconductor 3 table 1. maximum ratings all voltages are with respect to ground unless otherwise noted. exceeding these ratings may cause a malfunction or permanent damage to the device. rating symbol value unit electrical ratings peak v pwr voltage v pwrpk 40 v double battery 1 minute maximum t a = 30 c v dblbat 26.5 v esd voltage human body model (c zap = 100 pf, r zap = 1500 w) machine model (c zap = 200 pf, r zap = 0 w) charge device model (cdm), robotic (c zap = 4.0pf) v esd 2000 200 1200 v thermal ratings storage temperature t stg -55 to 150 c operating ambient temperature t a -40 to 110 c operating junction temperature t j -40 to 150 c thermal resistance junction-to-ambient (1) junction-to-case (2) junction-to-board (3) r ja r jc r jb 41 0.2 3.0 c/w soldering temperature (4) notes 1. junction temperature is a function of on-chip power dissipati on, package thermal resistance, mounting site (board) temperatur e, ambient temperature, air flow, power dissipation of other components on the board, and board thermal resistance. in accordance with sem i g38- 87 and jedec jesd51-2 with the single layer board horizontal. 2. indicates the average thermal resistance between the die and the case top surface as measured by the cold plate method (milsp ec 883 method 1012.1) with the cold plate temperature used for the case temperature. 3. thermal resistance between the die and the printed circuit board per jedec jesd51-8. board temperature is measured on the top surface of the board near the package. 4. terminal soldering temperature limit is for 10 seconds maximu m duration. the device is not des igned for immersion soldering. exceeding these limits may cause malfunction or permanent damage to the device.
mc33941 sensors 4 freescale semiconductor table 2. static electrical characteristics characteristics noted under conditions 5.5 v v sup 18 v, -4 0 c t a 110 c, gnd = 0 v unless otherwise noted. typical values noted reflect the approximate parameter means at t a = 25c under nominal conditi ons unless otherwise noted. characteristic symbol min typ max unit supply (v pwr ) supply voltage v pwr 9.0 12 18 v i dd (v pwr = 14v) (quiescent supply current measur ed over temperature. assumes that no external devices connecte d to internal voltage regulators) i dd 6.0 7.0 8.0 ma voltage regulator 5v regulator voltage 7.0 v vpwr 18 v, 1.0 ma i l 75 ma, c filt = 47 f vcccap 4.75 5 5.25 v electrode signals (e1?e7) total variance between electrode measurements (5) all c load = 15 pf elv var ? ? 3.0 % electrode maximum harmonic level below fundamental (5) 5.0 pf c load 150 pf el harm ? -20 ? db electrode transmit output range 5.0 pf c load 150 pf el txv 1.0 ? 8.0 v receive input voltage range rx v 0 ? 9.0 v grounding switch on voltage (6) i sw = 1.0 ma sw von ? ? 5.0 v logic i/o (c, b, a) cmos logic input low threshold v thl 0.3 ? ? v cc logic input high threshold v thh ? ? 0.7 v cc voltage hysteresis v hys ? 0.06 ? v cc input current v in = v cc v in = 0 v i in 10 -5.0 ? ? 50 5.0 a signal detector (lpcap) detector output resistance det ro ? 50 ? k lpcap to level gain a rec 3.6 4.0 4.4 a v lpcap to level offset v recoff -3.3 -3.0 -2.7 v notes 5. verified by design and characte rization. not tested in production. 6. current into grounded terminal under test = 1.0 ma.
mc33941 sensors freescale semiconductor 5 table 3. dynamic electrical characteristics (7) characteristics noted under conditions 5.5 v v sup 18 v, -40 c t a 110 c, gnd = 0 v unless otherwise noted. typical values noted reflect the approximate parameter means at t a = 25c under nominal conditions unless otherwise noted. characteristic symbol min typ max unit osc (rosc) osc frequency stability f stab ? ? 10 % osc center frequency rosc = 39 k rosc = 20 k rosc = 82 k f osc ? ? ? 120 240 60 ? ? ? khz harmonic content 2nd through 4th harmonic level 5th and higher osch arm ? ? ? ? -20 -60 db shield driver (shield) shield driver maximum harm onic level below fundamental 10 pf c load 500 pf sd harm ? -20 ? db shield driver gain bandwidth product measured at 120 khz sd gbw ?4.5 ? mhz notes 7. all parameters are guaranteed by design.
mc33941 sensors 6 freescale semiconductor principle of operation the 33941 generates a low radio frequency sine wave with nominal 5.0 v peak-to-peak amplitude. the frequency is set by an external resistor and is optimized for 120 khz. an internal multiplexer routes the signal to one of the 7 terminals under control of the abc in put terminals. a receiver multiplexer simultaneously connected to the selected electrode and routes its signal to a detector, which converts the sine wave to a dc level. the dc level is filtered by an external capacitor, is multiplied and offset to increase sensitivity. all electrode out puts are grounded internally by the device when not selected. the amplitude and phase of the sinusoidal wave at the electrode are affected by objects in proximity. a ?capacitor? is formed between the driving electrode and the object, each forming a ?plate? that holds the electric charge. the voltage measured is an inverse function of the capacitance between the electrode being measured, the surrounding electrodes, and other objects in the electric field surrounding the electrode. increasing capacitance results in decreasing voltage. the value of the series resistor (22kohm) was chosen to provide a near linear relationship at 120 khz over a range of 10pf to 70pf. while exploring applications using the e-field chip, it is always useful to approach the problem using the capacitor model. figure 2 . conceptual block diagram capacitor model the capacitance measured by the e-field ic is: ? proportional to the area of the electrode ? proportional to the dielectric constant of the material between the electrodes ? inversely proportional to the distance between the objects figure 3. capacitor model detector low pass filter voltage level proportional to 1/c (voltage divider) drive level ~ 5 v p-p load resistor (22 k ohms) sine generator (120 khz) detected signal level decreases with increasing capacitance electrodes capacitance increases as electrodes move closer together capacitor model virtual ground stray variable capacitance object detector low pass filter voltage level proportional to 1/c (voltage divider) drive level ~ 5 v p-p load resistor (22 k ohms) sine generator (120 khz) detected signal level decreases with increasing capacitance electrodes capacitance increases as electrodes move closer together capacitor model virtual ground stray variable capacitance object d a k c 0 = c k d c=the capacitance in farads (f) a=the area of the plates in square meters (m2) d=the distance between the plates in meters (m) k=the dielectric constant of t he material separating the plates 0=is the permittivity of free space (8.85 x 10-12 f/m) table 4 dielectric constants of various materials dielectric material thickness (mil) k acrylic 84.5 2.4-4.5 glass 74.5 7.5 nylon plastic 68 3.0-5.0 polyester film 10 3.2 flexible vinyl film 9 2.8-4.5 air - 1 water - 80 ice - 3.2 automotive oil - 2.1
mc33941 sensors freescale semiconductor 7 features shield driver a shield driver is included to minimize the electrode signal along wires. this circuit provides a buffered version of the returned ac signal from the elec trode. since it has nearly the same amplitude and phase as the electrode signal, there is little or no potential difference between the two signals, thereby canceling out any electric field. in effect, the shield drive isolates the electrode signal from external virtual grounds. a common application is to connect the shield driver to the shield of a coax cable used to connect an electrode to the corresponding electrode terminal. another typical use is to drive a ground plane that is used behind an array of touch sensor electrodes in order to cancel out any virtual grounds that could attenuate the ac signal. tunable frequency the 33941 offers 3 operating frequencies. in addition to the default frequency of 120 khz, the 33941 has also been characterized to work in two other frequencies (240 khz and 60 khz) for applications with specific needs. these frequencies are tunable by attaching a 20k and 82k resistor at rosc respectively. if a wider capacitance range is needed, simply change the rosc resistor value to 82k to have the signal generator operate at 60 khz which will extend the capacitance range to 150pf as seen on figure 4 . the figure also shows that one can achieve higher sensitivity at lower capacitances by setting the rosc resistor value to 20k. all resistor values listed above are for 5% tolerance resistors. adjustable response time the rectified sine wave is filtered by a low pass filter formed by and internal resistor and an external capacitor attached to lp_cap. the value of the external capacitor is selected to allow the designer to optimize the balance between noise and settling time. a typical value for the external capacitor is 10nf and in practice it will have a response time of 1.5ms . if faster response time is required a 1nf capacitor can be used and it will have response times <200 s . please note that reducing the lp_cap capacitor value increases noise accordingly. figure 4 . output voltage vs. capacitance at 3 discrete frequencies output voltage vs capacitance at 3 discrete frequencies 0 0.5 1 1.5 2 2.5 3 3.5 4 0 20 40 60 80 100 120 140 160 capacitance (pf) voltage output (volts) 120 khz 240 khz 60 khz
mc33941 sensors 8 freescale semiconductor basic connections pin descriptions figure 5. pin descriptions figure 6 . simplified application diagram table 5. electrode selection terminal/signal c b a no electrodes selected 0 0 0 e1 0 0 1 e2 0 1 0 e3 0 1 1 e4 1 0 0 e5 1 0 1 e6 1 1 0 e7 1 1 1 n/c e7 e6 e5 e4 e3 e2 e1 test gnd shield agnd dgnd n/c shielden c b a level lpcap rosc vddcap vpwr vcccap table 6. pin description pin number pin name definition 1 dgnd connected to the ground return 2, 24 n/c these pins should be left open. 3 shielden used to enable the shield signal 4,5,6 c, b, a controls electrode or reference activity 7 level this is the detected, amplified, and offset representation of the signal voltage on the selected electrode 8 lpcap a capacitor on this pin forms a low pass filter with the internal series resistance from the detector to this pin 9 rosc a resistor from this pin to circuit ground determines the operating frequency of the oscillator 10 vddcap a 47 f capacitor is connected to this pin to filter the internal analog regulated supply 11 vpwr 12 v power applied to this pin will be converted to the internal regulated voltages needed to operate the part 12 vcccap a 47 f capacitor is connected to this pin and vcccap provides a regulated 5.0 v to power external circuits 75 ma max 13 agnd connected to the ground return of the analog circuitry 14 shield connects to cable shields to cancel cable capacitance. 15 gnd main ic ground 16 test connect to circuit ground 17-23 e1?e7 electrode pins mc33941 field electrodes (e1 through e7) mcu shielden agnd test rosc gnd vddcap e1 e7 shield vpwr analog in electrode select shield enable lpcap level a, b, c vcccap 3 +12v 39k 10nf 47uf 47uf power +5v
package dimensions case 751e-05 issue g 24-lead soic page 1 of 2 sensors freescale semiconductor 9 mc33941
package dimensions case 751e-05 issue g 24-lead soic page 2 of 2 mc33941 sensors 10 freescale semiconductor
mc33941 rev. 4 09/2008 information in this document is provided solely to enable system and software implementers to use freescale semiconduc tor products. there are no express or implied copyright licenses granted hereunder to design or fabricate any integrated circuits or integrated circuits based on the information in this document. freescale semiconductor reserves the right to make changes without further notice to any products herein. freescale semiconductor makes no warranty, representation or guarantee regarding the suitability of its products for any particular purpose, nor does freescale semiconductor assume any liability ar ising out of the applic ation or use of any product or circuit, and specifically disclai ms any and all liability, including without limitation consequential or incidental damages. ?typical? parameters that may be provided in freescale semiconductor data shee ts and/or specifications can and do vary in different applications and actual performance may vary over time. all operating parameters, including ?typicals?, must be validated for each customer application by customer?s technical experts. freescale se miconductor does not convey any license under its patent rights nor the rights of others. freescale semiconductor products are not designed, intended, or authorized for use as components in systems intended for surgical implant into the body, or other applications intended to support or sustain life, or for any other application in which the fa ilure of the freescale semiconductor product could create a situation where personal injury or death may occur. should buyer purchase or use freescale semiconductor products for any such unintended or unauthorized application, buyer shall indemnify and hold freescale semiconductor and its officers, employees, subsidiaries, affili ates, and distributors harmless against all claims, costs, damages, and expenses, and reasonable attorney fees arising out of, directly or indirectly, any claim of perso nal injury or death associated with such unintended or unauthorized use, even if such claim alleges that freescale semiconductor was negligent regarding the design or manufacture of the part. freescale? and the freescale logo are trademarks of freescale semiconductor, inc. all other product or service names are the property of their respective owners. ? freescale semiconductor, inc. 2008. all rights reserved. how to reach us: home page: www.freescale.com web support: http://www.freescale.com/support usa/europe or locations not listed: freescale semiconductor, inc. technical information center, el516 2100 east elliot road tempe, arizona 85284 1-800-521-6274 or +1-480-768-2130 www.freescale.com/support europe, middle east, and africa: freescale halbleiter deutschland gmbh technical information center schatzbogen 7 81829 muenchen, germany +44 1296 380 456 (english) +46 8 52200080 (english) +49 89 92103 559 (german) +33 1 69 35 48 48 (french) www.freescale.com/support japan: freescale semiconductor japan ltd. headquarters arco tower 15f 1-8-1, shimo-meguro, meguro-ku, tokyo 153-0064 japan 0120 191014 or +81 3 5437 9125 support.japan@freescale.com asia/pacific: freescale semiconductor china ltd. exchange building 23f no. 118 jianguo road chaoyang district beijing 100022 china +86 010 5879 8000 support.asia@freescale.com for literature requests only: freescale semiconductor literature distribution center p.o. box 5405 denver, colorado 80217 1-800-441-2447 or +1-303-675-2140

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