unisonic technologies co., ltd m7240 cmos ic www.unisonic.com.tw 1 of 7 copyright ? 2011 unisonic technologies co., ltd qw-r502-682.a 3 1/2 lcd display driver, a/d converters ? description the utc m7240 is a low voltage power supply of three half a/d conversion ic. with the m7240 , the product can be assembled the digital gauge outfit and digital multimeters with 3v batteries supply. the m7240 has hare the following features: using the only two batteries of 7v or a 3v lithium batteries can work for long time the chip contains an internal cloc k generator which can be fine-tuned by a resistor, slicing the band gap in design makes the benchmark signals shift and temperature shift noise greatly improve, slicing the negative power produced within t he circuit design, the maximum load current can reach to 2ma. ? features *power supply voltage:2.5v ~ 6v *external clock circuit within a resistor, used for clock frequency fine-tuning *built-in close bandgap refere nce, low temperature drift *high input impedance *low noise a/d converter *guaranteed zero reading with zero input. *has triggered buttons that keep and low voltage alarm function that power *direct driver lcd display ? ordering information ordering number package packing lead free halogen free m7240l-ql1-y m7240g-q l1-y lqfp-44 tray
m7240 cmos ic unisonic technologies co., ltd 2 of 7 www.unisonic.com.tw qw-r502-682.a ? pin configurations ? pin description pin name type pin description 1 3 41 44 a1~g1 o lcd segment drive 4 9 21 a2~g2 o lcd segment drive 10~13 18~20 a3~g3 o lcd segment drive 14 ab4 o lcd segment drive 15 pol o lcd drive display minus "-" 16 bp o lcd public driver 17 bp_ o bp signal output terminals, inverse for lcd display decimal and other special symbols of liquid crystal display driver 22 lb o low battery flag . pull high if low battery 23 v- - negative voltage 24 int - integrator output 25 buf - integration register connection. 26 az - auto-zero capacitor connection 27 inlo i analog low input signal 28 inhi i analog high input signal 29 com - set the common-mode voltage for the system 30 crf- - negative capacitor connection for on-chip a/d converter 31 crf+ - positive capacitor connection for on-chip a/d converter 32 rflo i low differential reference input connection. 33 rfhi i high differential reference input connection 34 hldo keep output terminal display 35 rx - the clock frequency adjustment, through a resistance to v + adjustable reduce chip clock frequency 36 hold hold input pin. connecting to v+ for hold function 37 cap- negative voltage capa citance connection negative terminals 38 gnd i ground 39 cap+ negative voltage capacitance connection positive terminals 40 v+ i positive supply voltage.
m7240 cmos ic unisonic technologies co., ltd 3 of 7 www.unisonic.com.tw qw-r502-682.a ? block diagram lcd phase driver osc 4 logic control v- gen 3-? digital a/d converter low battery detector 7 segment decode 7 segment decode 7 segment decode latch 1000's counter 100's counter 10's counter 1's counter 200 v- to switch drivers v+ cap- gnd cap+ rfhi inhi analog common com inlo rflo lcd driver
m7240 cmos ic unisonic technologies co., ltd 4 of 7 www.unisonic.com.tw qw-r502-682.a ? absolute maximum rating (unless otherwise specified) parameter symbol ratings unit power supply voltage(v+ v- v cc 7 v analog input voltage v iang v+~v- v reference input voltage v iref v+~v- v operating temperature t opr 0 ~ 70 c storage temperature t stg -65 ~ +150 c junction temperature t j 150 c note: absolute maximum ratings are those values be yond which the device could be permanently damaged. absolute maximum ratings are stress ratings only and functional device oper ation is not implied. ? recommended operating conditions ( unless otherwise specified ) parameter symbol min typ max unit power supply voltage v cc 2.5 3 6 v ? electrical characteristics (v cc 3v, t a =25c, unless otherwise specified) parameter symbol test conditions min typ max unit v cc range v cc 2.5 3 6 v supply current (does not conclude common current ) i cc v in =0v 0.2 0.5 ma dc characteristics zero input reading r z v in =0v,full-scale=200mv 0 0 0 digital reading ratio metric reading r r v in =v ref , v ref =100mv 999 1000 1001 digital reading linearity (max deviation form best straight line fit) l full-scale=200.0mv or full-scale=2.0v -1 0.2 +1 counts rollover error e r -v in =+v in ~200mv -1 0.2 +1 counts leakage current input il v ih =0v 1 10 pa low battery flag v+ to v- 2.5 2.6 2.7 v analog common voltage ( with respect to v+ ) v com 25k ? between common and positive supply 2.4 2.5 2.6 v
m7240 cmos ic unisonic technologies co., ltd 5 of 7 www.unisonic.com.tw qw-r502-682.a ? typical applications circuits f1 g1 e1 b2 c2 d2 a2 f2 e2 d3 b3 hldo rx hold cap- gnd cpa+ v+ d1 c1 b1 a1 e3 f3 ab4 pol bp bp- g3 a3 c3 g2 lb v- int buf az inlo inhi com crf- crf+ rflo rfhi m7240 data hold low bat f1 g1 e1 b2 c2 d2 a2 f2 e2 d3 b3 d1 c1 b1 a1 e3 f3 pol bp bp- g3 a3 c3 g2 lb ab4 gnd hd 1m gnd 330 910 25k 3v gnd 0.47uf 0.01uf 1m 0.47uf 0.22uf 100k rj 200 inlo inhi 4.7uf 1uf~4uf j fig.1 note r j is a zero resistance, proper value can eliminate zero salvage value.
m7240 cmos ic unisonic technologies co., ltd 6 of 7 www.unisonic.com.tw qw-r502-682.a ? application information the m7240 is the production of the basic application of lcd digital dc volt age meter and digital multimeter, by selecting different parameters of t he external components, you can creat e different range gauge outfit. the 200mv range gauge outfit which the most widely used because it is three and a half the bas ic components of digital multimeter. as m7240 of 3v low-voltage power supply, making use m7240 production of the digital dc voltage meter input signal can be a total of com and common gnd two a ccess methods, figure 1 is the 200mv typical application circuit. in fig.1 circuit, when moving the jumper j is connected to inlo and com, the compos ition of the input signal connected in com, when moving the jumper j is connected to inlo and gnd, the compos ition of the input signal connected in gnd, for the production of digital multimeter, two input signal c onnection method in general to meet the application requirements. use the com met hod to make the gauge outfit digital multimeter, the circuit is relatively simple form, but because of com client can tolerate a few ma maximum current, the need for greater measurement poured into the current project, not applicable. use the gnd method to make the gauge outfit produced digital multimeter, there is no current problem of affordability, but measurement conv erter circuit is slightly changed. in addition, if you live in the city to use electricity for 60hz, in order to reduce the fr equency of the circuit city electrical effects, the connection between th e rx and power resistors, please use 680k ? . analog common the com pin is used to set the common-mod voltage for t he system in which the input signals are floating with respect to the power supply of the m7240 . in most of the applications, inl o, rflo and com pins are tied to the same point, so that the common mode voltage can be re moved from the reference system and the converter. the com pin is also used as a voltage reference. it sets a voltage of around 2.5 volts more negative than the positive supply. the analog com is tied internally to an nmos capable of sinking 30ma. this nmos will hold the com voltage at 2.5 volts when an external load attempts to pull the com voltage toward the positive supply. the source current of com is only 10 a, so it is easy to pull com voltage to a more negative voltage with respect to the positive supply. reference voltage for a 1000 counts reading, the input signal must be equal to the reference voltage. as a result, it requires the input signal be twice the reference voltage for a 2000 coun ts full-scale reading. thus, for the 200.0mv and 2.000v full-scale, the reference voltage should equal 100.0mv and 1.00 0v, in some applications the full-scale input voltage my be other than 200mv or 2v, but 600mv. for example, the reference voltage should be set to 300mv and the input signal can be used directly without being divided. the differential reference can be used during the measurem ent of resistor by the ratio metric method and when a digital reading of zero is desired for vin 0. a compensating offset voltage c an be applied between com and inlo and the voltage of being measured is connected between com and inhi. auto-zero phase during auto-zero three things happen. first, input high an d low are disconnected from the pins and internally shorted to analog com. second, the refe rence capacitor is charged to the refe rence voltage. third, a feedback loop is closed around the system to charge the auto-zero capacitor c az to compensate for offset voltages in the buffer amplifier, integrator, and comparator. sinc e the comparator is included in the loop , the az accuracy is limited only by the noise of the system. in any case, the o ffset referred to the input is less than 10 v. signal integrate phase during signal integrate phase, the auto- zero loop is opened, the internal short is removed, and the internal input high and low are connected to the external pins. the conver ter then integrates the differ ential voltage between inhi and inlo for a fixed time. this differential voltage can be within a wide common mode range: up to 1v from either supply. if, on the other hand, t he input signal has no return with respect to the converter power supply, inlo can be tied to analog com to establish the correct common mode vo ltage. at the end of this phas e, the polarity of the integrated signal is determined.
m7240 cmos ic unisonic technologies co., ltd 7 of 7 www.unisonic.com.tw qw-r502-682.a ? application information(cont.) differential input the input can accept differential voltages anywhere wi thin the common mode range of the input amplifier, or specifically from 0.5v below the posit ive supply to 1v above the negative suppl y. in this range, the system has a cmrr of 86db typical. however, care must be exercised to assure the integrator output does not saturate. a worst case condition would be a large positive common mode volt age with a near full scale negative differential input voltage. the negative input signal drives the integrator positive when most of its swing has been used up by the positive common mode voltage. for these critical applications t he integrator output swing can be reduced to less than the recommended 2v full scale swing with little loss of accuracy. the integrator output can swing to within 0.3v of either supply without loss of linearity. reference voltage capacitor the reference voltage can be generated anywhere within the power supply voltage of the converter. the main source of common mode error is a roll-over voltage caused by the reference capacitor losing or gaining charge to stray capacity on its nodes. if there is a large common mode voltage, the reference capacitor can gain charge (increase voltage) when called up to de-integrate a positi ve signal but lose charge (decrease voltage) when called up to de-integrate a negative input signal. this difference in refe rence for positive or negative input voltage will give a roll-over error. however, by selecting the reference capacito r such that it is large enou gh in comparison to the stray capacitance, this error can be held to less than 0.5 count worst case. ? component value selection integrating resistor both the buffer amplifier and the integr ator have a class a output stage with 100 a of quiescent current. they can supply 4 a of drive current with negligible nonlinearity. the integrating resistor should be large enough to remain in this very linear region over the input vo ltage range, but small enough that undue leakage requirements are not placed on the pc board. for 2v full scale, 470k ? is near optimum and similarly a 100k ? for a 200mv scale. integrating capacitor the integrating capacitor should be selected to give the maximum voltage swing that ensures tolerance buildup will not saturate the integrator swing(approx imately. 0.3v from either supply).in the m7240 , when the analog common is used as a reference, a nominal+2v full scale int egrator swing is fine. for three readings/second (48khz clock) nominal values for c int are 0.22 f and 0.10 f, respectively. of course, if different oscillator frequencies are used, these values should be changed in inverse proportion to maintain the same output swing. an additional requirement of the integrat ing capacitor is that it must have a low dielectric absorptiont to prevent roll-over errors. while other types of capacitors are adequat e for this application, polypropylene capacitors give undetectable errors at reasonable cost. auto-zero capacitor the size of the auto-zero capacitor has some influenc e on the noise of the system. for 200mv full scale where noise is very important, a 0.47 f capacitor is recommended. on the 2v scale, a 0.047 f capacitor increases the speed of recovery from overload and is adequate for noise on this scale. reference capacitor a 0.1 f capacitor gives good results in most applications. however, where a large common mode voltage exists and a 200mv scale is used, a larger value is r equired to prevent roll-over error. generally 1 f will hold the roll-over error to 0.5 count in this instance. utc assumes no responsibility for equipment failures that result from using products at values that exceed, even momentarily, rated values (such as maximum ratings, operating condition ranges, or other parameters) listed in products specifications of any and all utc products described or contained herein. utc products are not designed for use in life support appliances, devices or systems where malfunction of these products can be reasonably expected to result in personal injury. reproduction in whole or in part is prohibited without the prior written consent of the copyright owner. the information presented in this document does not form part of any quotation or contract, is believed to be accurate and reliable and may be changed without notice.
|
