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1 lt1684 micropower ring tone generator n allows dynamic control of output frequency, cadence, amplitude and dc offset n active tracking supply configuration allows linear generation of ring tone signal n no high voltage post-filtering required n capacitive isolation eliminates optocouplers n low distortion output meets international ptt requirements n differential input signal for noise immunity n user adjustable active output current limit n powered directly from high voltage ringer supplyno additional supplies necessary n supply current: < 1ma n 2% signal amplitude reference n available in 14-pin so and dip packages the lt ? 1684 is a telecommunication ring tone generator. the ic takes a user-generated pulse width modulated (pwm) input and converts it to a high voltage sine wave suitable for telephone ringing applications. the lt1684 receives capacitor-isolated differential pwm input signals encoded with desired ring output cadence, frequency, and amplitude information. the lt1684 nor- malizes the pulse amplitude to 1.25v for an accurate signal voltage reference. the cadence, frequency and amplitude information is extracted using a multiple- pole active filter/amplifier, producing the output ring tone signal. the lt1684 uses its own ring tone output as a reference for generating local supply rails using complementary high voltage external mosfets as dynamic level-shifting devices. this active tracking supply mode of operation allows linear generation of the high voltage ring tone signal, reducing the need for large high voltage filtering elements. n wireless local loop telephones n key system/pbx equipment n fiber to the curb telecom equipment in a gate + in b 6.8nf irf9610 irf610 100k v + p1 m c p2 lim + out bg out at ref comp1 comp2 ampin lim v gate 100pf 1n4001 20pf 100pf 100pf dc isolation pwm controller 100 10k 10k 1n5817 0.1 f 1 f 3k 5k 2k 300k 6.8nf 100k 100 ring tone output 100ma capability 100v + ?00v lt1684 4700pf 1684 ta01 fb1 () fb1: ferronics fmb1601 (716) 388-1020 features descriptio u applicatio s u typical applicatio u , ltc and lt are registered trademarks of linear technology corporation. electrically isolated ring tone generator
2 lt1684 voltages: active tracking differential voltage (gate + C gate C ) ..................................C 0.3v to 42v local supply differential voltage (v + C v C ) ...............................................C 0.3v to 36v local supply voltage v + .............. (gate + C 7.0v) to (gate + + 0.3v) local supply voltage v C .............. (gate C C 0.3v) to (gate C + 7.0v) pwm input differential voltage (in a C in b) .........................................C 7.0v to 7.0v pwm input voltage common mode ................. (v C C 0.3v) to (v + + 0.3v) lim + current limit pin voltage ..................... (out C 0.3v) to (v + + 0.3v) lim C current limit pin voltage .................... (v C C 0.3v) to (out + 0.3v) all other pin voltages ........... (v C C 0.3v) to (v + + 0.3v) currents: lim + , lim C current .......................................... C 350ma out current ....................................................... 350ma bg out current .................................................... 10ma pwm (in a, in b) current .................................... 5ma gate + , gate C current ....................................... 20ma comp1 current .................................................... 1ma comp2 current .................................................... 1ma at ref current ..................................................... 20ma temperatures: operating junction temperature range commercial grade ................................. 0 c to 125 c industrial grade ................................ C 40 c to 125 c storage temperature range ................. C 65 c to 150 c lead temperature (soldering, 10 sec).................. 300 c (note 1) 1 2 3 4 5 6 7 top view n package 14-lead pdip s package 14-lead plastic so 14 13 12 11 10 9 8 in b comp1 comp2 lim v gate at ref in a bg out ampin gate + v + lim + out order part number lt1684cn lt1684cs lt1684in lt1684is t jmax = 125 c, q ja = 75 c/w (n) t jmax = 125 c, q ja = 115 c/w (s) consult factory for military grade parts. absolute axi u rati gs w ww u package/order i for atio uu w
3 lt1684 note 1: absolute maximum ratings are those values beyond which the life of the device may be impaired. note 2: ic supply current specification represents unloaded condition and does not include external fet gate pull up/down currents (gate + , gate C pins). actual total ic bias currents will be higher and vary with operating conditions. see applications information. note 3 : pwm inputs are high impedance through 100mv beyond the input thresholds. note 4: 10k resistor from pin ampin to ground. note 5: guaranteed but not tested. the l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at t a = 25 c. v + C v C = 20v, voltages referenced to pin out, v out = v atref unless otherwise noted. symbol parameter conditions min typ max units supply and protection i s dc supply current (note 2) in a C in b 3 1.6v l 680 950 m a |v + | local supply voltages v gate + 3 v + l 6.5 10 v |v C |v gate C v C v gate + active tracking supply fet i gate + = C100 m a, l 13.2 14.0 14.8 v bias voltage at ref = 0v v gate C active tracking supply fet i gate C = 100 m a, l C14.8 C14.0 C13.2 v bias voltage at ref = 0v pwm receiver f pwm input carrier frequency 10 khz v in minimum valid differential input in a C in b or in b C in a l 1.6 v differential input threshold l 0.50 0.70 1.00 v | in a C in b | r in differential input overdrive impedance v in > v th + 100mv l 710 k w (note 3, 5) r ina,inb single-ended input impedance to pin out l 50 k w (note 5) bg buffer v bgout bg out normalized voltage magnitude |v bgout | 1.235 1.250 1.265 v l 1.225 1.250 1.275 v v bgoutos output offset voltage C7 7 mv [(v bgout +) + (v bgout C)]/2 l C10 10 mv i bgoutsc bg out short-circuit current l 2 4.5 ma r bgout bg out output impedance C 2ma i bgout 2ma 0.2 w t r bg out rise time (10% to 90%) r out = 5k, c out = 10pf l 160 300 ns t f bg out fall time (10% to 90%) r out = 5k, c out = 10pf l 260 400 ns d t r-f bg out risetime C fall time l C 200 C100 0 ns t pr bg out propagation delay pwm input r out = 5k, c out = 10pf l 340 500 ns transition to 10% output (rising edge) t pf bg out propagation delay pwm input r out = 5k, c out = 10pf l 440 600 ns transition to 90% output (falling edge) d t p bg out propagation delay l C 200 C100 100 ns rising edge C falling edge output amplifier v outos out offset voltage v ampin = 0v, i out = 0a C 6 6 mv r ampin = 10k (note 4) l C8 8 mv r out out output impedance C10ma 3 i lim + 3 C100ma, lim + shorted to out 0.01 w 10ma i out 100ma, lim C shorted to v C 0.15 w i outsc out short-circuit current lim + shorted to out l 100 190 ma lim C shorted to v C electrical characteristics
4 lt1684 dc supply current vs v + C v C dc supply current vs temperature v gate C v atref voltage magnitudes vs i gate v + ?v (v) 14 16 18 20 22 24 dc supply current ( a) 1684 g01 740 720 700 680 660 640 620 600 in a ?in b 3 1.6v in a ?in b ?.6v t j = 25 c temperature ( c) 50 25 0 25 50 75 100 125 dc supply current ( m a) 1684 g02 710 690 670 650 630 610 590 570 550 in a ?in b 3 1.6v in a ?in b ?.6v i gate (ma) 0.1 0.3 1.0 3.0 10.0 ? v gate ?v atref ? (v) 1684 g03 14.3 14.2 14.1 14.0 13.9 13.8 t j = 25 c v gate C v atref voltage magnitudes vs temperature pwm input thresholds vs temperature v bgout magnitude vs temperature temperature ( c) ? v gate ?v atref ? (v) 1684 g04 14.5 14.4 14.3 14.2 14.1 14.0 13.9 13.8 13.7 13.6 13.5 50 25 0 25 50 75 100 125 i gate = 1ma temperature ( c) 50 25 0 25 50 75 100 125 ? in a ?in b ? (v) 1684 g05 0.85 0.80 0.75 0.70 0.65 0.60 0.55 0.50 0.45 temperature ( c) 50 25 0 25 50 75 100 125 ? v bgout ? (v) 1684 g06 1.253 1.252 1.251 1.250 1.249 1.248 1.247 1.246 1.245 pwm buffer (pin bg out ) current limit vs temperature output amplifier current limit vs temperature (r lim = 0 w ) output amplifier current limit vs external limiting resistor values temperature ( c) 50 25 0 25 50 75 100 125 pwm buffer current limit (ma) 1684 g07 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 temperature ( c) output current limit (ma) 1684 g08 250 225 200 175 150 125 100 50 25 0 25 50 75 100 125 r lim ( ) 0 2 1 4 6 8 3 5 7 910 output current limit (ma) 1684 g09 200 150 100 50 0 typical (t j = 25 c) minimum (t j = 125 c) typical perfor a ce characteristics uw
5 lt1684 in b (pin 1): pwm negative input. input is isolated from digital source by ~100pf series capacitor. a 10k resistor can be connected to the in b pin in series with the isolation capacitor for transient protection. the pwm receiver imple- ments a diode forward drop of input hysteresis (relative to in a). this hysteresis and internal signal limiting assure common mode glitch rejection with isolation capacitor mismatches up to 2:1. for maximum performance, how- ever, effort should be made to match the two pwm input isolation capacitors. pin in b is differentially clamped to pin in a through back-to-back diodes. this results in a high impedance differential input through 100mv be- yond the input thresholds. 5k internal input resistors yield a 10k (nominal) differential overdrive impedance. comp1 (pin 2): output amplifier primary compensation. connect a 100pf capacitor from pin comp1 to pin out. comp2 (pin 3): output amplifier secondary compensa- tion. connect a 20pf capacitor from pin comp2 to pin out. lim C (pin 4): output amplifier current sink limit. pin implements i out ? r = v be current clamp. internal clamp resistor has a typical value of 3.5 w . for maximum current drive capability (190ma typical) short pin to pin v C . reduction of current sink capability is achieved by placing additional resistance from pin lim C to pin v C . (i.e. an external 3.5 w resistance from pin lim C to pin v C will reduce the current sinking capability of the output ampli- fier by approximately 50%.) v C (pin 5): local negative supply. typically connected to the source of the active tracking supply p-channel mosfet. v C rail voltage is gate C self-bias voltage less the mosfet v gs . typical p-channel mosfet characteristics provide at ref C v C ? 10v. gate C (pin 6): negative power supply fet gate drive. pin sources current from pull-down resistor to bias gate of active tracking supply p-channel mosfet. self-biases to a typical value of C14v, referenced to pin at ref . pull-down resistor value is determined such that current sourced from the gate C pin remains greater than 50 m a at mini- mum output signal voltage and less than 10ma at maxi- mum output signal voltage. at ref (pin 7): active tracking supply reference. typi- cally connected to pin out. pin bias current is the differ- ence between the magnitudes of gate + pin bias and gate C pin bias (i atref = ? i gate + ? C ? i gate C ? ). out (pin 8): ring tone output pin. output of active filter amplifier/buffer. used as reference voltage for internal functions of ic. usually shorted to pin at ref to generate reference for active tracking supply circuitry. connect a 1a (1n4001-type) diode between v + and out and a 1a schottky diode from v C to out for line transient protection. lim + (pin 9): output amplifier current source limit. pin implements i out ? r = v be current clamp. internal clamp resistor has a typical value of 3.5 w . for maximum current drive capability (190ma typical) short pin lim + to pin out. reduction of current source capability is achieved by placing additional resistance from pin lim + to pin out. (i.e. an external 3.5 w resistance from pin lim + to pin out will reduce the current sourcing capability of the output amplifier by approximately 50%.) v + (pin 10): local positive supply. typically connected to the source of the active tracking supply n-channel mosfet. this condition should be made using a ferrite bead. operating v + rail voltage is gate + self-bias voltage less the mosfet v gs . typical n-channel mosfet characteris- tics provide v + C at ref ? 10v. gate + (pin 11): positive power supply fet gate drive. pin sinks current from pull-up resistor to bias gate of active tracking supply n-channel mosfet. self-biases to a typical value of 14v, referenced to pin at ref . pull-up resistor value is determined such that sink current into gate + pin remains greater than 50 m a at maximum output signal voltage and less than 10ma at minimum output signal voltage. ampin (pin 12) : output amplifier input. connected to external filter components through series protection re- sistor (usually 5k). thevenin dc resistance of external filter and protection components should be 10k for opti- mum amplifier offset performance. see applications in- formation section. uu u pi fu ctio s
6 lt1684 bg out (pin 13): normalized pwm buffered output. pwm differential input is amplitude normalized to 1.25v (refer- enced to the out pin). this signal is used to drive the active filter/amplifier. filter resistor values must be chosen to limit the maximum current load on this pin to less than 2ma. the output is current limit protected to a typical value of 4.5ma. in a (pin 14): pwm positive input. input is isolated from digital source by ~100pf series capacitor. a 10k resistor should be connected to the in a pin in series with the isolation capacitor for transient protection. the pwm receiver implements a diode forward drop of input hyster- esis (relative to in b). this hysteresis and internal signal limiting assure common mode glitch rejection with isola- tion capacitor mismatches up to 2:1. for maximum perfor- mance, however, effort should be made to match the two pwm input isolation capacitors. pin in a is differentially clamped to pin in b through back-to back isolation-base diodes. this results in a high impedance differential input 100mv beyond the input thresholds. 5k internal input resistors yield a 10k (nominal) differential overdrive im- pedance. lt1684 block diagram + 5k 10k in a 100pf + 5k 10k in b 100pf pwm input 5k ampin 20pf (ring return) 100pf filter elements bg out comp1 comp2 ring output 15k current limit gate lim v v v + out lim + at ref 14v 14v gate + v + 1684 bd 1.25v 1.25v uu u pi fu ctio s fu n ctio n al block diagra uu w
7 lt1684 basic theory of operation the lt1684 operates using a user-provided pulse-width- modulated (pwm) digital signal as input*. the low fre- quency modulation component of this signal represents the desired output waveform. changing the pwm input can thus dynamically control the frequency, cadence, amplitude and dc offset of the desired output. this method of sine wave generation can accomodate all popular ring tone frequencies including 17hz, 20hz, 25hz and 50hz. the lt1684 receives the pwm input by a capacitor- isolated differential input at pins in a and in b. this signal is amplitude normalized by a bandgap reference and output single-ended on the bg out pin such that the pwm carrier is 1.25v about the voltage on the out pin. the low frequency component of the normalized pwm signal is recovered using an active filter circuit con- structed using an onboard driver amplifier. this amplifier also provides current drive for the final ring tone output. the ring tone output is used as the reference for a floating active biasing scheme by pin at ref . as the ring tone output rises and falls through its typical range of hundreds of volts, the lt1684 tracks the output signal, maintain- ing local supply voltages across the ic of approximately 10v. input receiver/reference buffer the differential receiver for the pwm input signal requires minimum differential input levels of 1.6v to assure valid change-of-state. the receiver inputs are capacitor coupled, isolating the lt1684 from the pwm generator. the re- ceiver is leading edge triggered. the input receiver controls a switched-state output that forces an amplitude normalized voltage (referenced to the out pin) of 1.25v that follows the pwm input. this switched voltage is driven off-chip on pin bg out . when the in a input is driven higher than in b (by the required 1.6v), the reference drives bg out to +1.25v above out. when in b input is driven higher than in a, bg out is forced to C1.25v relative to out. the amplitude normalized representation of the input pwm signal is used as the input for the active filter element and output driver. output amplifier/driver the normalized pwm signal output on the bg out pin is converted to the final ring tone signal by an active filter. this filter consists of an onboard amplifier and a few external components. although many different types of filters can be constructed, a 2-pole multiple feedback (mfb) configuration generally provides adequate perfor- mance and is desirable due to its simplicity and effective- ness. the low frequency component of the 1.25v pwm signal contains the desired ring tone frequency and cadence information. the mfb active filter strips this information from the pwm signal and amplifies this low frequency component to generate the final desired output. active tracking supplies implementation of the active tracking supply technique enables linear generation of the ring tone output, and takes advantage of the intrinsic supply noise immunity of a linear amplifier, reducing the need for large high voltage filtering elements. two external power mosfets act as voltage level-shifting devices and generate the power supply voltages for the lt1684. the lt1684 uses its own output as a voltage reference for the fet level shifters, suspending itself (by these generated supply voltages) about the signal output. in this manner, the lt1684 can linearly generate a signal hundreds of volts in amplitude at its output, while main- taining 10v local supply rails across the ic itself. (refer to functional block diagram) * contact linear technology for code. operatio u
8 lt1684 encoded pwm signal input basics the lt1684 accepts a user-supplied pwm carrier that represents the desired output ring tone signal. this pwm input is normalized by the lt1684 such that ring tone output amplitudes can be accurately encoded into the pwm input. the lt1684 accepts a differential input to maximize rejec- tion of system transients and ground noise. if no differen- tial signal is readily available from the pwm controller, a simple inverter/buffer block can be used to create the differential signal required. each differential input is internally connected through a 5k series resistor to back-to-back isolation-base diodes. these devices internally clamp the differential input signal to 100mv greater than the input comparator hysteresis range. the input comparator toggles with a differential hysteresis equal to that of a standard diode forward voltage (0.7v nominal). as such, the differential imped- ance of the input remains high throughout the input hysteresis region, then reduces to a nominal value of 10k (7k minimum) as the input is overdriven beyond the comparator input threshold. a minimum differential input of 1.6v is specified to assure valid switching. the pwm signal can be visualized in terms of instanta- neous ring tone amplitude, normalized to the lt1684 amplitude reference. for a given desired output voltage v outn , the input pulse train required follows the relation: v outn = 2 ? v ref ? (dc C 0.5), or dc = [v outn / (2 ? v ref )] + 0.5, where: v ref = 1.25v normalized peak voltage dc = pwm input duty cycle a 10% to 90% duty cycle range is a practical limit for a 10khz input carrier. this corresponds to normalized sig- nal amplitude of 1v. duty cycles exceeding this range can cause increased output signal distortion as signal energy is lost due to finite rise and fall times becoming a signifi- cant percentage of the signal pulses. the associated reduction in the pulse energy manifests itself as a soft clipping of the output signal resulting in an increase in harmonic distortion. the normalized pwm signal is amplified to the desired output signal level by the active filter/amplifier stage. thus, dividing the desired peak output amplitude by the peak normalized encoded amplitude (v out /v outn ) yields the required dc gain of the active filter. system considerations assuming use of a 10% to 90% maximum pwm range, the peak normalized signal will be: v pwm (pk) = 0.8 ? v ref = 1.0v, and: v out (pk) = v pwm (pk) ? filter dc gain thus, the dc gain of the output filter equals the desired peak voltage of the output ring tone signal. the frequency characteristics of the lowpass output filter must reflect the allowable carrier ripple on the output signal. for example, a 10khz carrier system could use a 2-pole butterworth lowpass with a cutoff frequency of 100hz. this filter provides 40db of input signal rejection at 10khz yielding 25mv p-p output ripple. if the dc gain of the output filter/amplifier was 100, the output ripple volt- age would be riding on a 100v sine wave, and therefore be about C 78db relative to the output ring signal. applicatio s i for atio wu uu
9 lt1684 for applications that are extremely output ripple sensitive, additional carrier rejection can be accomplished by modi- fying the output filter/amplifier characteristics such as implementing elliptical filter characteristics with a lower cutoff frequency or implementation of additional poles. filter design and component selection the ring tone information represented in the low fre- quency component of the input pwm signal is retrieved using an active filter. this filter also generates the appro- priate low frequency gain required to produce the high voltage output signal and references the output to ground (or other system reference). the frequency and gain characteristics of this circuit element are both configurable by the appropriate choice of external passive filter ele- ments. because of the active tracking supply mode of operation, conventional active filter topologies cannot be used. most amplifier/filter topologies can, however, be transformed into active tracking supply topologies. a conventional amplifier circuit topology can be trans- formed into an active tracking supply amplifier circuit by: a) inverting the amplifier signal polarity (swap amplifier + and C connections) and input source polarity. b) referencing all signals to the output except the feed- back elements, which are referenced to ground (swap output and ground). a variety of amplifier/filter configurations can be realized using the transformation technique. a 2-pole filter is generally adequate for most ringer applications. due to the relative simplicity of infinite-gain multiple feedback (mfb) configurations, these filters are good candidates for ringer applications. component selection and active tracking supply transformation will be described for the following 2-pole mfb infinite-gain lowpass filter. + + v in r1 r2 load + + v in r1 transformation conventional amplifier configuration active tracking supply amplifier lowpass mulitple feedback active filter active tracking supply lowpass multiple feedback filter r2 load transformation + + v in r1 r3 c1 load c2 r2 + r3 r1 1684 f01 load c2 c1 r2 + v in applicatio s i for atio wu uu
10 lt1684 the component selections for the active tracking supply lowpass mfb filter configuration follow the relations: c 2 = mc 1 m 1 / [4q 2 (1+|h o |)] r 2 = 1 [1C4mq 2 (1+|h o |)] 1/2 2 w n c 1 mq r 1 = r 2 / |h o | r 3 =1 w n 2 c 1 2 r 2 m example: conditions: output ring tone peak voltage = 100v ring frequency = 20hz input duty cycle range = 10% to 90% filter q = 0.707 set: f n = w n / 2 p = 100hz choose: c 1 = 1.0 m f (a convenient value) then: m [4(0.7) 2 (1+100)] C1 ? .005 c 2 = mc 1 c2 = 4700pf (sets m = 0.0047) r 2 = 1 [1C 4(0.0047)(0.707) 2 (101)] 1/2 (4 p 100)(1eC6)(.0047)(0.707) r 2 = 300k r 1 = 300k/100 r 1 = 3.0k r 3 = [(2 p 100) 2 (1eC6) 2 (300k)(0.0047)] C1 r 3 = 2k this filter configuration yields a dc gain of 100, a corner frequency of just under 100hz with gain reduction of only 0.1% at 20hz, and a 10khz carrier rejection of greater than 40db at the output. active tracking supply components given the previous discussion, implementation of an active tracking supply system may seem almost trivial. active tracking supply lowpass multiple feedback filter transfer characteristic (a v vs f n ) however, bootstrapping an amplifier system about its own output creates a complex myriad of inherent stability and response issues. attempting such a configuration with generic jelly-bean components is not recommended for the faint of heart or type-a personalities. the lt1684, however, makes for a simplistic approach to active track- ing component selection. the high voltage mosfet transistors used in the circuit must have an operating v ds specified at greater than the corresponding high voltage supply rail plus the opposite maximum excursion of the output signal. for example, if a system is designed with a 240v supply (+ 120v, C120v) and outputs a ring signal that has a 100v peak amplitude, the mosfet v ds ratings must be greater than 240/2 + 100 = 220v. active filter tuned oscillator no pwm input required a simple yet effective method of producing a high quality sine wave is to place a high-q bandpass filter and a hard limited gain element in a positive feedback loop. this circuit will oscillate at the bandpass frequency, producing a sine wave at the filter output. the product of the funda- mental component of the limiter and the filter gain at the bandpass frequency determines the output amplitude. this type of circuit is commonly referred to as an active filter tuned oscillator. hertz (hz) 1 10 100 1k 10k 100k filter gain (db) 1684 f02 ?0 0 50 applicatio s i for atio wu uu
11 lt1684 + r f3 r f1 + r f2 v in c f2 c f1 v out 1684 f4a active filter tuned oscillator block diagram the lt1684 can be implemented easily into a telephone ringer circuit based on the active filter tuned oscillator topology, eliminating the need for a user-supplied pwm input signal. the lt1684s active filter amplifier can be used as a high-q bandpass filter element by configuring it as an active tracking supply bandpass. the lt1684s controlled output receiver/buffer is also convenient for use as the hard limiter. because the lt1684 receiver/ buffer requires a true differential input for proper opera- tion, a dual comparator ic such as the lt1017 must be bootstrapped along with the lt1684 to provide differen- tial control signals. the lt1017 and lt1684 receiver/ buffer combine to create a high gain hard limiter whose output is controlled to 1.25v. the lt1684 active bandpass filter is then connected as a positive feedback element with the limiter component, which completes the active filter tuned oscillator topology. the active bandpass filter circuit is easily configured using a basic mfb bandpass configuration, however, the active tracking supply technique used by the lt1684 requires transformation of this topology. this transformation swaps the amplifier signal polarity, references all signals to the output, and references all feedback elements to ground as described previously in the filter design and component selection section. the design equations for the active tracking bandpass filter are the same as the pretransformation mfb topology, such that if c f1 = c f2 = c: r f1 = q/( w o ? c ? ? h 0 ? ) r f2 = q/(2q 2 C ? h 0 ? )( w o ? c) r f3 = 2q/( w o ? c) example: conditions: output peak voltage = 95v ring frequency = 20hz bandpass q = 9.4 a square wave with peak amplitude a has a fundamental component with amplitude 4a/ p , where a = 1.25v. there- fore, the desired filters bandpass gain ? h o ? = 95/(4 ? 1.25/ p ) ~ 60. given capacitor values c = 0.22 m f (a conve- nient value) and desired filter characteristics of: q = 9.4, ? h o ? = 60, w o = 2 p (20hz), then: r f1 = 5.6k, r f2 = 2.7k, r f3 = 680k. the amplitude, frequency and envelope re- sponse time of the output signal can be adjusted by simply changing the values of resistors r f1 to r f3 accordingly. this produces a high voltage, high quality 20hz sine wave at the filter output with a peak amplitude of 95v. differen- tial amplitude and frequency characteristics are achieved by simply changing a few resistor values. the output of the lt1684 is internally current limited to a minimum of 100ma peak, allowing this ring tone generation circuit to be used with loads up to 7 ren with no degradation of the output waveform. + r f2 + r f1 v in c f2 r f3 c f1 v out 1684 f5b bandpass mfb filter active tracking bandpass mfb filter 1684 f03 applicatio s i for atio wu uu
12 lt1684 in b comp1 comp2 lim v gate at ref in a bg out ampin gate + lt1684 v + lim + out 1 2 3 4 5 6 110v 110v 7 14 13 12 11 10 9 8 r10 10k c2 100pf d1 1n5817 c1 20pf r8 10k r f1 5.6k r3 100k r2 100 fb1 m1 irf610 m2 irf9610 c5 0.1 f d2 1n4001 output 1684 f05a + c4 6.8nf r1 100 r f2 2.7k r4 100k r f3 680k c f1 0.22 f c f2 0.22 f r9 10k r6 1k + 1/2 lt1017 v + 8 7 4 5 6 v + 1/2 lt1017 v + 8 4 3 2 1 v r5 100k c3 6.8nf 100ma peak () fb1: ferronics fmb1601 (716) 388-1020 active filter tuned oscillator ring tone generator ringer output applicatio s i for atio wu uu
13 lt1684 5v-15v to ring tone fully isolated converter using an active filter-tuned oscillator circuit in b comp1 comp2 lim v gate at ref in a bg out ampin gate + lt1684 v + lim + out 1 2 3 4 5 6 7 14 13 12 11 10 9 8 c6 100pf ds1 1n5817 c5 20pf r3 10k r f1 5.6k r8 100k r1 1k r2 10k r7 100k r4 10k lt1017 r6 100 fb1 m1 irf610 m2 irf9610 c3 0.1 f d1 1n4001 output 1684 ta03 + c2 6.8nf r5 100 ds2 mbrs1100 r f2 2.7k r14 100k r f3 680k c f1 0.22 f c f2 0.22 f c1 6.8nf out a ?n a +in a v ee 8 7 6 5 1 2 3 4 v cc out b in b +in b r13 50k dz4 91v opto2 h11ag1 1 5 4 6 2 4 1 3 5 2 r11 50k r10 10k 2 5, 6 7, 8 1 12 11 4 9 r15 2k v in fb sw lt1270 gnd v c c10 0.1 f c13 0.01 f c4 1 f c8 1nf r12 10k r9 39 d3 1n4001 t1 coiltronics 14239-x3 c9 0.47 f 160v c11 0.47 f 160v c14 10 f 160v c15 10 f 160v c12 0.47 f 160v d4 murs160 d2 murs160 dz2 91v opto1 h11ag1 1 5 4 6 2 dz1 44v + + c7 220 f 10v 5v to 15v input + load (ren) 7 10 v (peak) 95v 70v r f1 5.6k 6.8k r f2 2.7k 3.3k r f3 680k 620k fb1: ferronics fmb1601 (716) 388-1020 typical applicatio s u
14 lt1684 pwm in 1000pf 1000pf 10k 10k 3k 300k 0.1 f 470pf 5k 2k 100k 100k 6800pf 6800pf mtp- 2n50e mtp- 2n50e 120v ?20v 100 100 in a in b bg out ampin v + comp1 lim + out at ref comp2 lim v gate + gate 14 1 13 12 10 2 9 8 7 3 4 5 11 6 lt1684 fb1 100pf 20pf 180 h 180 h 3.9k 1nf 1684 ta04 1nf 2n3904 2n3906 2n3906 2n3904 100 47 47 100 100 irf9240 ?00v 1k 1k 1 f 1 f 0.22 0.22 0.22 irf230 100v 2k 1 h v in sense + i lim + v out i lim sense v bottom v top lt1166 2 4 1 8 7 3 6 5 typical power slice (1 of 13 in parallel) 100 fb1: ferronics fmb1601 (716) 388-1020 5kw load 5kw pwm-to-analog converter typical applicatio s u
15 lt1684 dimensions in inches (millimeters) unless otherwise noted. n package 14-lead pdip (narrow 0.300) (ltc dwg # 05-08-1510) s package 14-lead plastic small outline (narrow 0.150) (ltc dwg # 05-08-1610) n14 1098 0.020 (0.508) min 0.125 (3.175) min 0.130 0.005 (3.302 0.127) 0.045 ?0.065 (1.143 ?1.651) 0.065 (1.651) typ 0.018 0.003 (0.457 0.076) 0.100 (2.54) bsc 0.005 (0.125) min 0.255 0.015* (6.477 0.381) 0.770* (19.558) max 3 1 2 4 5 6 7 8 9 10 11 12 13 14 0.009 ?0.015 (0.229 ?0.381) 0.300 ?0.325 (7.620 ?8.255) 0.325 +0.035 0.015 +0.889 0.381 8.255 () *these dimensions do not include mold flash or protrusions. mold flash or protrusions shall not exceed 0.010 inch (0.254mm) 1 2 3 4 0.150 ?0.157** (3.810 ?3.988) 14 13 0.337 ?0.344* (8.560 ?8.738) 0.228 ?0.244 (5.791 ?6.197) 12 11 10 9 5 6 7 8 0.016 ?0.050 (0.406 ?1.270) 0.010 ?0.020 (0.254 ?0.508) 45 0 ?8 typ 0.008 ?0.010 (0.203 ?0.254) s14 1298 0.053 ?0.069 (1.346 ?1.752) 0.014 ?0.019 (0.355 ?0.483) typ 0.004 ?0.010 (0.101 ?0.254) 0.050 (1.270) bsc dimension does not include mold flash. mold flash shall not exceed 0.006" (0.152mm) per side dimension does not include interlead flash. interlead flash shall not exceed 0.010" (0.254mm) per side * ** information furnished by linear technology corporation is believed to be accurate and reliable. however, no responsibility is assumed for its use. linear technology corporation makes no represen- tation that the interconnection of its circuits as described herein will not infringe on existing patent rights. u package descriptio
16 lt1684 1684f lt/tp 0300 4k ? printed in usa ? linear technology corporation 1999 linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 (408) 432-1900 l fax: (408) 434-0507 l www.linear-tech.com typical applicatio u 5v input nonisolated 5 ren ring generator in b c1 100pf c2 100pf pwm input + v in 5v r4 10k lt1684 comp1 comp2 lim v gate at ref in a bg out ampin gate + v + lim + out c3 100pf c4 20pf r2 10k r3 5k fb1 c8 1 f c13 0.1 f r1 2k c5 4700pf c7 6.8nf 160v c6 6.8nf 160v r6 3k d1 1n4001 ds2 d1n5817 ds1 mbrs1100 dz1 60v mmsz5264bt1 ?00v 100v r5 300k r10 100k m2 irf9610 r7 100 r9 100k r8 100 m1 irf610 c11 0.47 f 160v c10 0.47 f 160v t1 coiltronics ctx 14468-x1 12 10 9 7 4, 5 1, 2 + + c12 220 f 35v + d2 murs160t3 d3 murs160t3 v in fb sw v c lt1271 u1 gnd 4 1 5 2 3 v cc +in b out a v ee lt1211 1 4 8 out b ?n a 27 ?n b +in a 36 5 c9 0.1 f r11 470 r12 5k d4 d1n4148 d5 d1n4148 r15 12k r16 1m r13 12k r14 1m ring tone out 1684 ta02 fb1: ferronics fmb1601 (716) 388-1020 related parts part number description comments lt1082 1a high voltage switching regulator v in = 3v to 75v, sw voltage = 100v lt1166 power output stage automatic bias system sets class ab bias currents, eliminates adjustments and thermal runaway ltc1177-5/ltc1177-12 isolated mosfet drivers 2500v rms isolation, ul recognized lt1270 8a power switching regulator v in = 3.5v to 30v, i q = 7ma lt1271 4a power switching regulator v in = 3.5v to 30v, i q = 7ma lt1339 high power synchronous dc/dc controller operation up to 60v, output current up to 50a lt1676 wide input range, high efficiency, step-down switching regulator operation up to 60v, 100khz, up to 500ma output

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