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lt6600-15 1 660015fb typical application description very low noise, differential ampli er and 15mhz lowpass filter the lt ? 6600-15 combines a fully differential ampli? er with a 4th order 15mhz lowpass ? lter approximating a chebyshev frequency response. most differential ampli? ers require many precision external components to tailor gain and bandwidth. in contrast, with the lt6600-15, two external resistors program differential gain, and the ? lters 15mhz cutoff frequency and passband ripple are internally set. the lt6600-15 also provides the necessary level shifting to set its output common mode voltage to accommodate the reference voltage requirements of a/ds. using a proprietary internal architecture, the lt6600-15 integrates an antialiasing ? lter and a differential ampli? er/ driver without compromising distortion or low noise perfor- mance. at unity gain the measured in band signal-to-noise ratio is an impressive 76db. at higher gains the input referred noise decreases so the part can process smaller input differential signals without signi? cantly degrading the output signal-to-noise ratio. the lt6600-15 also features low voltage operation. the differential design provides outstanding performance for a 2v p-p signal level while the part operates with a single 3v supply. the lt6600-15 is packaged in an so-8 and is pin compat- ible with standalone differential ampli? ers. an 8192 point fft spectrum l , lt, ltc and ltm are registered trademarks of linear technology corporation. all other trademarks are the property of their respective owners. features applications n programmable differential gain via two external resistors n adjustable output common mode voltage n operates and speci? ed with 3v, 5v, 5v supplies n 0.5db ripple 4th order lowpass filter with 15mhz cutoff n 76db s/n with 3v supply and 2v p-p output n low distortion, 2v p-p , 800 load, v s = 3v 1mhz: 86dbc 2nd, 90dbc 3rd 10mhz: 63dbc 2nd, 69dbc 3rd n fully differential inputs and outputs n compatible with popular differential ampli? er pinouts n so-8 package n high speed adc antialiasing and dac smoothing in networking or cellular base station applications n high speed test and measurement equipment n medical imaging n drop-in replacement for differential ampli? ers C + C + r in 536 r in 536 0.01f 0.1f 25 25 5.6pf 3v 3v C + v mid v ocm v in v cm a in v + v C d out lt6600-15 ltc2249 3 4 1 7 2 8 5 6 660015 ta01a gain = 536/r in 2.2f 5.6pf 5.6pf frequency (mhz) 0 amplitude (db) C60 C30 C20 40 660015 ta01b C70 C80 C120 10 20 30 C100 0 C10 C40 C50 C90 C110 input 10.7mhz 2v p-p f sample = 80mhz
lt6600-15 2 660015fb pin configuration absolute maximum ratings total supply voltage .................................................11v input current (note 8) ..........................................10ma operating temperature range (note 6).... ?40c to 85c speci? ed temperature range (note 7) .... ?40c to 85c junction temperature ........................................... 150c storage temperature range ...................? 65c to 150c lead temperature (soldering, 10 sec) .................. 300c (note 1) top view in + v mid v ? out ? in ? v ocm v + out + s8 package 8-lead plastic so 1 2 3 4 8 7 6 5 t jmax = 150c, = = = = = = ( ) = = ( ) = = ( ) = = ( ) = = ( ) = = ( ) = = = = = ( ) = = ( ) = = ( ) = = ( ) = = ( ) = = ( ) = = = = = = = = = = = = = = = ( + = = ) = =
lt6600-15 3 660015fb electrical characteristics note 1: stresses beyond those listed under absolute maximum ratings may cause permanent damage to the device. exposure to any absolute maximum rating condition for extended periods may affect device reliability and lifetime. note 2: this is the temperature coef? cient of the internal feedback resistors assuming a temperature independent external resistor (r in ). note 3: the input common mode voltage is the average of the voltages applied to the external resistors (r in ). speci? cation guaranteed for r in 100. note 4: distortion is measured differentially using a differential stimulus, the input common mode voltage, the voltage at pin 2, and the voltage at pin 7 are equal to one half of the total power supply voltage. the l denotes the speci? cations which apply over the full operating temperature range, otherwise speci? cations are at t a = 25c. unless otherwise speci? ed v s = 5v (v + = 5v, v C = 0v), r in = 536 , and r load = 1k. parameter conditions min typ max units filter gain temperature coef? cient (note 2) f in = 250khz, v in = 2v p-p 780 ppm/c noise noise bw = 10khz to 15mhz 109 v rms distortion (note 4) 1mhz, 2v p-p , r l = 800, v s = 3v 2nd harmonic 3rd harmonic 86 90 dbc dbc 10mhz, 2v p-p , r l = 800, v s = 3v 2nd harmonic 3rd harmonic 63 69 dbc dbc differential output swing measured between pins 4 and 5 v s = 5v v s = 3v 3.80 3.75 4.75 4.50 v p-p diff v p-p diff input bias current average of pin 1 and pin 8 C 90 C 35 a input referred differential offset r in = 536 v s = 3v v s = 5v v s = 5v 5 10 10 25 30 35 mv mv mv r in = 133 v s = 3v v s = 5v v s = 5v 5 5 5 15 17 20 mv mv mv differential offset drift 10 v/c input common mode voltage (note 3) differential input = 500mv p-p , v s = 3v r in = 133 v s = 5v v s = 5v 0.0 0.0 C2.5 1.5 3.0 1.0 v v v output common mode voltage (note 5) differential input = 2v p-p , v s = 3v pin 7 = open v s = 5v common mode voltage at pin 2 v s = 5v 1.0 1.5 C1.0 1.5 3.0 2.0 v v v output common mode offset (with respect to pin 2) v s = 3v v s = 5v v s = 5v C35 C40 C55 5 0 C10 40 40 35 mv mv mv common mode rejection ratio 64 db voltage at v mid (pin 7) v s = 5v v s = 3v l 2.45 2.50 1.50 2.55 v v v mid input resistance l 4.3 5.7 7.7 k v ocm bias current v ocm = v mid = v s /2 v s = 5v v s = 3v C10 C10 C2 C2 a a power supply current v s = 3v, v s = 5v v s = 3v v s = 5v v s = 5v 35 38 39 44 45 48 ma ma ma ma power supply voltage l 311v note 5: output common mode voltage is the average of the voltages at pins 4 and 5. the output common mode voltage is equal to the voltage applied to pin 2. note 6: the lt6600c-15 is guaranteed functional over the operating temperature range C40c to 85c. note 7: the lt6600c-15 is guaranteed to meet 0c to 70c speci? cations and is designed, characterized and expected to meet the extended temperature limits, but is not tested at C40c and 85c. the lt6600i-15 is guaranteed to meet speci? ed performance from C40c to 85c. note 8: the inputs are protected by back-to-back diodes. if the differential input voltage exceeds 1.4v, the input current should be limited to less than 10ma.
lt6600-15 4 660015fb typical performance characteristics passband gain and delay output impedance common mode rejection ratio power supply rejection ratio distortion vs frequency amplitude response passband gain and phase passband gain and delay frequency (mhz) 0.1 C20 gain (db) C10 0 10 1 10 100 660015 g01 C30 C40 C50 C60 v s = 5v gain = 1 t a = 25c frequency (mhz) 0 gain (db) phase (deg) C3 C1 1 20 660015 g02 C5 C7 C4 C2 0 C6 C8 C9 45 135 225 C45 C135 0 90 180 C90 C180 C225 5 10 15 25 v s = 5v gain = 1 t a = 25c gain phase frequency (mhz) 0 gain (db) delay (ns) C3 C1 1 20 660015 g03 C5 C7 C4 C2 0 C6 C8 C9 30 40 50 20 10 25 35 45 15 5 0 5 10 15 25 v s = 5v gain = 1 t a = 25c gain delay frequency (mhz) 0 gain (db) delay (ns) 6 10 14 20 660015 g04 2 C2 4 8 12 0 C4 C6 30 40 50 20 10 25 35 45 15 5 0 5 10 15 25 v s = 5v gain = 4 t a = 25c gain delay frequency (mhz) 1 output impedance () 10 0.1 10 100 660015 g05 0.1 1 100 v s = 5v gain = 1 t a = 25c frequency (mhz) 0.1 cmrr (db) 60 70 80 1 10 100 660015 g06 50 40 30 65 75 55 45 35 v in = 1v p-p v s = 5v gain = 1 t a = 25c frequency (mhz) 0.1 50 psrr (db) 60 70 80 1 10 100 600015 g07 40 30 20 10 0 v s = 3v v in = 200mv p-p t a = 25c v + to diffout frequency (mhz) 0.1 C100 C110 distortion (db) C60 C50 1 10 100 660015 g08 C70 C80 C90 differential input, 2nd harmonic differential input, 3rd harmonic single-ended input, 2nd harmonic single-ended input, 3rd harmonic v in = 2v p-p v s = 3v r l = 800 at each output gain = 1 t a = 25c
lt6600-15 5 660015fb typical performance characteristics distortion vs output common mode total supply current vs total supply voltage transient response distortion vs signal level distortion vs input common mode level distortion vs input common mode level distortion vs signal level input level (v p-p ) 0 C60 C50 C40 4 660015 g09 C70 C80 123 5 C90 C100 C110 distortion (db) v s = 3v r l = 800 at each output gain = 1 t a = 25c 2nd harmonic 10mhz input 2nd harmonic 1mhz input 3rd harmonic 10mhz input 3rd harmonic 1mhz input input level (v p-p ) 0 C60 C50 C40 4 660015 g10 C70 C80 123 5 C90 C100 C110 distortion (db) v s = 5v r l = 800 at each output gain = 1 t a = 25c 2nd harmonic, 10mhz input 3rd harmonic, 10mhz input 2nd harmonic, 1mhz input 3rd harmonic, 1mhz input input common mode voltage relative to pin 7 (v) C3 C110 C100 distortion component (db) C90 C80 C70 C60 C50 C40 C2 C1 0 1 2 660015 g11 3 2nd harmonic, v s = 3v 3rd harmonic, v s = 3v 2nd harmonic, v s = 5v 3rd harmonic, v s = 5v gain = 1 r l = 800 at each output t a = 25c 2v p-p 1mhz input input common mode voltage relative to pin 7 (v) C3 C100 distortion component (db) C90 C80 C70 C60 C50 C40 C2 C1 0 1 2 660015 g12 3 gain = 4, r l = 800 at each output t a = 25c, 500mv p-p 1mhz input 2nd harmonic, v s = 3v 3rd harmonic, v s = 3v 2nd harmonic, v s = 5v 3rd harmonic, v s = 5v voltage pin 2 to pin 7 (v) distortion component (db) C70 C60 C50 0.5 1 1.5 660015 g13 C80 C90 C1.5 C1 C0.5 0 2 2.5 C100 C110 C40 2v p-p 1mhz input gain = 1, r l = 800 at each output t a = 25c 2nd harmonic, v s = 3v 3rd harmonic, v s = 3v 2nd harmonic, v s = 5v 3rd harmonic, v s = 5v 2nd harmonic, v s = 5v 3rd harmonic, v s = 5v total supply voltage (v) 20 total supply current (ma) 30 40 50 25 35 45 2468 660015 g14 10 12 t a = C40c t a = 25c t a = 85c out C 200mv/div in + 500mv/div in C 100ns/div differential gain = 1 single-ended input differential output 660015 g15 out + 200mv/div
lt6600-15 6 660015fb pin functions in C and in + (pins 1, 8): input pins. signals can be ap- plied to either or both input pins through identical external resistors, r in . the dc gain from differential inputs to the differential outputs is 536/r in . v ocm (pin 2): is the dc common mode reference voltage for the 2nd filter stage. its value programs the common mode voltage of the differential output of the ? lter. pin 2 is a high impedance input, which can be driven from an external voltage reference, or pin 2 can be tied to pin 7 on the pc board. pin 2 should be bypassed with a 0.01f ceramic capacitor unless it is connected to a ground plane. v + and v C (pins 3, 6): power supply pins . for a single 3.3v or 5v supply (pin 6 grounded) a quality 0.1f ceramic bypass capacitor is required from the positive supply pin (pin 3) to the negative supply pin (pin 6). the bypass should be as close as possible to the ic. for dual supply applications, bypass pin 3 to ground and pin 6 to ground with a quality 0.1f ceramic capacitor. out + and out C (pins 4, 5): output pins . pins 4 and 5 are the ? lter differential outputs. each pin can drive a 100 and/or 50pf load. v mid (pin 7): the v mid pin is internally biased at mid- supply, see the block diagram section. for single supply operation, the v mid pin should be bypassed with a qual- ity 0.01f ceramic capacitor to pin 6. for dual supply operation, pin 7 can be bypassed or connected to a high quality dc ground. a ground plane should be used. a poor ground will increase noise and distortion. pin 7 sets the output common mode voltage of the 1st stage of the ? lter. it has a 5.5k impedance, and it can be overridden with an external low impedance voltage source. block diagram C + C + v ocm C C + + v ocm 536 536 200 200 200 200 1 2 3 4 v + v C 11k 11k 8 7 6 5 op amp proprietary lowpass filter stage v in C v in + r in r in 660015 bd in + v ocm v + out + out C v C v mid in C
lt6600-15 7 660015fb applications information interfacing to the lt6600-15 the lt6600-15 requires two equal external resistors, r in , to set the differential gain to 536/r in . the inputs to the ? lter are the voltages v in + and v in C presented to these external components, figure 1. the difference between v in + and v in C is the differential input voltage. the aver- age of v in + and v in C is the common mode input voltage. similarly, the voltages v out + and v out C appearing at pins 4 and 5 of the lt6600-15 are the ? lter outputs. the differ- ence between v out + and v out C is the differential output voltage. the average of v out + and v out C is the common mode output voltage. figure 1 illustrates the lt6600-15 operating with a single 3.3v supply and unity passband gain; the input signal is dc coupled. the common mode input voltage is 0.5v, and the differential input voltage is 2v p-p . the common mode output voltage is 1.65v, and the differential output voltage is 2v p-p for frequencies below 15mhz. the common mode output voltage is determined by the voltage at pin 2. since pin 2 is shorted to pin 7, the output common mode is the mid-supply voltage. in addition, the common mode input voltage can be equal to the mid-supply voltage of pin 7 (see the distortion vs input common mode level graphs in the typical performance characteristics section). figure 2 shows how to ac couple signals into the lt6600-15. in this instance, the input is a single-ended signal. ac coupling allows the processing of single-ended or differential signals with arbitrary common mode levels. the 0.1f coupling capacitor and the 536 gain setting resistor form a high pass ? lter, attenuating signals below 3khz. larger values of coupling capacitors will proportion- ally reduce this highpass 3db frequency. figure 1 figure 2 figure 3 C + 536 536 0.01f 0.1f 3.3v C + v in C v in + 3 4 1 7 2 8 5 6 660015 f01 v out + v out C v t 3 2 1 v in + v in C v t 3 2 1 v out + lt6600-15 v out C 0 0 C + 536 536 0.01f 0.1f 0.1f 0.1f 3.3v C + v in + 3 4 1 7 2 8 5 6 660015 f02 v out + v out C v 3 2 1 0 lt6600-15 v out + v out C 2 v t 1 0 C1 v in + C + 133 133 0.1f 0.01f 5v C + v in C v in + 3 4 1 7 2 8 5 6 660015 f03 v out + v out C 62pf 62pf + C 2v v t 3 2 1 0 v out + v out C lt6600-15 v t 3 2 1 0 v in + v in C 500mv p-p (diff)
lt6600-15 8 660015fb applications information in figure 3 the lt6600-15 is providing 12db of gain. the gain resistor has an optional 62pf in parallel to improve the passband ? atness near 15mhz. the common mode output voltage is set to 2v. use figure 4 to determine the interface between the lt6600-15 and a current output dac. the gain, or tran- simpedance, is de? ned as a = v out /i in . to compute the transimpedance, use the following equation: a = 536 ? r1 r1 + r2 () () by setting r1 + r2 = 536, the gain equation reduces to a = r1(). the voltage at the pins of the dac is determined by r1, r2, the voltage on pin 7 and the dac output current. consider figure 4 with r1 = 49.9 and r2 = 487. the voltage at pin 7 is 1.65v. the voltage at the dac pins is given by: v dac = v pin7 ? r1 r1 + r2 + 536 + i in ? r1? r2 r1 + r2 = 77mv + i in ? 45.3 i in is i in + or i in C . the transimpedance in this example is 49.8. evaluating the lt6600-15 the low impedance levels and high frequency operation of the lt6600-15 require some attention to the matching networks between the lt6600-15 and other devices. the previous examples assume an ideal (0) source impedance and a large (1k) load resistance. among practical ex- amples where impedance must be considered is the evalu- ation of the lt6600-15 with a network analyzer. figure 5 is a laboratory setup that can be used to characterize the lt6600-15 using single-ended instruments with 50 source impedance and 50 input impedance. for a unity gain con? guration the lt6600-15 requires a 536 source resistance yet the network analyzer output is calibrated for a 50 load resistance. the 1:1 transformer, 52.3 and 523 resistors satisfy the two constraints above. the transformer converts the single-ended source into a differential stimulus. similarly, the output of the lt6600-15 will have lower distortion with larger load resistance yet the analyzer input is typically 50. the 4:1 turns (16:1 impedance) transformer and the two 402 resistors of figure 5, present the output of the lt6600-15 with a 1600 differential load, or the equivalent of 800 to ground at each output. the impedance seen by the network analyzer input is still 50, reducing re? ections in the cabling be- tween the transformer and analyzer input. differential and common mode voltage ranges the differential ampli? ers inside the lt6600-15 contain circuitry to limit the maximum peak-to-peak differential voltage through the ? lter. this limiting function prevents excessive power dissipation in the internal circuitry and provides output short-circuit protection. the limiting function begins to take effect at output signal levels above 2v p-p and it becomes noticeable above 3.5v p-p . this is illustrated in figure 6; the lt6600-15 was con? gured with unity passband gain and the input of the ? lter was driven with a 1mhz signal. because this voltage limiting takes place well before the output stage of the ? lter reaches the figure 4 figure 5 C + 0.1f 3.3v C + lt6600-15 3 4 1 0.011f current output dac 7 2 8 5 v out + v out C 660015 f04 6 r2 r1 i in C i in + r2 r1 C + 0.1f 0.1f 2.5v C2.5v C + lt6600-15 3 4 1 7 2 8 5 6 660015 f05 402 402 network analyzer input 50 coilcraft ttwb-16a 4:1 network analyzer source coilcraft ttwb-1010 1:1 50 52.3 523 523
lt6600-15 9 660015fb applications information supply rails, the input/output behavior of the ic shown in figure 6 is relatively independent of the power supply voltage. the two ampli? ers inside the lt6600-15 have indepen- dent control of their output common mode voltage (see the block diagram section). the following guidelines will optimize the performance of the ? lter. pin 7 must be bypassed to an ac ground with a 0.01f or larger capacitor. pin 7 can be driven from a low impedance source, provided it remains at least 1.5v above v C and at least 1.5v below v + . an internal resistor divider sets the voltage of pin 7. while the internal 11k resistors are well matched, their absolute value can vary by 20%. this should be taken into consideration when connecting an external resistor network to alter the voltage of pin 7. pin 2 can be shorted to pin 7 for simplicity. if a different common mode output voltage is required, connect pin 2 to a voltage source or resistor network. for 3v and 3.3v supplies the voltage at pin 2 must be less than or equal to the mid supply level. for example, voltage (pin 2) 1.65v on a single 3.3v supply. for power supply voltages higher than 3.3v the voltage at pin 2 should be within the voltage of pin 7 C 1v to the voltage of pin 7 + 2v. pin 2 is a high impedance input. the lt6600-15 was designed to process a variety of input signals including signals centered around the mid-sup- ply voltage and signals that swing between ground and a positive voltage in a single supply system (figure 1). the range of allowable input common mode voltage (the average of v in + and v in C in figure 1) is determined by the power supply level and gain setting (see distortion vs input common mode level in the typical performance characteristics section). common mode dc currents in applications like figure 1 and figure 3 where the lt6600-15 not only provides lowpass ? ltering but also level shifts the common mode voltage of the input signal, dc currents will be generated through the dc path between input and output terminals. minimize these currents to decrease power dissipation and distortion. consider the application in figure 3. pin 7 sets the output common mode voltage of the 1st differential ampli? er inside the lt6600-15 (see the block diagram section) at 2.5v. since the input common mode voltage is near 0v, there will be approximately a total of 2.5v drop across the series combination of the internal 536 feedback resistor and the external 133 input resistor. the resulting 3.7ma common mode dc current in each input path, must be absorbed by the sources v in + and v in C . pin 2 sets the common mode output voltage of the 2nd differential ampli? er inside the lt6600-15, and therefore sets the common mode output voltage of the ? lter. since, in the example of figure 3, pin 2 differs from pin 7 by 0.5v, an additional 2.5ma (1.25ma per side) of dc current will ? ow in the resistors coupling the 1st differential ampli? er output stage to ? lter output. thus, a total of 9.9ma is used to translate the common mode voltages. a simple modi? cation to figure 3 will reduce the dc com- mon mode currents by 40%. if pin 7 is shorted to pin 2 the common mode output voltage of both op amp stages will be 2v and the resulting dc current will be 6ma. of course, by ac coupling the inputs of figure 3, the common mode dc current can be reduced to 2.5ma. figure 6. output level vs input level, differential 1mhz input, gain = 1 1mhz input level (v p-p ) 0 20 0 C20 C40 C60 C80 C100 35 660015 f06 12 467 output level (dbv) 3rd harmonic 85c 1db compression points 25c 85c 3rd harmonic 25c 2nd harmonic, 25c 2nd harmonic 85c
lt6600-15 10 660015fb applications information noise the noise performance of the lt6600-15 can be evaluated with the circuit of figure 7. given the low noise output of the lt6600-15 and the 6db attenuation of the transformer coupling network, it is necessary to measure the noise ? oor of the spectrum analyzer and subtract the instrument noise from the ? lter noise measurement. example: with the ic removed and the 25 resistors grounded, figure 7, measure the total integrated noise (e s ) of the spectrum analyzer from 10khz to 15mhz. with the ic inserted, the signal source (v in ) disconnected, and the input resistors grounded, measure the total integrated noise out of the ? lter (e o ). with the signal source connected, set the frequency to 1mhz and adjust the amplitude until v in measures 100mv p-p . measure the output amplitude, v out , and compute the passband gain a = v out /v in . now compute the input referred integrated noise (e in ) as: e in = (e o ) 2 ?(e s ) 2 a table 1 lists the typical input referred integrated noise for various values of r in . figure 8 is plot of the noise spectral density as a func- tion of frequency for an lt6600-15 using the ? xture of figure 7 (the instrument noise has been subtracted from the results). table 1. noise performance passband gain (v/v) r in input referred integrated noise 10khz to 15mhz input referred integrated noise 10khz to 30mhz 4 133 36v rms 51v rms 2 267 62v rms 92v rms 1 536 109v rms 169v rms the noise at each output is comprised of a differential component and a common mode component. using a transformer or combiner to convert the differential outputs to single-ended signal rejects the common mode noise and gives a true measure of the s/n achievable in the system. conversely, if each output is measured individually and the noise power added together, the resulting calculated noise level will be higher than the true differential noise. power dissipation the lt6600-15 ampli? ers combine high speed with large- signal currents in a small package. there is a need to ensure that the die junction temperature does not exceed 150c. the lt6600-15 package has pin 6 fused to the lead frame to enhance thermal conduction when connect- ing to a ground plane or a large metal trace. metal trace and plated through-holes can be used to spread the heat generated by the device to the backside of the pc board. for example, on a 3/32" fr-4 board with 2oz copper, a total of 660 square millimeters connected to pin 6 of the lt6600-15 (330 square millimeters on each side of the pc board) will result in a thermal resistance, ja , of about 85c/w. without the extra metal trace connected to the v C pin to provide a heat sink, the thermal resistance will be around 105c/w. table 2 can be used as a guide when considering thermal resistance. figure 7 figure 8. input referred noise, gain = 1 C + 0.1f 0.1f 2.5v C2.5v C + lt6600-15 3 4 1 7 2 8 5 6 r in r in 25 25 660015 f07 spectrum analyzer input 50 v in coilcraft ttwb-1010 1:1 frequency (mhz) 10 noise density (nv rms / hz ) integrated noise (v) 20 25 35 45 40 0.01 1 10 100 660015 f08 0 0.1 30 15 5 40 80 100 140 180 160 0 120 60 20 noise density, gain = 1x noise density, gain = 4x integrated noise, gain = 1x integrated noise, gain = 4x
lt6600-15 11 660015fb 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 representa- tion that the interconnection of its circuits as described herein will not infringe on existing patent rights. s8 package 8-lead plastic small outline (narrow .150 inch) (reference ltc dwg # 05-08-1610) applications information table 2. lt6600-15 so-8 package thermal resistance copper area topside (mm 2 ) backside (mm 2 ) board area (mm 2 ) thermal resistance (junction-to-ambient) 1100 1100 2500 65c/w 330 330 2500 85c/w 35 35 2500 95c/w 35 0 2500 100c/w 0 0 2500 105c/w junction temperature, t j , is calculated from the ambient temperature, t a , and power dissipation, p d . the power dissipation is the product of supply voltage, v s , and supply current, i s . therefore, the junction temperature is given by: t j = t a + (p d ? ja ) = t a + (v s ? i s ? ja ) where the supply current, i s , is a function of signal level, load impedance, temperature and common mode voltages. for a given supply voltage, the worst-case power dissi- pation occurs when the differential input signal is maxi- mum, the common mode currents are maximum (see the applications information section regarding common mode dc currents), the load impedance is small and the ambient temperature is maximum. to compute the junc- tion temperature, measure the supply current under these worst-case conditions, estimate the thermal resistance from table 2, then apply the equation for t j . for example, using the circuit in figure 3 with a dc differential input voltage of 250mv, a differential output voltage of 1v, no load resistance and an ambient temperature of 85c, the supply current (current into pin 3) measures 50ma. as- suming a pc board layout with a 35mm 2 copper trace, the ja is 100c/w. the resulting junction temperature is: t j = t a + (p d ? ja ) = 85 + (5 ? 0.05 ? 100) = 110c when using higher supply voltages or when driving small impedances, more copper may be necessary to keep t j below 150c. package description .016 ? .050 (0.406 ? 1.270) .010 ? .020 (0.254 ? 0.508) 45 0 ? 8 typ .008 ? .010 (0.203 ? 0.254) so8 0303 .053 ? .069 (1.346 ? 1.752) .014 ? .019 (0.355 ? 0.483) typ .004 ? .010 (0.101 ? 0.254) .050 (1.270) bsc 1 2 3 4 .150 ? .157 (3.810 ? 3.988) note 3 8 7 6 5 .189 ? .197 (4.801 ? 5.004) note 3 .228 ? .244 (5.791 ? 6.197) .245 min .160 .005 recommended solder pad layout .045 .005 .050 bsc .030 .005 typ inches (millimeters) note: 1. dimensions in 2. drawing not to scale 3. these dimensions do not include mold flash or protrusions. mold flash or protrusions shall not exceed .006" (0.15mm)
lt6600-15 12 660015fb linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 (408) 432-1900 fax: (408) 434-0507 www.linear.com linear technology corporation 2005 lt 0409 rev b ? printed in usa related parts typical application part number description comments lt c ? 1565-31 650khz linear phase lowpass filter continuous time, so8 package, fully differential ltc1566-1 low noise, 2.3mhz lowpass filter continuous time, so8 package lt1567 very low noise, high frequency filter building block 1.4nv/ hz op amp, msop package, fully differential lt1568 very low noise, 4th order building block lowpass and bandpass filter designs up to 10mhz, differential outputs lt1993-x low distortion, low noise differential ampli? er/adc driver fixed gain of 6db, 12db and 20db lt1994 low distortion, low noise differential ampli? er/adc driver adjustable, low power, v s = 2.375v to 12.6v lt6600-2.5 very low noise differential ampli? er and 2.5mhz lowpass filter 86db s/n with 3v supply, so-8 lt6600-5 very low noise differential ampli? er and 5mhz lowpass filter 82db s/n with 3v supply, so-8 lt6600-10 very low noise differential ampli? er and 10mhz lowpass filter 82db s/n with 3v supply, so-8 lt6600-20 very low noise differential ampli? er and 20mhz lowpass filter 76db s/n with 3v supply, so-8 dual matched i and q lowpass filter and adc (typical phase matching 1 degree) C + r in 536 r in 536 0.1f 0.1f 25 25 lt6600-15 5.6pf 2.2f 3v 0.1f 3v C + 3 4 1 v cma v cmb 7 i 2 8 5 6 C + r in 536 r in 536 0.1f 0.1f 25 25 lt6600-15 5.6pf 660015 ta02 3v C + 3 4 1 7 q 2 8 5 6 gain = 536/r in 2.2f 5.6pf ina inb 5.6pf 5.6pf 5.6pf ltc2299

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