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lt6600-10 1 66001fd typical application features applications description very low noise, differential ampli er and 10mhz lowpass filter the lt ? 6600-10 combines a fully differential ampli? er with a 4th order 10mhz 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 lt6600-10, two external resistors program differential gain, and the ? lters 10mhz cutoff frequency and passband ripple are internally set. the lt6600-10 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 lt6600-10 integrates an antialiasing ? lter and a differential ampli- ? er/driver without compromising distortion or low noise performance. at unity gain the measured in band signal- to-noise ratio is an impressive 82db. 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 lt6600-10 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. for similar devices with other cutoff frequencies, refer to the lt6600-20, lt6600-15, lt6600-5 and lt6600-2.5. an 8192 point fft spectrum 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 10mhz cutoff n 82db s/n with 3v supply and 2v p-p output n low distortion, 2v p-p , 800 load 1mhz: 88dbc 2nd, 97dbc 3rd 5mhz: 74dbc 2nd, 77dbc 3rd n fully differential inputs and outputs n compatible with popular differential ampli? er pinouts n so-8 and dfn-12 packages 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 402 r in 402 0.01f 0.1f 49.9 49.9 18pf 5v 5v C + v mid v ocm v in v cm a in v + v C d out lt6600-10 ltc1748 3 4 1 7 2 8 5 6 6600 ta01a gain = 402/r in 1f frequency (mhz) 0 frequency (db) 4 8 12 16 20 24 28 32 6600 ta01b C10 0 C20 C30 C40 C50 C60 C70 C80 C90 C100 C110 input is a 4.7mhz sinewave 2v p-p f sample = 66mhz (s8 pin numbers shown) l , lt, ltc, ltm, linear technology and the linear logo are registered trademarks of linear technology corporation. all other trademarks are the property of their respective owners.
lt6600-10 2 66001fd 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 (note 1) top view df package 12-lead (4mm s 4mm) plastic dfn 12 13 11 8 9 10 4 5 3 2 1 in + nc v mid v ? v ? out ? in ? nc v ocm v + nc out + 6 7 t jmax = 150c, = = + + + = =
lt6600-10 3 66001fd 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 = 402 , and r load = 1k. electrical characteristics parameter conditions min typ max units filter gain, v s = 3v v in = 2v p-p , f in = dc to 260khz C0.4 0 0.5 db v in = 2v p-p , f in = 1mhz (gain relative to 260khz) l C0.1 0 0.1 db v in = 2v p-p , f in = 5mhz (gain relative to 260khz) l C0.4 C0.1 0.3 db v in = 2v p-p , f in = 8mhz (gain relative to 260khz) l C0.3 0.1 1 db v in = 2v p-p , f in = 10mhz (gain relative to 260khz) l C0.2 0.3 1.7 db v in = 2v p-p , f in = 30mhz (gain relative to 260khz) l C28 C25 db v in = 2v p-p , f in = 50mhz (gain relative to 260khz) l C44 db filter gain, v s = 5v v in = 2v p-p , f in = dc to 260khz C0.5 0 0.5 db v in = 2v p-p , f in = 1mhz (gain relative to 260khz) l C0.1 0 0.1 db v in = 2v p-p , f in = 5mhz (gain relative to 260khz) l C0.4 C0.1 0.3 db v in = 2v p-p , f in = 8mhz (gain relative to 260khz) l C0.4 0.1 0.9 db v in = 2v p-p , f in = 10mhz (gain relative to 260khz) l C0.3 0.2 1.4 db v in = 2v p-p , f in = 30mhz (gain relative to 260khz) l C28 C25 db v in = 2v p-p , f in = 50mhz (gain relative to 260khz) l C44 db filter gain, v s = 5v v in = 2v p-p , f in = dc to 260khz C0.6 C0.1 0.4 db filter gain, r in = 100, v s = 3v, 5v, 5v v in = 0.5v p-p , f in = dc to 260khz 11.4 12 12.6 db filter gain temperature coef? cient (note 2) f in = 260khz, v in = 2v p-p 780 ppm/c noise noise bw = 10khz to 10mhz, r in = 402 56 v rms distortion (note 4) 1mhz, 2v p-p , r l = 800 2nd harmonic 3rd harmonic 88 97 dbc dbc 5mhz, 2v p-p , r l = 800 2nd harmonic 3rd harmonic 74 77 dbc dbc differential output swing measured between pins 4 and 5 v s = 5v pin 7 shorted to pin 2 v s = 3v l l 3.85 3.85 5.0 4.9 v p-p diff v p-p diff input bias current average of pin 1 and pin 8 l C85 C40 a input referred differential offset r in = 402 v s = 3v v s = 5v v s = 5v l l l 5 10 8 20 30 35 mv mv mv r in = 100 v s = 3v v s = 5v v s = 5v l l l 5 5 5 13 22 30 mv mv mv differential offset drift 10 v/c
lt6600-10 4 66001fd 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 = 402 , and r load = 1k. electrical characteristics parameter conditions min typ max units input common mode voltage (note 3) differential input = 500mv p-p , v s = 3v r in = 100 v s = 5v v s = 5v l l l 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 v s = 5v l l l 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 l l l C35 C40 C55 5 0 C5 40 40 35 mv mv mv common mode rejection ratio 61 db voltage at v mid (pin 7) v s = 5 (s8) v s = 5 (dfn) v s = 3 l l 2.46 2.45 2.51 2.51 1.5 2.55 2.56 v v v v mid input resistance l 4.3 5.5 7.7 k v ocm bias current v ocm = v mid = v s /2 v s = 5v v s = 3v l l C15 C10 C3 C3 a a power supply current v s = 3v, v s = 5 v s = 3v, v s = 3 v s = 5v l l 35 36 39 43 46 ma ma ma 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 v ocm , and the voltage at v mid are equal to one half of the total power supply voltage. 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 v ocm . note 6: the lt6600c is guaranteed functional over the operating temperature range C40c to 85c. note 7: the lt6600c 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 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.
lt6600-10 5 66001fd typical performance characteristics amplitude response passband gain and group delay passband gain and group delay output impedance vs frequency (out + or out C ) common mode rejection ratio power supply rejection ratio distortion vs frequency v in = 2v p-p , v s = 3v, r l = 800 at each output, t a = 25c frequency (hz) 100k C30 C20 C10 0 10 1m 10m 100m 6600 g01 C40 C50 C70 C80 C60 gain 20log diffout diffin () v s = 5v gain = 1 frequency (mhz) 0.5 C9 gain (db) group delay (ns) C8 C6 C5 C4 1 C2 14.9 6600 g02 C7 C1 0 C3 10 15 25 30 35 45 20 50 55 60 40 5.3 10.1 v s = 5v gain = 1 t a = 25c frequency (mhz) 0.5 2 gain (db) group delay (ns) 3 5 6 7 12 9 14.9 6600 g03 4 10 11 8 10 15 25 30 35 45 20 50 55 60 40 5.3 10.1 v s = 5v gain = 4 t a = 25c frequency (hz) 100k 0.1 output impedance () 1 10 100 1m 10m 100m 6600 g04 frequency (hz) 100k 60 cmrr (db) 65 70 75 80 1m 10m 100m 6600 g05 55 50 40 35 45 v s = 5v gain = 1 v in = 1v p-p t a = 25c frequency (hz) 20 psrr (db) 30 50 60 80 90 1k 100k 1m 100m 6600 g06 10 10k 10m 70 40 0 v s = 3v v in = 200mv p-p t a = 25 o c v + to diffout frequency (mhz) 0.1 C100 distortion (db) C90 C80 C70 C60 C40 110 6600 g07 C50 differential input, 2nd harmonic differential input, 3rd harmonic single-ended input, 2nd harmonic single-ended input, 3rd harmonic
lt6600-10 6 66001fd typical performance characteristics distortion vs signal level v s = 3v, r l = 800 at each output, t a = 25c distortion vs signal level v s = 5v, r l = 800 at each output, t a = 25c distortion vs input common mode level, 2v p-p , 1mhz input, 1x gain, r l = 800 at each output, t a = 25c distortion vs input common mode level, 0.5v p-p , 1mhz input, 4x gain, r l = 800 at each output, t a = 25c power supply current vs power supply voltage transient response, differential gain = 1 distortion vs output common mode, 2v p-p 1mhz input, 1x gain, t a = 25c input level (v p-p ) 0 C100 distortion (db) C90 C80 C70 C60 C50 C40 1234 6600 g09 5 2nd harmonic, 5mhz input 3rd harmonic, 5mhz input 2nd harmonic, 1mhz input 3rd harmonic, 1mhz input input level (v p-p ) 0 C60 C50 C40 4 6600 g10 C70 C80 123 5 C90 C100 C110 distortion (db) 2nd harmonic, 5mhz input 3rd harmonic, 5mhz input 2nd harmonic, 1mhz input 3rd harmonic, 1mhz input input common mode voltage relative to v mid (v) C3 C100 distortion component (db) C90 C80 C70 C60 C40 C2 C1 0 1 6600 g11 23 C50 2nd harmonic, v s = 3v 3rd harmonic, v s = 3v 2nd harmonic, v s = 5v 3rd harmonic, v s = 5v input common mode voltage relative to v mid (v) C3 C100 distortion component (db) C90 C80 C70 C60 C40 C2 C1 0 1 6600 g12 23 C50 2nd harmonic, v s = 3v 3rd harmonic, v s = 3v 2nd harmonic, v s = 5v 3rd harmonic, v s = 5v total supply voltage (v) 2 power supply current (ma) 32 36 10 6600 g13 28 24 4 6 8 3 5 7 9 40 30 34 26 38 t a = 85c t a = 25c t a = C40c v out + 50mv/div differential input 200mv/div 100ns/div 6600 g14 output common mode voltage (v) C1 C100 distortion component (db) C90 C80 C70 C60 C40 C0.5 0 0.5 1 6600 g15 1.5 2 C50 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 distortion vs frequency v in = 2v p-p , v s = 5v, r l = 800 at each output, t a = 25c frequency (mhz) 0.1 C100 distortion (db) C90 C80 C70 C60 C40 110 6600 g08 C50 differential input, 2nd harmonic differential input, 3rd harmonic single-ended input, 2nd harmonic single-ended input, 3rd harmonic
lt6600-10 7 66001fd pin functions (dfn/s8) in C and in + (pins 1, 12/pins 1, 8): input pins. signals can be applied to either or both input pins through identical external resistors, r in . the dc gain from differential inputs to the differential outputs is 1580/r in . nc (pin 2, 5, 11/na): no connection. v ocm (pin 3/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. this is a high impedance input, which can be driven from an external voltage reference, or can be tied to v mid on the pc board. v ocm should be bypassed with a 0.01f ceramic capacitor unless it is connected to a ground plane. v + and v C (pins 4, 8, 9/pins 3, 6): power supply pins . for a single 3.3v or 5v supply (v C grounded) a quality 0.1f ceramic bypass capacitor is required from the positive supply pin (v + ) to the negative supply pin (v C ). the bypass should be as close as possible to the ic. for dual supply applications, bypass v + to ground and v C to ground with a quality 0.1f ceramic capacitor. out + and out C (pins 6, 7/pins 4, 5): output pins . these are the ? lter differential outputs. each pin can drive a 100 and/or 50pf load to ac ground. v mid (pin 10/pin 7): the v mid pin is internally biased at mid-supply, see block diagram. for single-supply operation the v mid pin should be bypassed with a quality 0.01f ceramic capacitor to v C . for dual supply operation, v mid 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. v mid 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 402 402 200 200 200 200 v + v C 11k 11k op amp proprietary lowpass filter stage v in C v in + r in r in 6600 bd in + v ocm v + out + out C v C v mid in C
lt6600-10 8 66001fd applications information interfacing to the lt6600-10 note: the referenced pin numbers correspond to the s8 package. see the pin functions section for the equivalent dfn-12 package pin numbers. the lt6600-10 requires 2 equal external resistors, r in , to set the differential gain to 402/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 average 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 lt6600-10 are the ? lter outputs. the difference 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 lt6600-10 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 10mhz. the common mode output voltage is determined by the voltage at v ocm . since v ocm is shorted to v mid 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 v mid (refer to the distortion vs input common mode level graphs in the typical performance characteristics section). figure 2 shows how to ac couple signals into the lt6600-10. 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 402 gain setting resistor form a high pass ? lter, attenuating signals below 4khz. larger values of coupling capacitors will proportionally reduce this highpass 3db frequency. in figure 3 the lt6600-10 is providing 12db of gain. the gain resistor has an optional 62pf in parallel to improve the passband ? atness near 10mhz. the common mode output voltage is set to 2v. use figure 4 to determine the interface between the lt6600-10 and a current output dac. the gain, or transimpedance, is de? ned as a = v out /i in . to compute the transimpedance, use the following equation: a = 402 ? r1 r1 + r2 by setting r1 + r2 = 402, the gain equation reduces to a = r1. the voltage at the pins of the dac is determined by r1, r2, the voltage on v mid and the dac output current (i in + or i in C ). consider figure 4 with r1 = 49.9 and r2 = 348. the voltage at v mid is 1.65v. the voltage at the dac pins is given by: v dac = v pin7 ? r1 r1 + r2 + 402 + i in r1? r2 r1 + r2 = 103mv + i in 43.6 i in is i in ? or i in + .the transimpedance in this example is 50.4. evaluating the lt6600-10 the low impedance levels and high frequency operation of the lt6600-10 require some attention to the matching networks between the lt6600-10 and other devices. the previous examples assume an ideal (0) source impedance and a large (1k) load resistance. among practical examples where impedance must be considered is the evaluation of the lt6600-10 with a network analyzer. figure 5 is a laboratory setup that can be used to characterize the lt6600-10 using single-ended instruments with 50 source impedance and 50 input impedance. for a unity gain con? guration the lt6600-10 requires a 402 source resistance yet the network analyzer output is calibrated for a 50 load resistance. the 1:1 transformer, 53.6 and 388 resistors satisfy the two constraints above. the transformer converts the single-ended source into a differential stimulus. similarly, the output the lt6600-10 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
lt6600-10 9 66001fd applications information figure 1. (s8 pin numbers) figure 2. (s8 pin numbers) figure 3. (s8 pin numbers) C + 402 402 0.01f 0.1f 3.3v C + v in C v in + 3 4 1 7 2 8 5 6 6600 f01 v out + v out C v t 3 2 1 v in + v in C v t 3 2 1 v out + lt6600-10 v out C 0 0 C + 402 402 0.01f 0.1f 0.1f 0.1f 3.3v C + v in + 3 4 1 7 2 8 5 6 6600 f02 v out + v out C v 3 2 2 1 v t 1 0 0 C1 v in + lt6600-10 v out + v out C C + 100 100 0.1f 0.01f 0.01f 5v C + v in C v in + 3 4 1 7 2 8 5 6 6600 f03 v out + v out C 62pf 62pf + C 2v v t 3 2 1 0 v in + v in C v t 3 2 1 0 v out + v out C lt6600-10 500mv p-p (diff) figure 4. (s8 pin numbers) C + 0.1f 0.01f 3.3v C + lt6600-10 3 4 v out + i in + i in C v out C 1 7 2 8 5 6 6600 f04 current output dac r1 r1 r2 r2
lt6600-10 10 66001fd applications information figure 5, present the output of the lt6600-10 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 between the transformer and analyzer input. voltage of v mid . 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 v mid . figure 5. (s8 pin numbers) C + 0.1f 0.1f 2.5v C2.5v C + lt6600-10 3 4 1 7 2 8 5 6 6600 f05 402 402 network analyzer input 50 coilcraft ttwb-16a 4:1 network analyzer source coilcraft ttwb-1010 1:1 50 53.6 388 388 figure 6 1mhz input level (v p-p ) 0 20 0 C20 C40 C60 C80 C100 C120 35 6600 f06 12 46 output level (dbv) 3rd harmonic 85c 1db passband gain compression points 1mhz 25c 1mhz 85c 3rd harmonic 25c 2nd harmonic 25c 2nd harmonic 85c differential and common mode voltage ranges the differential ampli? ers inside the lt6600-10 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 ltc6600-10 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 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 lt6600-10 have independent control of their output common mode voltage (see the block diagram section). the following guidelines will optimize the performance of the ? lter for single-supply operation. v mid must be bypassed to an ac ground with a 0.01f or higher capacitor. v mid 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 v ocm can be shorted to v mid for simplicity. if a different common mode output voltage is required, connect v ocm to a voltage source or resistor network. for 3v and 3.3v supplies the voltage at v ocm must be less than or equal to the mid-supply level. for example, voltage (v ocm ) 1.65v on a single 3.3v supply. for power supply voltages higher than 3.3v the voltage at v ocm can be set above mid-supply. the voltage on v ocm should not be more than 1v below the voltage on v mid . the voltage on v ocm should not be more than 2v above the voltage on v mid . v ocm is a high impedance input. the lt6600-10 was designed to process a variety of input signals including signals centered around the mid-supply 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 the electrical characteristics section). common mode dc currents in applications like figure 1 and figure 3 where the lt6600-10 not only provides lowpass ? ltering but also level shifts the common mode voltage of the input signal, dc
lt6600-10 11 66001fd applications information 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. v mid sets the output common mode voltage of the 1st differential ampli? er inside the lt6600-10 (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 402 feedback resistor and the external 100 input resistor. the resulting 5ma common mode dc current in each input path, must be absorbed by the sources v in + and v in C . v ocm sets the common mode output voltage of the 2nd differential ampli? er inside the lt6600-10, and therefore sets the common mode output voltage of the ? lter. since in the example, figure 3, v ocm differs from v mid 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 12.5ma is used to translate the common mode voltages. a simple modi? cation to figure 3 will reduce the dc common mode currents by 36%. if v mid is shorted to v ocm the common mode output voltage of both op amp stages will be 2v and the resulting dc current will be 8ma. of course, by ac coupling the inputs of figure 3, the common mode dc current can be reduced to 2.5ma. noise the noise performance of the lt6600-10 can be evaluated with the circuit of figure 7. given the low noise output of the lt6600-10 and the 6db attenuation of the transformer coupling network, it will be 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, measure the total integrated noise (e s ) of the spectrum analyzer from 10khz to 10mhz. 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 function of frequency for an lt6600-10 with r in = 402 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 10mhz input referred noise dbm/hz 4 100 24v rms C149 2 200 34v rms C146 1 402 56v rms C142 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. figure 7. (s8 pin numbers) C + 0.1f 0.1f 2.5v C2.5v C + lt6600-10 3 4 1 7 2 8 5 6 r in r in 25 25 6600 f07 spectrum analyzer input 50 v in coilcraft ttwb-1010 1:1
lt6600-10 12 66001fd applications information power dissipation the lt6600-10 ampli? ers combine high speed with large-signal currents in a small package. there is a need to ensure that the diess junction temperature does not exceed 150c. the lt6600-10 s8 package has pin 6 fused to the lead frame to enhance thermal conduction when connecting 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 lt6600-10 s8 (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. table 2. lt6600-10 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 dissipation occurs when the differential input signal is maximum, 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 junction 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 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 v + ) measures 48.9ma. assuming 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 ? 0.0489 ? 100) = 109c when using higher supply voltages or when driving small impedances, more copper may be necessary to keep t j below 150c. figure 8 frequency (mhz) 0.1 spectral density (nv rms /hz) integrated noise (mv rms ) 35 30 25 20 15 10 5 0 140 120 100 80 60 40 20 0 1.0 10 100 6600 f08 spectral density integrated noise
lt6600-10 13 66001fd package description df package 12-lead plastic dfn (4mm 4mm) (reference ltc dwg # 05-08-1733 rev ?) 4.00 0.10 (4 sides) note: 1. drawing is proposed to be made a jedec package outline mo-220 variation (wggd-x)?to be approved 2. drawing not to scale 3. all dimensions are in millimeters 4. dimensions of exposed pad on bottom of package do not include mold flash. mold flash, if present, shall not exceed 0.15mm on any side 5. exposed pad shall be solder plated 6. shaded area is only a reference for pin 1 location on the top and bottom of package pin 1 top mark (note 6) 0.40 0.10 1 6 12 7 bottom view?exposed pad 2.65 0.10 0.75 0.05 r = 0.115 typ 0.25 0.05 0.50 bsc 2.50 ref 3.3 8 0.10 0.200 ref 0.00 ? 0.05 (df12) dfn 0 8 06 rev ? recommended solder pad pitch and dimensions apply solder mask to areas that are not soldered 0.70 0.05 0.25 0.05 0.50 bsc 3.10 0.05 4.50 0.05 package outline pin 1 notch r = 0.20 typ or 0.35 45 chamfer 2.65 0.05 3.3 8 0.05 2.50 ref
lt6600-10 14 66001fd package description s8 package 8-lead plastic small outline (narrow .150 inch) (reference ltc dwg # 05-08-1610) .016 ? .050 (0.406 ? 1.270) .010 ? .020 (0.254 ? 0.50 8 ) 45 0 ? 8 typ .00 8 ? .010 (0.203 ? 0.254) so 8 0303 .053 ? .069 (1.346 ? 1.752) .014 ? .019 (0.355 ? 0.4 8 3) typ .004 ? .010 (0.101 ? 0.254) .050 (1.270) bsc 1 2 3 4 .150 ? .157 (3. 8 10 ? 3.9 88 ) note 3 8 7 6 5 .1 8 9 ? .197 (4. 8 01 ? 5.004) note 3 .22 8 ? .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)
lt6600-10 15 66001fd 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. revision history rev date description page number d 5/10 updated order information section 2 (revision history begins at rev d)
lt6600-10 16 66001fd linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 (408) 432-1900 fax: (408) 434-0507 www.linear.com linear technology corporation 2002 lt 0510 rev d ? printed in usa related parts typical applications 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, fully differential lt1567 very low noise, high frequency filter building block 1.4nv/ hz op amp, msop package, differential output lt1568 very low noise, 4th order building block lowpass and bandpass filter designs up to 10mhz, differential outputs ltc6600-2.5 very low noise, differential ampli? er and 2.5mhz lowpass filter adjustable output common mode voltage ltc6600-20 very low noise, differential ampli? er and 20mhz lowpass filter adjustable output common mode voltage 5th order, 10mhz lowpass filter (s8 pin numbers shown) amplitude response transient response 5th order, 10mhz lowpass filter differential gain = 1 amplitude response amplitude respo a wcdma transmit filter (10mhz lowpass filter with a 28mhz notch, s8 pin numbers shown) C + r c r r r 0.1f 0.1f v + v C C + 3 4 1 7 2 8 5 6 v out + v out C lt6600-10 v out + v out C 6600 ta02a v in C v in + c = 1 2 p ? r ? 10mhz gain = , maximum gain = 4 402 2r frequency (hz) 100k C30 gain (db) C20 C10 0 10 1m 10m 100m 6600 ta02b C40 C50 C70 C80 C60 differential gain = 1 r = 200 c = 82pf v out + 50mv/div differential input 200mv/div 100ns/div 6600 ta02c C + 100 27pf r q 301 100 1h 33pf 33pf 0.1f 0.1f v + v C C + 3 4 1 7 2 8 5 6 v out + v out C lt6600-10 v out + v out C 6600 ta03a v in C v in + gain = 12db inductors are coilcraft 1008ps-102m 1h frequency (hz) 200k C18 gain (db) C8 2 12 22 1m 10m 100m 6600 ta03b C28 C38 C58 C68 C78 C48

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