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LT6600-5 1 66005fa typical application description very low noise, differential ampli er and 5mhz lowpass filter the lt ? 6600-5 combines a fully differential ampli? er with a 4th order 5mhz 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 LT6600-5, two external resistors program differential gain, and the ? lters 5mhz cutoff frequency and passband ripple are internally set. the LT6600-5 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 LT6600-5 integrates an antialiasing ? lter and a differential ampli- ? er/driver without compromising distortion or low noise performance. at unity gain the measured in band sig- nal-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 LT6600-5 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, lt6600-10 and lt6600-2.5. dual, matched, 5mhz lowpass filter 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 5mhz cutoff n 82db s/n with 3v supply and 2v p-p output n low distortion, 2v p-p , 800 load 1mhz: 93dbc 2nd, 96dbc 3rd n fully differential inputs and outputs n compatible with popular differential ampli? er pinouts n available in an 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 5mhz phase distribution (50 units) C C + + C C + + 3v 3v r in v ocm (1v-1.5v) i in q in q out i out r in r in r in 0.1f 0.01f 0.01f 0.1f gain = 806 r in 5mhz phase (deg) percentage of units (%) 66005 ta01 30 25 20 15 10 5 0 C135 C134 C133 C132.5 C134.5 C133.5 C132 C131.5 LT6600-5 LT6600-5 3 4 5 6 7 1 2 8 3 4 5 6 7 1 2 8
LT6600-5 2 66005fa pin configuration absolute maximum ratings total supply voltage .................................................11v input voltage (note 8) ............................................... v s input current (note 8) ..........................................10ma operating temperature range (note 6).... C40c to 85c speci? ed temperature range (note 7) .... C40c to 85c junction temperature ........................................... 150c storage temperature range ...................C 65c to 150c lead temperature (soldering, 10 sec) .................. 300c (note 1) top view in + v mid v C out C in C v ocm v + out + s8 package 8-lead plastic so 1 2 3 4 8 7 6 5 t jmax = 150c, ja = 100c/w parameter conditions min typ max units filter gain, v s = 3v v in = 2v p-p , f in = dc to 260khz C 0.5 0 0.5 db v in = 2v p-p , f in = 500k (gain relative to 260khz) l C0.15 0 0.1 db v in = 2v p-p , f in = 2.5mhz (gain relative to 260khz) l C0.4 C 0.1 0.3 db v in = 2v p-p , f in = 4mhz (gain relative to 260khz) l C0.7 C0.1 0.6 db v in = 2v p-p , f in = 5mhz (gain relative to 260khz) l C1.1 C0.2 0.8 db v in = 2v p-p , f in = 15mhz (gain relative to 260khz) l C 28 C25 db v in = 2v p-p , f in = 25mhz (gain relative to 260khz) l C44 db filter gain, v s = 5v v in = 2v p-p , f in = dc to 260khz C 0.5 0 0.5 db v in = 2v p-p , f in = 500k (gain relative to 260khz) l C 0.15 0 0.1 db v in = 2v p-p , f in = 2.5mhz (gain relative to 260khz) l C0.4 C 0.1 0.3 db v in = 2v p-p , f in = 4mhz (gain relative to 260khz) l C 0.7 C0.1 0.6 db v in = 2v p-p , f in = 5mhz (gain relative to 260khz) l C 1.1 C0.2 0.8 db v in = 2v p-p , f in = 15mhz (gain relative to 260khz) l C 28 C25 db v in = 2v p-p , f in = 25mhz (gain relative to 260khz) l C44 db filter gain, v s = 5v v in = 2v p-p , f in = dc to 260khz C 0.6 C0.1 0.4 db order information lead free finish tape and reel part marking package description specified temperature range lt6600cs8-5#pbf lt6600cs8-5#trpbf 66005 8-lead plastic so C40c to 85c lt6600is8-5#pbf lt6600is8-5#trpbf 6600i5 8-lead plastic so C40c to 85c lead based finish tape and reel part marking package description specified temperature range lt6600cs8-5 lt6600cs8-5#tr 66005 8-lead plastic so C40c to 85c lt6600is8-5 lt6600is8-5#tr 6600i5 8-lead plastic so C40c to 85c consult ltc marketing for parts speci? ed with wider operating temperature ranges. for more information on lead free part marking, go to: http://www.linear.com/leadfree/ for more information on tape and reel speci? cations, go to: http://www.linear.com/tapeandreel/ electrical characteristics 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 = 806 , and r load = 1k.
LT6600-5 3 66005fa 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 229. 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 = 806 , and r load = 1k. parameter conditions min typ max units filter gain, r in = 229 v in = 2v p-p , f in = dc to 260khz v s = 3v v s = 5v v s = 5v 10.4 10.3 10.1 10.9 10.8 10.7 11.5 11.4 11.3 db db db filter gain temperature coef? cient (note 2) f in = 260khz, v in = 2v p-p 780 ppm/c noise noise bw = 10khz to 5mhz, r in = 806 45 v rms distortion (note 4) 1mhz, 2v p-p , r l = 800 2nd harmonic 3rd harmonic 93 96 dbc dbc 5mhz, 2v p-p , r l = 800 2nd harmonic 3rd harmonic 66 73 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 4.8 4.8 v p-p diff v p-p diff input bias current average of pin 1 and pin 8 l C70 C30 a input referred differential offset r in = 806 v s = 3v v s = 5v v s = 5v l l l 5 10 8 25 30 35 mv mv mv r in = 229 v s = 3v v s = 5v v s = 5v l l l 5 5 5 13 16 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 = 229 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 output = 2v p-p , v s = 3v pin 7 at midsupply v s = 5v v s = 5v l l l 1.0 1.5 C2.5 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 C25 C30 C55 5 0 C5 50 45 35 mv mv mv common mode rejection ratio 61 db voltage at v mid (pin 7) v s = 5 v s = 3 l 2.46 2.51 1.5 2.55 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 = 5 v s = 3 l l C15 C10 C3 C3 a a power supply current v s = 3v, v s = 5 v s = 3v, v s = 5 v s = 5v l l 28 30 31 34 38 ma ma ma 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 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.
LT6600-5 4 66005fa typical performance characteristics output impedance vs frequency common mode rejection ratio power supply rejection ratio distortion vs frequency distortion vs frequency distortion vs signal level amplitude response passband gain and delay passband gain and delay frequency (mhz) 0.1 C30 C20 C10 0 10 1 10 100 66005 g01 C40 C50 C70 C80 C60 gain (db) v s = 5v gain = 1 t a = 25c frequency (mhz) 0 C9 gain (db) delay (ns) C8 C6 C5 C4 1 C2 7 66005 g02 C7 C1 0 C3 20 30 50 60 70 90 40 100 110 120 80 2 4 1 3 56 8910 gain = 1 t a = 25c delay gain 66005 g03 20 30 50 60 70 90 40 100 110 120 80 frequency (mhz) 07 2 4 1 3 56 8910 gain (db) delay (ns) 3 5 6 7 12 13 9 4 10 11 8 gain = 4 t a = 25c delay gain 66005 g04 frequency (mhz) 0.1 0.1 output impedance () 1 10 100 1 10 100 v s = 5v gain = 1 t a = 25c 66005 g05 frequency (mhz) cmrr (db) 90 80 70 60 50 40 30 0.01 1 10 100 0.1 v s = 5v gain = 1 v in = 1v p-p t a = 25c 66005 g06 frequency (mhz) 0.01 1 10 100 0.1 psrr (db) 80 70 60 50 40 30 20 10 0 v s = 3v v in = 200mv p-p t a = 25c v + to diffout 66005 g07 frequency (mhz) 0.1 C100 distortion (db) C90 C80 C70 C60 C110 110 C50 differential input, 2nd harmonic differential input, 3rd harmonic single-ended input, 2nd harmonic single-ended input, 3rd harmonic v s = 3v, v in = 2v p-p r l = 800, t a = 25c 66005 g08 frequency (mhz) 0.1 C100 distortion (db) C90 C80 C70 C60 C110 110 C50 differential input, 2nd harmonic differential input, 3rd harmonic single-ended input, 2nd harmonic single-ended input, 3rd harmonic v s = 5v, v in = 2v p-p r l = 800, t a = 25c 66005 g09 C60 C50 C40 C70 C80 C90 C100 C110 input level (v p-p ) 0 distortion (db) 12345 2nd harmonic, 5mhz input 3rd harmonic, 5mhz input 2nd harmonic, 1mhz input 3rd harmonic, 1mhz input v s = 3v r l = 800 t a = 25c
LT6600-5 5 66005fa typical performance characteristics power supply current vs power supply voltage transient response, differential gain = 1, single-ended input, differential output distortion vs temperature distortion vs output common mode input referred noise distortion vs signal level distortion vs input common mode distortion vs input common mode 66005 g10 input level (v p-p ) 0 C60 C50 C40 4 C70 C80 123 5 C90 C100 C110 distortion (db) 3rd harmonic 5mhz input 3rd harmonic 1mhz input 2nd harmonic 5mhz input 2nd harmonic 1mhz input v s = 5v r l = 800, t a = 25c 66005 g11 input common mode voltage relative to pin 7 (v) C3 C110 C100 distortion component (db) C90 C80 C70 C60 C40 C2 C1 0 1 23 C50 2nd harmonic, v s = 3v 3rd harmonic, v s = 3v 2nd harmonic, v s = 5v 3rd harmonic, v s = 5v gain = 1, pin 7 = v s /2 2v p-p 1mhz input r l = 800, t a = 25c 66005 g12 input common mode voltage relative to pin 7 (v) C3 C110 C100 distortion component (db) C90 C80 C70 C60 C40 C2 C1 0 1 23 C50 2nd harmonic, v s = 3v 3rd harmonic, v s = 3v 2nd harmonic, v s = 5v 3rd harmonic, v s = 5v gain = 4, pin 7 = v s /2 2v p-p 1mhz input r l = 800, t a = 25c 66005 g13 total supply voltage (v) 2 power supply current (ma) 32 36 12 10 28 24 4 6 8 20 30 34 26 22 t a = 85c t a = 25c t a = C40c 66005 g14 out C 200mv/div out + 200mv/div in C 500mv/div in + 100ns/div 66005 g15 1mhz input level (v p-p ) 0 20 0 C20 C40 C60 C80 C100 C120 35 12 467 output level (dbv) 1db passband gain compression points 1mhz t a = 25c 1mhz t a = 85c 3rd harmonic t a = 85c 3rd harmonic t a = 25c 2nd harmonic t a = 25c 2nd harmonic t a = 85c 66005 g16 voltage pin 2 to pin 7 (v) C1.5 C1.0 C100 distortion component (db) C90 C80 C70 C60 C40 C0.5 0 0.5 1.0 1.5 2.5 2.0 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 gain = 4 pin 7 = v s /2 t a = 25c 0.5v p-p 1mhz input r l = 800 C110 66005 g17 frequency (mhz) 0.01 noise density (nv/ hz ) integrated noise (v) 100 45 40 35 30 25 20 15 10 5 0 90 80 70 60 50 40 30 20 10 0 0.1 10 integrated noise, gain = 1x integrated noise, gain = 4x noise density, gain = 1x noise density, gain = 4x
LT6600-5 6 66005fa 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 806/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 to ac ground. v mid (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 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 806 806 400 400 400 400 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 66005 bd in + v ocm v + out + out C v C v mid in C
LT6600-5 7 66005fa applications information interfacing to the LT6600-5 the LT6600-5 requires 2 equal external resistors, r in , to set the differential gain to 806/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 LT6600-5 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 LT6600-5 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 5mhz. 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 (refer to the distortion vs input common mode level graphs in the typical performance characteristics). figure 2 shows how to ac couple signals into the LT6600-5. in this instance, the input is a single-ended signal. ac coupling allows the processing of single-ended or dif- ferential signals with arbitrary common mode levels. the 0.1f coupling capacitor and the 806 gain setting resistor form a high pass ? lter, attenuating signals below 2khz. larger values of coupling capacitors will proportionally reduce this highpass 3db frequency. in figure 3 the LT6600-5 is providing 12db of gain. the gain resistor has an optional 62pf in parallel to improve figure 1 figure 2 figure 3 C + 806 806 0.01f 0.1f 3.3v C + v in C v in + 3 4 1 7 2 8 5 6 66005 f01 v out + v out C v t 3 2 1 v in + v in C v t 3 2 1 v out + LT6600-5 v out C 0 0 C + 806 806 0.01f 0.1f 0.1f 0.1f 3.3v C + v in + 3 4 1 7 2 8 5 6 66005 f02 v out + v out C v 3 2 2 1 v t 1 0 0 C1 v in + LT6600-5 v out + v out C C + 200 200 0.1f 0.01f 0.01f 5v C + v in C v in + 3 4 1 7 2 8 5 6 66005 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 LT6600-5 500mv p-p (diff)
LT6600-5 8 66005fa applications information the passband ? atness near 5mhz. the common mode output voltage is set to 2v. use figure 4 to determine the interface between the LT6600-5 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 = 806 ? r1 r1 + r2 v dac = v pin7 ? r1 r1 + r2 + 806 + i in r1? r2 r1 + r2 = 51mv + i in 46.8 figure 4 C + 0.1f 0.01f 3.3v C + LT6600-5 3 4 v out + i in + i in C v out C 1 7 2 8 5 6 66005 f04 current output dac r1 r1 r2 r2 evaluating the LT6600-5 the low impedance levels and high frequency operation of the LT6600-5 require some attention to the matching networks between the LT6600-5 and other devices. the previous examples assume an ideal (0) source imped- ance and a large (1k) load resistance. among practi- cal examples where impedance must be considered is the evaluation of the LT6600-5 with a network analyzer. figure 5 is a laboratory setup that can be used to character- ize the LT6600-5 using single-ended instruments with 50 source impedance and 50 input impedance. for a unity gain con? guration the LT6600-5 requires a 806 source resistance yet the network analyzer output is calibrated for a 50 load resistance. the 1:1 transformer, 51.1 and 787 resistors satisfy the two constraints above. the transformer converts the single-ended source into a differential stimulus. similarly, the output the LT6600-5 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 LT6600-5 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 LT6600-5 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 ltc6600-5 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. figure 5 C + 0.1f 0.1f 2.5v C2.5v C + LT6600-5 3 4 1 7 2 8 5 6 66005 f05 402 402 network analyzer input 50 coilcraft ttwb-16a 4:1 network analyzer source coilcraft ttwb-1010 1:1 50 51.1 787 787
LT6600-5 9 66005fa applications information the two ampli? ers inside the LT6600-5 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. pin 7 must be bypassed to an ac ground with a 0.01f or higher 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 can be set above mid-supply. the voltage on pin 2 should not be more than 1v below the voltage on pin 7. the voltage on pin 2 should not be more than 2v above the voltage on pin 7. pin 2 is a high impedance input. the LT6600-5 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 electrical characteristics). common mode dc currents in applications like figure 1 and figure 3 where the LT6600-5 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 LT6600-5 (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 806 feedback resistor and the external 200 input resistor. the resulting 2.5ma 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 LT6600-5, and therefore sets the common mode output voltage of the ? lter. since in the example, figure 3, pin 2 differs from pin 7 by 0.5v, an additional 1.25ma (0.625ma 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 6.25ma is used to translate the common mode voltages. a simple modi? cation to figure 3 will reduce the dc com- mon mode currents by 36%. 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 4ma. of course, by ac coupling the inputs of figure 3 and shorting pin 7 to pin 2, the common mode dc current is eliminated. noise the noise performance of the LT6600-5 can be evaluated with the circuit of figure 7. given the low noise output of the LT6600-5 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. figure 6 1mhz input level (v p-p ) 0 20 0 C20 C40 C60 C80 C100 C120 35 66005 f06 12 467 output level (dbv) 1db passband gain compression points 1mhz t a = 25c 1mhz t a = 85c 3rd harmonic t a = 85c 3rd harmonic t a = 25c 2nd harmonic t a = 25c 2nd harmonic t a = 85c
LT6600-5 10 66005fa applications information example: with the ic removed and the 25 resistors grounded, measure the total integrated noise (e s ) of the spectrum analyzer from 10khz to 5mhz. with the ic in- serted, 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 LT6600-5 with r in = 806 and 200 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 4 200 24v rms C149 2 402 38v rms C145 1 806 69v rms C140 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 LT6600-5 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 LT6600-5 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 cop- per, a total of 660 square millimeters connected to pin 6 of the LT6600-5 (330 square millimeters on each side of the pc board) will result in a thermal resistance, ja , of about 85c/w. without 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. LT6600-5 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 figure 7 figure 8 C + 0.1f 0.1f 2.5v C2.5v C + LT6600-5 3 4 1 7 2 8 5 6 r in r in 25 25 66005 f07 spectrum analyzer input 50 v in coilcraft ttwb-1010 1:1 frequency (mhz) 0.01 noise density (nv/ hz ) integrated noise (v) 100 45 40 35 30 25 20 15 10 5 0 90 80 70 60 50 40 30 20 10 0 66005 g08 0.1 10 integrated noise, gain = 1x integrated noise, gain = 4x noise density, gain = 1x noise density, gain = 4x
LT6600-5 11 66005fa 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. applications information s8 package 8-lead plastic small outline (narrow .150 inch) (reference ltc dwg # 05-08-1610) 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 volt- ages. for a given supply voltage, the worst-case power dis- sipation occurs when the differential input signal is maximum, the common mode currents are maximum (see applications information regarding common mode dc currents), the load impedance is small and the ambi- ent 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 volt- age of 250mv, a differential output voltage of 1v, 1k load resistance and an ambient temperature of 85c, the supply current (current into pin 3) measures 32.2ma. 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 ? 0.0322 ? 100) = 101c 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)
LT6600-5 12 66005fa linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 (408) 432-1900 fax: (408) 434-0507 www.linear.com ? linear technology corporation 2004 lt 0408 rev a ? 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, 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 ltc1569-7 linear phase, dc accurate, tunable 10th order lowpass filter one external resistor sets filter cutoff frequency, differential inputs lt6600-2.5 very low noise, differential ampli? er and 2.5mhz lowpass filter adjustable output common mode voltage lt6600-10 very low noise, differential ampli? er and 10mhz lowpass filter adjustable output common mode output voltage lt6600-20 very low noise, differential ampli? er and 20mhz lowpass filter adjustable output common mode voltage dual, matched, 6th order, 5mhz lowpass filter single-ended input (i in and q in ) and differential output (i out and q out ) amplitude response C C + + C C + + v + v C v C v + v C v + 806 i in q in q out i out 806 806 806 0.1f 0.1f 0.1f 0.1f 0.1f 0.1f v + inva sa outa outa gnda nc v C v + invb sb outb outb gndb en v C 1 2 3 4 5 6 7 8 16 15 14 13 12 11 10 9 lt1568 LT6600-5 LT6600-5 249 249 249 249 249 249 66005 ta02 gain = or = 1 i out i in q out q in 3 4 5 6 7 1 2 8 3 4 5 6 7 1 2 8 transient response frequency (hz) 100 gain (db) 20 log (i out /i in ) or 20 log (q out /q in ) 12 0 C12 C24 C36 C48 C60 C72 C84 C96 C108 11040 66005 ta02b 66005 ta02c output (i out or q out ) 200mv/div input (i in or q in ) 500mv/div 100ns/div

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