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LM6171 high speed low power low distortion voltage feedback amplifier general description the LM6171 is a high speed unity-gain stable voltage feed- back amplifier. it offers a high slew rate of 3600v/s and a unity-gain bandwidth of 100 mhz while consuming only 2.5 ma of supply current. the LM6171 has very impressive ac and dc performance which is a great benefit for high speed signal processing and video applications. the 15v power supplies allow for large signal swings and give greater dynamic range and signal-to-noise ratio. the LM6171 has high output current drive, low sfdr and thd, ideal for adc/dac systems. the LM6171 is specified for 5v operation for portable applications. the LM6171 is built on national's advanced vip ? iii (verti- cally integrated pnp) complementary bipolar process. features (typical unless otherwise noted) n easy-to-use voltage feedback topology n very high slew rate: 3600v/s n wide unity-gain-bandwidth product: 100 mhz n ?3 db frequency @ a v = +2: 62 mhz n low supply current: 2.5 ma n high cmrr: 110 db n high open loop gain: 90 db n specified for 15v and 5v operation applications n multimedia broadcast systems n line drivers, switchers n video amplifiers n ntsc, pal ? and secam systems n adc/dac buffers n hdtv amplifiers n pulse amplifiers and peak detectors n instrumentation amplifier n active filters typical performance characteristics vip ? is a trademark of national semiconductor corporation. pal ? is a registered trademark of and used under licence from advanced micro devices, inc. closed loop frequency response vs supply voltage (a v = +1) ds012336-5 large signal pulse response a v = +1, v s = 15 ds012336-9 may 1998 LM6171 high speed low power low distortion voltage feedback amplifier ? 1999 national semiconductor corporation ds012336 www.national.com
connection diagram ordering information package temperature range transport media nsc drawing industrial ?40c to +85c 8-pin LM6171ain rails n08e molded dip LM6171bin 8-pin LM6171aim, LM6171bim rails m08a small outline LM6171aimx, LM6171bimx tape and reel 8-pin dip/so ds012336-1 top view www.national.com 2
absolute maximum ratings (note 1) if military/aerospace specified devices are required, please contact the national semiconductor sales office/ distributors for availability and specifications. esd tolerance (note 2) 2.5 kv supply voltage (v + v ? ) 36v differential input voltage (note 11) 10v common-mode voltage range v + ?1.4v to v ? + 1.4v output short circuit to ground (note 3) continuous storage temperature range ?65c to +150c maximum junction temperature (note 4) 150c operating ratings (note 1) supply voltage 2.75v v + 18v junction temperature range LM6171ai, LM6171bi ?40c t j +85c thermal resistance ( q ja ) n package, 8-pin molded dip 108c/w m package, 8-pin surface mount 172c/w 15v dc electrical characteristics unless otherwise specified, all limits guaranteed for t j = 25c, v + = +15v, v ? = ?15v, v cm = 0v, and r l = 1k w . boldface limits apply at the temperature extremes typ LM6171ai LM6171bi symbol parameter conditions (note 5) limit limit units (note 6) (note 6) v os input offset voltage 1.5 3 6 mv 58 max tc v os input offset voltage average drift 6 v/c i b input bias current 1 3 3 a 44 max i os input offset current 0.03 2 2 a 33 max r in input resistance common mode 40 m w differential mode 4.9 r o open loop 14 w output resistance cmrr common mode v cm = 10v 110 80 75 db rejection ratio 75 70 min psrr power supply v s = 15v to 5v 95 85 80 db rejection ratio 80 75 min v cm input common-mode cmrr 3 60 db 13.5 v voltage range a v large signal voltage r l = 1k w 90 80 80 db gain (note 7) 70 70 min r l = 100 w 83 70 70 db 60 60 min v o output swing r l = 1k w 13.3 12.5 12.5 v 12 12 min ?13.3 ?12.5 ?12.5 v ?12 ?12 max r l = 100 w 11.6 9 9 v 8.5 8.5 min ?10.5 ?9 ?9 v ?8.5 ?8.5 max continuous output current sourcing, r l = 100 w 116 90 90 ma (open loop) (note 8) 85 85 min sinking, r l = 100 w 105 90 90 ma 85 85 max www.national.com 3
15v dc electrical characteristics (continued) unless otherwise specified, all limits guaranteed for t j = 25c, v + = +15v, v ? = ?15v, v cm = 0v, and r l = 1k w . boldface limits apply at the temperature extremes typ LM6171ai LM6171bi symbol parameter conditions (note 5) limit limit units (note 6) (note 6) continuous output current sourcing, r l = 10 w 100 ma (in linear region) sinking, r l = 10 w 80 ma i sc output short sourcing 135 ma circuit current sinking 135 ma i s supply current 2.5 4 4 ma 4.5 4.5 max 15v ac electrical characteristics unless otherwise specified, all limits guaranteed for t j = 25c, v + = +15v, v ? = ?15v, v cm = 0v, and r l = 1k w . boldface limits apply at the temperature extremes typ LM6171ai LM6171bi symbol parameter conditions (note 5) limit limit units (note 6) (note 6) sr slew rate (note 9) a v = +2, v in = 13 v pp 3600 v/s a v = +2, v in = 10 v pp 3000 gbw unity gain-bandwidth product 100 mhz ?3 db frequency a v = +1 160 mhz a v = +2 62 mhz f m phase margin 40 deg t s settling time (0.1 % )a v = ?1, v out = 5v 48 ns r l = 500 w propagation delay v in = 5v, r l = 500 w ,6 ns a v = ?2 a d differential gain (note 10) 0.03 % f d differential phase (note 10) 0.5 deg e n input-referred f = 1 khz 12 voltage noise i n input-referred f = 1 khz 1 current noise 5v dc electrical characteristics unless otherwise specified, all limits guaranteed for t j = 25c, v + = +5v, v ? = ?5v, v cm = 0v, and r l = 1k w . boldface limits apply at the temperature extremes typ LM6171ai LM6171bi symbol parameter conditions (note 5) limit limit units (note 6) (note 6) v os input offset voltage 1.2 3 6 mv 58 max tc v os input offset voltage 4 v/c average drift i b input bias current 1 2.5 2.5 a 3.5 3.5 max i os input offset current 0.03 1.5 1.5 a 2.2 2.2 max www.national.com 4
5v dc electrical characteristics (continued) unless otherwise specified, all limits guaranteed for t j = 25c, v + = +5v, v ? = ?5v, v cm = 0v, and r l = 1k w . boldface limits apply at the temperature extremes typ LM6171ai LM6171bi symbol parameter conditions (note 5) limit limit units (note 6) (note 6) r in input resistance common mode 40 m w differential mode 4.9 r o open loop 14 w output resistance cmrr common mode v cm = 2.5v 105 80 75 db rejection ratio 75 70 min psrr power supply v s = 15v to 5v 95 85 80 db rejection ratio 80 75 min v cm input common-mode cmrr 3 60 db 3.7 v voltage range a v large signal voltage r l = 1k w 84 75 75 db gain (note 7) 65 65 min r l = 100 w 80 70 70 db 60 60 min v o output swing r l = 1k w 3.5 3.2 3.2 v 33 min ?3.4 ?3.2 ?3.2 v ?3 ?3 max r l = 100 w 3.2 2.8 2.8 v 2.5 2.5 min ?3.0 ?2.8 ?2.8 v ?2.5 ?2.5 max continuous output current sourcing, r l = 100 w 32 28 28 ma (open loop) (note 8) 25 25 min sinking, r l = 100 w 30 28 28 ma 25 25 max i sc output short sourcing 130 ma circuit current sinking 100 ma i s supply current 2.3 3 3 ma 3.5 3.5 max 5v ac electrical characteristics unless otherwise specified, all limits guaranteed for t j = 25c, v + = +5v, v ? = ?5v, v cm = 0v, and r l = 1k w . boldface limits apply at the temperature extremes typ LM6171ai LM6171bi symbol parameter conditions (note 5) limit limit units (note 6) (note 6) sr slew rate (note 9) a v = +2, v in = 3.5 v pp 750 v/s gbw unity gain-bandwidth 70 mhz product ?3 db frequency a v = +1 130 mhz a v = +2 45 f m phase margin 57 deg t s settling time (0.1 % )a v = ?1, v out = +1v, 60 ns r l = 500 w propagation delay v in = 1v, r l = 500 w ,8 ns www.national.com 5
5v ac electrical characteristics (continued) unless otherwise specified, all limits guaranteed for t j = 25c, v + = +5v, v ? = ?5v, v cm = 0v, and r l = 1k w . boldface limits apply at the temperature extremes typ LM6171ai LM6171bi symbol parameter conditions (note 5) limit limit units (note 6) (note 6) a v = ?2 a d differential gain (note 10) 0.04 % f d differential phase (note 10) 0.7 deg e n input-referred f = 1 khz 11 voltage noise i n input-referred f = 1 khz 1 current noise note 1: absolute maximum ratings indicate limits beyond which damage to the device may occur. operating ratings indicate conditions for which the device is i n- tended to be functional, but specific performance is not guaranteed. for guaranteed specifications and the test conditions, see the electrical char acteristics. note 2: human body model, 1.5 k w in series with 100 pf. note 3: continuous short circuit operation at elevated ambient temperature can result in exceeding the maximum allowed junction temperature of 150c. note 4: the maximum power dissipation is a function of t j(max) , q ja , and t a . the maximum allowable power dissipation at any ambient temperature is p d = (t j(max) ?t a )/ q ja . all numbers apply for packages soldered directly into a pc board. note 5: typical values represent the most likely parametric norm. note 6: all limits are guaranteed by testing or statistical analysis. note 7: large signal voltage gain is the total output swing divided by the input signal required to produce that swing. for v s = 15v, v out = 5v. for v s = +5v, v out = 1v. note 8: the open loop output current is the output swing with the 100 w load resistor divided by that resistor. note 9: slew rate is the average of the rising and falling slew rates. note 10: differential gain and phase are measured with a v = +2, v in = 1v pp at 3.58 mhz and both input and output 75 w terminated. note 11: differential input voltage is measured at v s = 15v. typical performance characteristics unless otherwise noted, t a = 25c supply current vs supply voltage ds012336-20 supply current vs temperature ds012336-21 input offset voltage vs temperature ds012336-22 input bias current vs temperature ds012336-23 input offset voltage vs common mode voltage ds012336-24 short circuit current vs temperature (sourcing) ds012336-25 www.national.com 6
typical performance characteristics unless otherwise noted, t a = 25c (continued) short circuit current vs temperature (sinking) ds012336-26 output voltage vs output current ds012336-27 output voltage vs output current ds012336-28 cmrr vs frequency ds012336-29 psrr vs frequency ds012336-30 psrr vs frequency ds012336-31 open loop frequency response ds012336-32 open loop frequency response ds012336-33 gain bandwidth product vs supply voltage ds012336-34 www.national.com 7
typical performance characteristics unless otherwise noted, t a = 25c (continued) gain bandwidth product vs load capacitance ds012336-35 large signal voltage gain vs load ds012336-36 large signal voltage gain vs load ds012336-37 input voltage noise vs frequency ds012336-38 input voltage noise vs frequency ds012336-39 input current noise vs frequency ds012336-40 input current noise vs frequency ds012336-41 slew rate vs supply voltage ds012336-42 slew rate vs input voltage ds012336-43 www.national.com 8
typical performance characteristics unless otherwise noted, t a = 25c (continued) slew rate vs load capacitance ds012336-44 open loop output impedance vs frequency ds012336-45 open loop output impedance vs frequency ds012336-46 large signal pulse response a v = ?1, v s = 15v ds012336-47 large signal pulse response a v = ?1, v s = 5v ds012336-48 large signal pulse response a v = +1, v s = 15v ds012336-49 large signal pulse response a v = +1, v s = 5v ds012336-50 large signal pulse response a v = +2, v s = 15v ds012336-51 large signal pulse response a v = +2, v s = 5v ds012336-52 www.national.com 9
typical performance characteristics unless otherwise noted, t a = 25c (continued) small signal pulse response a v = ?1, v s = 15v ds012336-53 small signal pulse response a v = ?1, v s = 5v ds012336-54 small signal pulse response a v = +1, v s = 15v ds012336-55 small signal pulse response a v = +1, v s = 5v ds012336-56 small signal pulse response a v = +2, v s = 15v ds012336-57 small signal pulse response a v = +2, v s = 5v ds012336-58 closed loop frequency response vs supply voltage (a v = +1) ds012336-59 closed loop frequency response vs supply voltage (a v = +2) ds012336-60 closed loop frequency response vs capacitive load (a v = +1) ds012336-61 www.national.com 10
typical performance characteristics unless otherwise noted, t a = 25c (continued) closed loop frequency response vs capacitive load (a v = +1) ds012336-62 closed loop frequency response vs capacitive load (a v = +2) ds012336-63 closed loop frequency response vs capacitive load (a v = +2) ds012336-64 total harmonic distortion vs frequency ds012336-65 total harmonic distortion vs frequency ds012336-66 total harmonic distortion vs frequency ds012336-67 total harmonic distortion vs frequency ds012336-68 undistorted output swing vs frequency ds012336-69 undistorted output swing vs frequency ds012336-70 www.national.com 11
typical performance characteristics unless otherwise noted, t a = 25c (continued) LM6171 simplified schematic application information LM6171 performance discussion the LM6171 is a high speed, unity-gain stable voltage feed- back amplifier. it consumes only 2.5 ma supply current while providing a gain-bandwidth product of 100 mhz and a slew rate of 3600v/s. it also has other great features such as low differential gain and phase and high output current. the LM6171 is a good choice in high speed circuits. the LM6171 is a true voltage feedback amplifier. unlike cur- rent feedback amplifiers (cfas) with a low inverting input im- pedance and a high non-inverting input impedance, both in- puts of voltage feedback amplifiers (vfas) have high impedance nodes. the low impedance inverting input in cfas will couple with feedback capacitor and cause oscilla- tion. as a result, cfas cannot be used in traditional op amp circuits such as photodiode amplifiers, i-to-v converters and integrators. LM6171 circuit operation the class ab input stage in LM6171 is fully symmetrical and has a similar slewing characteristic to the current feedback amplifiers. in the LM6171 simplfied schematic, q1 through q4 form the equivalent of the current feedback input buffer, r e the equivalent of the feedback resistor, and stage a buff- ers the inverting input. the triple-buffered output stage iso- lates the gain stage from the load to provide low output im- pedance. LM6171 slew rate characteristic the slew rate of LM6171 is determined by the current avail- able to charge and discharge an internal high impedance node capacitor. the current is the differential input voltage divided by the total degeneration resistor r e . therefore, the undistorted output swing vs frequency ds012336-71 undistorted output swing vs frequency ds012336-72 total power dissipation vs ambient temperature ds012336-73 ds012336-10 www.national.com 12
application information (continued) slew rate is proportional to the input voltage level, and the higher slew rates are achievable in the lower gain configura- tions. when a very fast large signal pulse is applied to the input of an amplifier, some overshoot or undershoot occurs. by plac- ing an external series resistor such as 1 k w to the input of LM6171, the bandwidth is reduced to help lower the over- shoot. layout consideration printed circuit boards and high speed op amps there are many things to consider when designing pc boards for high speed op amps. without proper caution, it is very easy and frustrating to have excessive ringing, oscilla- tion and other degraded ac performance in high speed cir- cuits. as a rule, the signal traces should be short and wide to provide low inductance and low impedance paths. any un- used board space needs to be grounded to reduce stray sig- nal pickup. critical components should also be grounded at a common point to eliminate voltage drop. sockets add ca- pacitance to the board and can affect frequency perfor- mance. it is better to solder the amplifier directly into the pc board without using any socket. using probes active (fet) probes are ideal for taking high frequency mea- surements because they have wide bandwidth, high input impedance and low input capacitance. however, the probe ground leads provide a long ground loop that will produce er- rors in measurement. instead, the probes can be grounded directly by removing the ground leads and probe jackets and using scope probe jacks. components selection and feedback resistor it is important in high speed applications to keep all compo- nent leads short because wires are inductive at high fre- quency. for discrete components, choose carbon composition-type resistors and mica-type capacitors. sur- face mount components are preferred over discrete compo- nents for minimum inductive effect. large values of feedback resistors can couple with parasitic capacitance and cause undesirable effects such as ringing or oscillation in high speed amplifiers. for LM6171, a feed- back resistor of 510 w gives optimal performance. compensation for input capacitance the combination of an amplifier's input capacitance with the gain setting resistors adds a pole that can cause peaking or oscillation. to solve this problem, a feedback capacitor with a value c f > (r g xc in )/r f can be used to cancel that pole. for LM6171, a feedback ca- pacitor of 2 pf is recommended. figure 1 illustrates the com- pensation circuit. power supply bypassing bypassing the power supply is necessary to maintain low power supply impedance across frequency. both positive and negative power supplies should be bypassed individu- ally by placing 0.01 f ceramic capacitors directly to power supply pins and 2.2 f tantalum capacitors close to the power supply pins. termination in high frequency applications, reflections occur if signals are not properly terminated. figure 3 shows a properly termi- nated signal while figure 4 shows an improperly terminated signal. ds012336-11 figure 1. compensating for input capacitance ds012336-12 figure 2. power supply bypassing ds012336-14 figure 3. properly terminated signal www.national.com 13
application information (continued) to minimize reflection, coaxial cable with matching charac- teristic impedance to the signal source should be used. the other end of the cable should be terminated with the same value terminator or resistor. for the commonly used cables, rg59 has 75 w characteristic impedance, and rg58 has 50 w characteristic impedance. driving capacitive loads amplifiers driving capacitive loads can oscillate or have ring- ing at the output. to eliminate oscillation or reduce ringing, an isolation resistor can be placed as shown below in figure 5 . the combination of the isolation resistor and the load ca- pacitor forms a pole to increase stablility by adding more phase margin to the overall system. the desired perfor- mance depends on the value of the isolation resistor; the big- ger the isolation resistor, the more damped the pulse re- sponse becomes. for LM6171, a 50 w isolation resistor is recommended for initial evaluation. figure 6 shows the LM6171 driving a 200 pf load with the 50 w isolation resistor. power dissipation the maximum power allowed to dissipate in a device is de- fined as: p d = (t j(max) ?t a )/ q ja where p d is the power dissipation in a device t j(max) is the maximum junction temperature t a is the ambient temperature q ja is the thermal resistance of a particular package for example, for the LM6171 in a so-8 package, the maxi- mum power dissipation at 25c ambient temperature is 730 mw. thermal resistance, q ja , depends on parameters such as die size, package size and package material. the smaller the die size and package, the higher q ja becomes. the 8-pin dip package has a lower thermal resistance (108c/w) than that of 8-pin so (172c/w). therefore, for higher dissipation capability, use an 8-pin dip package. ds012336-15 figure 4. improperly terminated signal ds012336-13 figure 5. isolation resistor used to drive capacitive load ds012336-16 figure 6. the LM6171 driving a 200 pf load with a 50 w isolation resistor www.national.com 14
application information (continued) the total power dissipated in a device can be calculated as: p d = p q +p l p q is the quiescent power dissipated in a device with no load connected at the output. p l is the power dissipated in the de- vice with a load connected at the output; it is not the power dissipated by the load. furthermore, p q = supply current x total supply voltage with no load p l = output current x (voltage difference between supply voltage and output voltage of the same supply) for example, the total power dissipated by the LM6171 with v s = 15v and output voltage of 10v into 1 k w load resistor (one end tied to ground) is p d = p q +p l = (2.5 ma) x (30v) + (10 ma) x (15v ? 10v) = 75mw+50mw = 125 mw application circuits design kit a design kit is available for the LM6171. the design kit con- tains: high speed evaluation board LM6171 in 8-pin dip package LM6171 datasheet pspice macromodel diskette with the LM6171 macro- model an amplifier selection guide pitch pack a pitch pack is available for the LM6171. the pitch pack con- tains: high speed evaluation board LM6171 in 8-pin dip package LM6171 datasheet pspice macromodel diskette with the LM6171 macro- model contact your local national semiconductor sales office to obtain a pitch pack. fast instrumentation amplifier ds012336-17 multivibrator ds012336-18 pulse width modulator ds012336-19 www.national.com 15
physical dimensions inches (millimeters) unless otherwise noted 8-pin small outline package ns package number m08a 8-pin molded dip package ns package number n08e www.national.com 16
notes life support policy national's products are not authorized for use as critical components in life support devices or systems without the express written approval of the president of national semiconductor corporation. as used herein: 1. life support devices or systems are devices or systems which, (a) are intended for surgical implant into the body, or (b) support or sustain life, and whose failure to perform when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a significant injury to the user. 2. a critical component is any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system, or to affect its safety or effectiveness. national semiconductor corporation americas tel: 1-800-272-9959 fax: 1-800-737-7018 email: support@nsc.com national semiconductor europe fax: +49 (0) 1 80-530 85 86 email: europe.support@nsc.com deutsch tel: +49 (0) 1 80-530 85 85 english tel: +49 (0) 1 80-532 78 32 fran?ais tel: +49 (0) 1 80-532 93 58 italiano tel: +49 (0) 1 80-534 16 80 national semiconductor asia pacific customer response group tel: 65-2544466 fax: 65-2504466 email: sea.support@nsc.com national semiconductor japan ltd. tel: 81-3-5639-7560 fax: 81-3-5639-7507 www.national.com LM6171 high speed low power low distortion voltage feedback amplifier national does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and national reserves the righ t at any time without notice to change said circuitry and specifications.

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