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rev. a a ad8391 information furnished by analog devices is believed to be accurate and reliable. however, no responsibility is assumed by analog devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. no license is granted by implication or otherwise under any patent or patent rights of analog devices. trademarks and registered trademarks are the property of their respective owners. one technology way, p.o. box 9106, norwood, ma 02062-9106, u.s.a. tel: 781/329-4700 www.analog.com fax: 781/326-8703 ?2003 analog devices, inc. all rights reserved. xdsl line driver 3v to 12 v with power-down product description the ad8391 consists of two parallel, low cost xdsl line drive amplifiers capable of driving low distortion signals while running on both 3 v to 12 v single-supply or equivalent dual-supply rails. it is primarily intended for use in single-supply xdsl systems where low power is essential, such as line powered and battery backup systems. each amplifier output drives more than 250 ma of current while maintaining C 82 dbc of sfdr at 100 khz on 12 v, outstanding performance for any xdsl cpe application. the ad8391 provides a flexible power-down feature consisting of a 1-pin digital control line. this allows biasing of the ad8391 to full power (logic 1), standby (logic three -state maintains low amplifier output impedance), and shutdown (logic 0 places amplifier outputs in a high impedance state). pwdn is refer- enced to C v s . fabricated on adi s high speed xfcb process, the high band width and fast slew rate of the ad8391 keep distortion to a minimum, while dissipating a minimum of power. the quiescent current of the ad8391 is low: 19 ma total static current draw. the ad8391 comes in a compact 8-lead soic t hermal coastline package and operates over the temperature range C 40 c to +85 c. fre quency ?khz upstream power ?10db/div 25 250 137.5 empty bin figure 1. upstream transit spectrum with empty bin at 45 khz; line power = 12.5 dbm into 100 ? pin configuration 8-lead soic (thermal coastline) in2 v mid ? s v out 2 1 2 3 4 in1 pwdn +v s v out 1 ad8391 v mid v s v s 8 7 6 5 features ideal xdsl line driver for vodsl or low power applications such as usb, pcmcia, or pci based customer premise equipment (cpe) high output voltage and current drive 340 ma output drive current low power operation 3 v to 12 v power supply range 1-pin logic controlled standby, shutdown low supply current of 19 ma (typical) low distortion ?2 dbc sfdr, 12 v p-p into differential 21 @ 100 khz 4.5 nv/ hz input voltage noise density, 100 khz out-of-band sfdr = ?2 dbc, 144 khz to 500 khz, z line = 100 , p line = 13.5 dbm high speed 40 mhz bandwidth (? db) 375 v/ s slew rate applications vodsl modems xdsl usb, pci, pcmcia cards line powered or battery backup xdsl modems
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rev. a ad8391 C C C C ja = 100 c/w. maximum power dissipation the maximum power that can be safely dissipated by the ad8391 is limited by the associated rise in junction temperature. the maximum safe junction temperature for a plastic encapsu- lated device is determined by the glass transition temperature of the plastic, approximately 150 c. temporarily exceeding this limit may cause a shift in parametric performance due to a change in the stresses exerted on the die by the package. to ensure proper operation, it is necessary to observe the maxi- mum power derating curve. ambient temperature e c 2.0 e50 maximum power dissipation e w 1.5 1.0 0.5 0 e40 e30 e20 e10 0 10 20 30 40 50 60 70 80 90 t j = 150 c 8-lead soic package figure 2. plot of maximum power dissipation vs. temperature ordering guide temperature package package model range description option AD8391AR ? 40 c to +85 c 8-lead soic r-8 AD8391AR ? reel ? 40 c to +85 c 8-lead soic r-8 AD8391AR ? reel7 ? 40 c to +85 c 8-lead soic r-8 AD8391AR ? eval evaluation board caution esd (electrostatic discharge) sensitive device. electrostatic charges as high as 4000 v readily accumulate on the human body and test equipment and can discharge without detection. although the ad8391 features proprietary esd protection circuitry, permanent damage may occur on devices subjected to high energy electrostatic discharges. therefore, proper esd precautions are recommended to avoid performance degradation or loss of functionality.
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rev. a ad8391 C C C C C C C C C v v gtzs tz s r g r out in f in = () () ++ where: g r r f g =+ 1 tz s r sc r f tt () = + 1() r g in mi = 1 125 recognizing that g r in << r f , and that the ? 3 db point is set when tz(s) = r f , one can see that the amplifier ? s bandwidth depends primarily on the feedback resistor. there is a value of r f below which the amplifier will be unstable, as the amplifier will have additional poles that will contribute excess phase shift. the optimum value for r f depends on the gain and the amount of peaking tolerable in the application. for more information about current feedback amplifiers, see adi ? s high speed design te chniques at www.analog.com/ technology/amplifierslinear/ designtools/evaluationboards/pdf/1.pdf .
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( ? ) vv v r so o l the total supply power can then be computed as: pvvv r iv tot s o o l qs = ? () + 4 1 2 2 || in this differential driver, v o is the voltage at the output of one amplifier, so 2 v o is the voltage across r l . r l is the total imped- ance seen by the differential driver, including any back termination. now, with two observations the integrals are easily evaluated. first, the integral of v o 2 is simply the square of the rms value of v o . second, the integral of |v o | is equal to the average rectified value of v o , sometimes called the mean average deviation, or mad. it can be shown that for a dmt signal, the mad value is equal to 0.8 times the rms value: pv rms v v rms r iv tot o s o l qs =+ 408 1 2 2 (. ? ) for the ad8391 operating on a single 12 v supply and delivering a total of 16 dbm (13 dbm to the line and 3 dbm to account for the matching network) into 50 (100 reflected back through a 1:2 transformer plus back termination), the dissipated power is 395 mw.
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rev. a ad8391 C C 1/4 inch stainless panhead machine screw ads #30-1-1 4# 4-40 3/4 inch-long aluminum round stand-off ads #30-16-3
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