View LCK4950_6796210.PDF datasheet online --- IC-ON-LINE

Datasheet File OCR Text:

data sheet january 2002 LCK4950 low-voltage pll clock driver features fully integrated phase-locked loop (pll) oscillator or crystal reference input output frequency up to 180 mhz outputs disable in high impedance compatible with powerpc ? , intel ? , and high- performance risc microprocessors tqfp packaging output frequency configurable 35 ps typical cycle-to-cycle jitter pin compatible with the motorola ? mpc950 clock driver description the LCK4950 is a pll-based clock driver device intended for high-performance clock tree designs. the LCK4950 is 3.3 v compatible with output frequencies of up to 180 mhz and output skews of 200 ps. the LCK4950 can accommodate the most demanding tree designs by employing a fully differential pll design. this minimizes cycle-to-cycle jitter, which is critical when the device is acting as the reference clock for plls in today ? s microprocessors and asics. the device has nine low-skew configurable outputs for support of the clocking needs of the various high-performance microprocessors. to provide input reference clock flexibility, two selectable division ratios are available on the LCK4950. the internal v co runs at either 2x or 4x the high-speed output. the fbsel pin is used to select between a divide by 8 or a divide by 16 of the v co frequency to be compared with the input reference. these selections allow the input reference to be either one-half, one-fourth, or one-eighth of the high-speed output. the LCK4950 is capable of scan clock distribution or system diagnostics due to an external test clock input. the ref_sel pin allows the selection between a crystal input to an on-chip oscillator for the reference or selection of a ttl level oscillator input directly. only a parallel resonant crystal is required for the onboard crystal oscillator external components. the LCK4950 is fully 3.3 v compatible and requires no external loop filter components. all inputs accept lvcmos or lvttl compatible levels while the outputs provide lvcmos levels with the capability to drive terminated 50 ? transmission lines. the LCK4950 can drive two traces, giving the device an effective fan out of 1:18 for series-terminated 50 ? lines. for optimum performance and board density, the device is packaged in a 7 mm x 7 mm 32-lead tqfp package.
2 agere systems inc. data sheet january 2002 low-voltage pll clock driver LCK4950 description (continued) 5-9698 (f) figure 1. logic diagram fsela pll_en tclk ref_sel xtal1 xtal2 fbsel (pull-down) fselb fselc mr/oe fseld power-on reset 4/ 8 4/ 8 4/ 8 2/ 4 qa qb qc0 qc1 qd0 qd1 qd2 qd3 qd4 (v co ) 200 mhz ? 480 mhz phase detector lpf 8/ 16 xtal osc
agere systems inc. 3 data sheet january 2002 low-voltage pll clock driver LCK4950 pin information 5-9699 (f) figure 2. pin diagram functional description table 1. function tables ref_sel function 1tclk 0xtal_osc pll_en function 1 pll enabled 0 pll bypass fbsel function 1 8 0 16 mr/oe function 1 outputs disabled 0 outputs enabled fseln function 1qa = 4; qb:d = 8 0qa = 2; qb:d = 4 LCK4950 25 26 27 28 29 30 31 32 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 17 18 19 20 21 22 23 24 v ss qb v dd qa v ss tclk pll_en ref_sel v ss qd1 v dd qd0 v ss qc1 v dd qc0 qd2 v dd qd3 v ss qd4 v dd mr/oe xtal2 xtal1 v ss fseld fselc fselb fsela fbsel v dda
4 4 agere systems inc. data sheet january 2002 low-voltage pll clock driver LCK4950 functional description (continued) table 2. function table note: x = fvco/4; 200 mhz < fvco < 480 mhz. table 3. pll input reference characteristics * maximum and minimum input reference is limited by the v co lock range and the feedback divider for the tclk or xtal1 inputs. ? see the applications section for more crystal information. inputs outputs totals fsela fselb fselc fseld qa(1) qb(1) qc(2) qd(5) total 2x total x total x/2 00002xxxx180 00012xxxx/2135 00102xxx/2x162 00112xxx/2x/2117 01002xx/2xx171 01012xx/2xx/2126 01102xx/2x/2x135 01112xx/2x/2x/2108 1000 xxxx090 1001xxxx/2045 1010xxx/2x072 1011xxx/2x/2027 1100xx/2xx081 1101xx/2xx/2036 1110xx/2x/2x063 1111xx/2x/2x/2018 characteristic symbol min max unit tclk input rise/falls t r , t f ? 3.0 ns reference input frequency f ref ? * ? *mhz crystal oscillator frequency ? f xtal 12.5 25 mhz reference input duty cycle f refdc 25 75 %
agere systems inc. 5 data sheet january 2002 low-voltage pll clock driver LCK4950 applications programming the LCK4950s several frequency relationships are configurable by the LCK4950. frequency ratios of 1:1, 2:1, 4:1, and 4:2:1 are possible from configuring the output dividers for the four output groups. to ensure that the output duty cycle is always 50%, the LCK4950 uses even dividers. table 4 illustrates output configurations of the LCK4950, describing the outputs using the v co frequency as a reference. for example, setting the qa outputs to v co /2, the qb and qc to v co /4, and the qd to v co /8 would provide the output frequency relationship of 4:2:1. table 4. programmable output frequency relationships the division settings establish the output relationship, but one must still ensure that the v co will be stable given the frequency of the outputs desired. the feedback frequency should be used to situate the v co into a frequency range in which the pll will be stable. the design of the pll is such that for output frequencies between 25 mhz and 180 mhz, the LCK4950 can generally be configured into a stable region. inputs outputs fsela fselb fselc fseld qa qb qc qd 0000v co /2 v co /4 v co /4 v co /4 0001v co /2 v co /4 v co /4 v co /8 0010v co /2 v co /4 v co /8 v co /4 0011v co /2 v co /4 v co /8 v co /8 0100v co /2 v co /8 v co /4 v co /4 0101v co /2 v co /8 v co /4 v co /8 0110v co /2 v co /8 v co /8 v co /4 0111v co /2 v co /8 v co /8 v co /8 1000v co /4 v co /4 v co /4 v co /4 1001v co /4 v co /4 v co /4 v co /8 1010v co /4 v co /4 v co /8 v co /4 1011v co /4 v co /4 v co /8 v co /8 1100v co /4 v co /8 v co /4 v co /4 1101v co /4 v co /8 v co /4 v co /8 1110v co /4 v co /8 v co /8 v co /4 1111v co /4 v co /8 v co /8 v co /8
6 6 agere systems inc. data sheet january 2002 low-voltage pll clock driver LCK4950 applications (continued) table 5. input reference vs. output frequency relationships the relationship between the input reference and the output frequency is very flexible. table 5 shows the multiplication factors between the inputs and outputs for the LCK4950. figure 3 through figure 6 illustrate several programming possibilities. note: the variations of the configurations shown are not complete, but do represent potential applications. config fsela fselb fselc fseld fb_sel = 1 fb_sel = 0 qa qb qc qd qa qb qc qd 1 0 0 0 0 4x 2x 2x 2x 8x 4x 4x 4x 2 0 0 0 1 4x2x2x x 8x4x4x2x 3 0 0 1 0 4x2x x 2x8x4x2x4x 4 0 0 1 1 4x 2x x x 8x 4x 2x 2x 5 0 1 0 0 4x x 2x2x8x2x4x4x 6 0 1 0 1 4x x 2x x 8x 2x 4x 2x 7 0 1 1 0 4x x x 2x 8x 2x 2x 4x 8 0 1 1 1 4x x x x 8x2x2x2x 9 1 0 0 0 2x 2x 2x 2x 4x 4x 4x 4x 10 1 0 0 1 2x2x2x x 4x4x4x2x 11 1 0 1 0 2x2x x 2x4x4x2x4x 12 1 0 1 1 2x 2x x x 4x 4x 2x 2x 13 1 1 0 0 2x x 2x2x4x2x4x4x 14 1 1 0 1 2x x 2x x 4x 2x 4x 2x 15 1 1 1 0 2x x x 2x 4x 2x 2x 4x 16 1 1 1 1 2x x x x 4x2x2x2x
agere systems inc. 7 data sheet january 2002 low-voltage pll clock driver LCK4950 applications (continued) 5-9700 (f) figure 3. dual-frequency configuration 5-9701 (f) figure 4. dual-frequency configuration 66.66 mhz 33.33 mhz 33.33 mhz 66.66 mhz fsela fselb fselc fseld fbsel qd qc qb qa input ref 16.66 mhz 0 0 1 1 1 1 1 2 5 33.33 mhz 66.66 mhz 66.66 mhz 66.66 mhz fsela fselb fselc fseld fbsel qd qc qb qa input ref 33.33 mhz 1 1 1 0 0 1 1 2 5 5-9702 (f) figure 5. dual-frequency configuration 5-9703 (f) figure 6. triple-frequency configuration 33.33 mhz 33.33 mhz 33.33 mhz 66.66 mhz fsela fselb fselc fseld fbsel qd qc qb qa input ref 16.66 mhz 0 0 1 1 1 1 1 2 5 40 mhz 40 mhz 80 mhz 160 mhz fsela fselb fselc fseld fbsel qd qc qb qa input ref 20 mhz 0 1 0 0 1 1 1 2 5 absolute maximum ratings stresses in excess of the absolute maximum ratings can cause permanent damage to the device. these are absolute stress ratings only. functional operation of the device is not implied at these or any other conditions in excess of those given in the operational sections of the data sheet. exposure to absolute maximum ratings for extended periods can adversely affect device reliability. table 6. absolute maximum ratings parameter symbol min max unit supply voltage v dd , v dda ? 0.3 4.6 v input voltage v i ? 0.3 v dd + 0.3 v input current i in ? 20 ma storage temperature range t stor ? 40 125 c
8 8 agere systems inc. data sheet january 2002 low-voltage pll clock driver LCK4950 electrical characteristics table 7. dc characteristics t a = 0 c to 70 c, v cc = 3.3 v 5%. table 8. ac characteristics t a = 0 c to 70 c, v cc = 3.3 v 5%. characteristic symbol min typ max unit condition input high voltage (lvcmos inputs) v ih 2.0 ? 3.6 v ? input low voltage (lvcmos inputs) v il ?? 0.8 v ? output high voltage v oh 2.4 ?? v i oh = ? 40 ma 1 1. the LCK4950 outputs can drive series or parallel-terminated 50 ? (or 50 ? to v cc /2) transmission lines on the incident edge. output low voltage v ol ?? 0.5 v i ol = 40 ma 1 input current i in ?? 120 a ? input capacitance c in ?? 4pf ? power dissipation capacitance c pd ? 25 ? pf per output maximum quiescent supply current non-pll i ddq ?? 1maall v dd pins except v dda 2 2. total power = (i ddpll + i ddq ) x v + (fqacqa + fqbcqb + fqc0cqc0 + fqc1cqc1 + fqd0cqd0 + fqd1cqd1 + fqd2cqd2 + fqd3cqd3 + fqd4cqd4) x v 2 ; where v = v dd, cqa = load capacitance on qa, cqb = load capacitance on qb, etc. maximum pll supply current i ddpll ?? 55 ma v dda pin only characteristic symbol min typ max unit condition output rise/fall time t r , t f 0.10 ? 1.0 ns 0.8 v to 2.0 v output duty cycle t pw 48.5 ? 51.5 % ? same frequencies output-to-output skews t sk(0) ? 150 300 ps ? different frequencies: qa fmax < 150 mhz qa fmax > 150 mhz ? ? 200 ? 400 400 ps ps ? ? pll v co (feedback = v co /4) lock (feedback = v co /8) range (feedback = v co /16) f vco 200 200 200 ? ? ? 480 480 480 mhz mhz mhz ? ? ? maximum output frequency: qa( 2) qa/qb ( 4) qb ( 8) f max ? ? ? ? ? ? 180 120 60 mhz mhz mhz ? ? ? output disable time t plz,hz ?? 7ns ? output enable time t pzl ?? 6ns ? cycle-to-cycle jitter (peak-to-peak) t jitter ? 35 50 ps ? 1 1.see applications section for more information. maximum pll clock time t lock ?? 10 ms ?
agere systems inc. 9 data sheet january 2002 low-voltage pll clock driver LCK4950 electrical characteristics (continued) jitter performance of the LCK4950s more focus is given to clock distribution design and management today because of the continuing increase of today ? s digital system ? s clock rates. system-clock jitter and its effect on overall system timing budget is at the center of this focus. the LCK4950 is designed to utilize a differential cmos pll and incorporate multiple power and ground pins in the design to minimize clock jitter. the following text provides details on the jitter performance, illustrates measurement limitations, and provides guidelines to minimize the jitter of the LCK4950. the most commonly specified jitter parameter is cycle-to-cycle jitter. with today ? s high-performance measurement equipment, there is no way to measure this parameter for jitter performance in the class demonstrated by the LCK4950. as a result, different methods are used which approximate cycle-to-cycle jitter. the typical method of measuring the jitter is to accumulate a large number of cycles, create a histogram of the edge placements, and record peak-to-peak as well as standard deviations of the jitter. it is of great importance to measure the edge immediately following the trigger edge. if this is not the case, the measurement inaccuracy will add significantly to the measured jitter. the oscilloscope cannot collect adjacent pulses. it is safe to assume that collecting pulse information in this mode will produce jitter values somewhat larger than if consecutive cycles were measured; therefore, this measurement will represent an upper bound of cycle-to-cycle jitter. most likely, this is a conservative estimate of the cycle-to-cycle jitter. there are two common sources of jitter for a pll-based clock driver. the most common source of jitter is random jitter. less commonly known is the jitter produced by different frequency outputs switching synchronously. if all of the outputs are switching at the same frequency, the pll jitter is equal to the total jitter of the device. in the LCK4950, where a number of the outputs can be switching synchronously but at different frequencies, a multimodal jitter distribution can be seen on the highest frequency outputs. it is important to consider what is happening on the other outputs because the output being monitored is affected by the activity on the other outputs. from figure 7, one can see that for each rising edge on the higher-frequency signal, the activity on the lower- frequency signal is not consistent. the placement of the edge that is being monitored is displaced in time due to the activity on the other outputs altering the internal thresholds of the device. the relationship is periodic because the signals are synchronous. the resulting jitter is a superposition of the pll jitter on the displaced edges. the multimodal distribution will appear to be a fat gaussian distribution, or a truly multimodal distribution depending on the size of the pll jitter and displacement of the edges. when all the outputs are switching at the same frequency, there is no edge displacement and the jitter is that of the pll.
10 10 agere systems inc. data sheet january 2002 low-voltage pll clock driver LCK4950 electrical characteristics (continued) 5-9704 (f) figure 7. pll jitter and edge displacement 1 22 1 1 22 3 123 1 2 peak-to-peak pll jitter peak-to-peak period jitter peak-to-peak pll jitter peak-to-peak period jitter 123
agere systems inc. 11 data sheet january 2002 low-voltage pll clock driver LCK4950 electrical characteristics (continued) 5-9707 (f) figure 8. power supply filter pll jitter can be measured for configurations where the outputs are switching at different frequencies by triggering the lowest-frequency output. pll jitter is dependent on internal v co frequency more so than output configuration. there are some general guidelines that will minimize the output jitter of the device. first, always configure the device so the v co runs as fast as possible. this is the most important aspect in minimizing jitter of the LCK4950. second, maintain the reference frequency at the highest possible frequency. these more frequent phase detector updates help to reduce jitter. there is a trade-off between higher reference frequencies and higher v co frequency; always choose a higher v co frequency to reduce jitter. third, and the most difficult to follow, minimize the number of different frequencies sourced from a single chip. the fixed edge displacement associated with the switching noise, in most cases, nearly doubles the effective jitter of a high- speed output. power supply filtering the LCK4950 exhibits some sensitivities that would not be seen on a fully digital product because the LCK4950 is a mixed analog/digital product. analog circuitry is naturally sensitive to random noise, most noticeably when the noise is in the power supply pins. the LCK4950 provides a separate output buffer power supply (v dd ) and phase-locked loop (v dda ) power supply pins. this design isolates the high switching noise digital outputs from the sensitive internal analog phase-locked loop. in a controlled setup (i.e., an evaluation board), this amount of isolation will suffice. in a digital system, where it is much more difficult to minimize noise on the power supplies, an additional level of isolation may be required. the easiest means of accomplishing this is by applying a power supply filter on the v dda pin for the LCK4950. figure 8 illustrates a typical power supply filter scheme for the LCK4950. the device is most greatly affected by spectral content in the 1 khz to 1 mhz range, and therefore needs a filter to target this range. the most important aspect of this final filter design is the dc voltage drop between the v dd supply and v dda pin. the i ddpll current (current forced through the v dda pin) is normally 45 ma (55 ma maximum), assuming that a minimum of 3.0 v must be maintained on the v dda pin. very little voltage drop can be tolerated when a 3.3 v v dd supply is used. the resistor shown in figure 10 must have a resistance of 5 ? ? 10 ? to meet the voltage drop criteria. the rc filter shown provides a broadband filter with about 100:1 attenuation for noise, with a spectral content above 20 khz. as the noise frequency crosses the series resonant point of an individual capacitor, its overall impedance begins to look inductive and therefore increases with increasing frequency. the parallel capacitor circuit shown in figure 11 guarantees that a low- impedance path to ground exists for frequencies exceeding the bandwidth of the pll. it is recommended that the user start with an 8 ? ? 10 ? resistor to avoid potential v dd drop problems and only use higher-value resistors when a higher level of attenuation is needed. the LCK4950 has several design features to minimize the susceptibility to power supply noise (isolated power and grounds and fully differential pll). still, there may be applications in which overall performance is being degraded due to system power supply noise. the power supply filter schemes discussed in this section should be adequate to eliminate power supply noise- related problems in most designs. 0.01 f 22 f r s = 5 ? ? 10 ? v cc pll_v cc LCK4950 0.01 f 3.3 v
12 agere systems inc. data sheet january 2002 low-voltage pll clock driver LCK4950 electrical characteristics (continued) using the on-chip crystal oscillator the LCK4950 features an on-chip crystal oscillator buffer to allow for seed clock generation as well as final distribution. the only external component required is the crystal since the on-chip oscillator buffer is completely self-contained. the user is advised to mount the crystal as close to the LCK4950 as possible to avoid board-level parasitics since the oscillator is, to a degree, sensitive to loading at the inputs. to facilitate collocation, surface- mount crystals are recommended, but not required. the oscillator circuit is a parallel resonant circuit with on-chip shunt capacitors. a parallel resonant crystal is simply a crystal that has been characterized in its parallel resonant mode. therefore, in the majority of cases, a parallel specified crystal or a series resonant crystal can be used with the LCK4950 with just a minor frequency error. typically, a series crystal used in a parallel resonant mode will exhibit an oscillatory frequency a few hundred ppm different than the specified value. for most processor implementations, a few hundred ppm translates into khz inaccuracies, a small enough level not to represent a major issue. the LCK4950 is a clock driver that was designed to generate outputs with programmable frequency relationships. as a result, the crystal input frequency is a function of the desired output frequency. to determine the crystal required to produce the desired output frequency for an application that utilizes internal feedback, the pll block diagram (figure 9) should be used. the p and the m values for the LCK4950 are also included in figure 9. the m values can be found in table 1 on page 3. table 9. crystal specifications parameter value crystal cut fundamental at cut resonance parallel resonance frequency tolerance 75 ppm at 25 c frequency/temperature stability 150 ppm at 0 c to 70 c operating range 0 c to 70 c shunt capacitors 10 pf ? 40 pf equivalent series resistance (esr) 50 ? to 80 ? max correction drive level 100 w aging 5 ppm/yr (first three years)
agere systems inc. 13 data sheet january 2002 low-voltage pll clock driver LCK4950 electrical characteristics (continued) 5-9708 (f) figure 9. pll block diagram note: for computations refer to the following equations: m = 8 (fbsel = 1), 16(fbsel = 0), p = 1 for the LCK4950 clock driver, the following will provide an example of how to determine the crystal frequency required for a given design. given: qa = 160 mhz qb = 80 mhz qc = 40 mhz qd = 40 mhz fbsel = 0 (eq. 1) from figure 3: fqd = v co /8 then n = 8 or fqa = v co /2 then n = 2 from figure 9: m = 16 and p = 1 or phase detector lpf v co p n m qn f ref f f vco m -------------- f vco fq = , = f ref fqn n p ? ? m ----------------------------- - = f ref fqn n p ? ? m ----------------------------- - = t ref 4081 ? ? 16 ------------------------ 20 mhz = = t ref 16021 ? ? 16 --------------------------- - 20 mhz = =
14 agere systems inc. data sheet january 2002 low-voltage pll clock driver LCK4950 electrical characteristics (continued) driving transmission lines the LCK4950 clock driver was designed to drive high-speed signals in a terminated transmission line environment. the output drivers were designed to exhibit the lowest impedance possible to provide the optimum flexibility to the user. with an output impedance of less than 10 ?, the drivers can drive either parallel-terminated or series- terminated transmission lines. point-to-point distribution of signals is the method of choice in most high-performance clock networks. in a point-to- point scheme, either series-terminated or parallel-terminated transmission lines can be used. the parallel technique terminates the signal at the end of the line with a 50 ? resistance to v dd /2. only a single terminated line can be driven by each output of the LCK4950 clock driver because this technique draws a fairly high level of dc current. for the series driven case, however, there is no dc current draw and the outputs can drive multiple series- terminated lines. figure 10 illustrates an output driving a single series-terminated line. 5-9709 (f) figure 10. single transmission line the situation in figure 11 should be used to better match the impedances when driving multiple lines. in this case, the series-terminating resistors are reduced so when the parallel combination is added to the output buffer impedance the line impedance is perfectly matched. 5-9710 (f) figure 11. optimized dual line termination in output 7 ? buffer r s = 43 ? z o = 50 ? outa output 7 ? buffer r s = 36 ? z o = 50 ? r s = 36 ? z o = 50 ?
agere systems inc. 15 data sheet january 2002 low-voltage pll clock driver LCK4950 outline diagram dimensions are in millimeters. 12-3076(f) pin #1 identifier zone 16 7.00 0.20 9.00 0.20 1 32 25 8 9 24 17 9.00 0.20 7.00 0.20 1.60 max seating plane detail a 0.10 1.40 0.05 0.80 typ 0.05/0.15 detail b detail b 0.30/0.45 0.20 m 0.09/0.200 detail a 0.45/0.75 gage plane seating plane 1.00 ref 0.25
powerpc is a registered trademark of international business machines corporation. intel is a registered trademark of intel corporation. motorola is a registerd trademark of motorola, inc. copyright ? 2002 agere systems inc. all rights reserved january 2002 ds02-099hsi (replaces ds02-033hsi) agere systems inc. reserves the right to make changes to the product(s) or information contained herein without notice. no liab ility is assumed as a result of their use or application. for additional information, contact your agere systems account manager or the following: internet: http://www.agere.com e-mail: docmaster@agere.com n. america: agere systems inc., 555 union boulevard, room 30l-15p-ba, allentown, pa 18109-3286 1-800-372-2447 , fax 610-712-4106 (in canada: 1-800-553-2448 , fax 610-712-4106) asia: agere systems hong kong ltd., suites 3201 & 3210-12, 32/f, tower 2, the gateway, harbour city, kowloon tel. (852) 3129-2000 , fax (852) 3129-2020 china: (86) 21-5047-1212 (shanghai), (86) 10-6522-5566 (beijing), (86) 755-695-7224 (shenzhen) japan: (81) 3-5421-1600 (tokyo), korea: (82) 2-767-1850 (seoul), singapore: (65) 778-8833 , taiwan: (886) 2-2725-5858 (taipei) europe: tel. (44) 7000 624624 , fax (44) 1344 488 045

▲Up To Search▲

Price & Availability of LCK4950

	To Download LCK4950 Datasheet File
If you can't view the Datasheet, Please click here to try to view without PDF Reader .