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M902-01I156.2500 Datasheet(PDF) 4 Page - Integrated Circuit Systems |
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M902-01I156.2500 Datasheet(HTML) 4 Page - Integrated Circuit Systems |
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4 / 8 page  M902-01 Datasheet Rev 2.1 4 of 8 Revised 24Jun2004 I n te g r at ed C i rcui t Syste m s , Inc. ● Ne tw or kin g & C o mmun ica t io ns ● ww w. ic st.c om ● tel (5 08 ) 8 52-5 4 0 0 Integrated Circuit Systems, Inc. M902-01 VCSO BASED GBE CLOCK GENERATOR Prod uct Data Sh eet APPLICATION INFORMATION This section includes information on the optional external crystal and on the external loop filter. The subsections on the loop filter provide example component values and also briefly describe the SAW PLL simulator tool and additional application information available at www.icst.com. External Crystal Specifications If an external crystal is used with the on-chip crystal oscillator circuit (XTAL OSC), the external crystal should have the following general specifications: The external crystal will be applied to the XTAL_1 / REF_IN and XTAL_2 input pins. External crystal load capacitors are also required. Recommended External Crystal Configuration Figure 4: Recommended External Crystal Configuration XTAL= 25 or 30 MHz, Load Capacitance Specification = 18 pF C1 = 27 pF C2 = 33 pF External load capacitors C1 and C2 present a load of 15 pf to the crystal (they are seen in series by the crystal through the common ground connection). With the additional of PCB trace capacitance and M902-01 input capacitance, the total load to the crystal is about 18 pf. External Loop Filter To provide stable PLL operation, and thereby a low jitter output clock, the M902-01 requires the use of an external loop filter. This is provided via the provided filter pins (see Figure 5). Figure 5: External Loop Filter The loop filter is implemented as a differential circuit to minimize system noise interference. Due to the differential signal path design, the implementation requires two identical complementary RC filters as shown here. See Table 4, External Loop Filter Component Values, below. Refer to the M902-01 product web page at www.icst.com/products/summary/m902-01.htm for additional product information. Crystal Specifications Parameter Min Typ Max Unit Crystal Type AT-cut quartz Mode of Oscillation Fundamental f0 Nominal Frequency Range 16 40 MHz ∆f/f0 Frequency Tolerance @+25 oC 1 Note 1: These frequency tolerance specifications are suitable for a ±100 ppm clock output frequency requirement. ±15 ppm ∆f/f C / TA Frequency Stability -40 to +85 oC 1 ±50 ppm ∆f/f0 / y Aging, per year (first) @+25 oC 1 ±5 ppm ESR Equivalent Series Resistance 50 Ω C S Shunt Capacitance 7 pF Spurious Response (non-harmonic) -40 dBc C L Load Capacitance, parallel load resonant 16 32 pF P0 Drive Level 0.1 1.0 mW Table 3: External Loop Filter Component Values XTAL_2 XTAL XTAL OSC M9xx-0x XTAL_1 / REF_IN C1 C2 M902-01 External Loop Filter Component Values PLL Bandwidth (kHz) Damping Factor R loop (k Ω) C loop ( µF) R post (k Ω) C post (pF) 0.5 3.0 1.5 4.70 20 150 1.5 1 Note 1: Optimum loop bandwidth when using an external reference crystal. Will help to attenuate interference on the crystal’s sinusoidal clock waveform and therefore will minimize device output clock jitter. 3.3 4.7 1.00 10 150 2.1 2 Note 2: Alternative loop filter setting when using an external refer- ence crystal. Smaller C loop lowers loop damping factor with negligible increase in output jitter. 1.1 4.7 0.10 10 150 6.4 4.5 20.0 0.10 20 270 10.6 3 Note 3: Optimum loop bandwidth when using an external reference crystal oscillator. The square wave clock reference does not require as much jitter attenuation, which allows for a wider loop bandwidth and improved system noise tolerance. 4.2 33.0 0.03 20 120 Table 4: External Loop Filter Component Values C POST C POST VC nVC R POST nOP_OUT OP_OUT R POST R LOOP R LOOP C LOOP C LOOP OP_IN nOP_IN 6 7 5 49 8 |
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