Datasheet 5L1503 (IDT) - 9

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Spread Spectrum Spread Spectrum
The 5L1503 supports spread spectrum clocks from PLL with digital spread spectrum.
Digital Spread Spectrum Figure 5. Digital Spread Spectrum
Step_deepth: step Fvco N  2 * Fout How many steps: Period Fpfd period  2 * Fss N * SSamount step  period
Down spread or spread off
N = Fvco/Fpfd N: include integer and fraction Fvco: VCOs frequency Fpfd: PLLs pfd frequency Fss: spread modulation rate SSamount: spread percentage N will decrease to make the center frequency lower than spread off.
Example
: 0.5% down spread at 32kHz modulation rate.
Reference Input and Selection
The 5L1503 accepts an 8MHz–40MHz crystal input or 1MHz–100MHz LVCMOS (to X1) input. See the Crystal Oscillator Reference Circuit for details.
Crystal Input (X1/X2)
The crystal oscillators should be fundamental mode quartz crystals; overtone crystals are not suitable. Crystal frequency should be specified for parallel resonance with 54MHz maximum. A crystal manufacturer wil calibrate its crystals to the nominal frequency with a certain load capacitance value. When the oscillator load capacitance matches the crystal load capacitance, the oscillation frequency wil be accurate as 0 PPM. When the oscil ator load capacitance is lower than the crystal load capacitance, the oscillation frequency wil be higher than nominal. In order to get an accurate oscil ation frequency, the matching the oscillator load capacitance with the crystal load capacitance is required. To set the oscil ator load capacitance, 5L1503 has built-in two programmable tuning capacitors inside the chip, one at XIN and one at XOUT. They can not be adjusted independently, The value of each capacitor is composed of a fixed capacitance amount plus a variable capacitance amount set with the XTAL_CAP[3:0] register. Adjustment of the crystal tuning capacitors allows for maximum flexibility to accommodate crystals from various manufacturers. The approximate range of tuning capacitor values available are in accordance with the following table. ©2019 Integrated Device Technology, Inc 9 June 19, 2019 Document Outline Description Typical Applications Features Output Features Key Specifications Block Diagram Pin Assignments Figure 1. Pin Assignments for 2.0 × 2.0 mm 10-VFQFPN Package Pin Descriptions Table 1. Pin Descriptions Device Feature and Function DFC – Dynamic Frequency Control Figure 2. DFC Function Block Diagram Table 2. DFC Function Priority DFC Function Programming PPS – Proactive Power Saving Function Figure 3. PPS Function Block Diagram Figure 4. PPS Assertion/Deassertion Timing Chart PPS Function Programming Output Divider Selection Table 3. Output Divider Selection Device Output Support 5L1503 5L1503L 5L1503S OE Pin Function Table 4. OE Pin Function Table 5. OE Pin Function Summary Table 6. PD# Priority Spread Spectrum Spread Spectrum Digital Spread Spectrum Figure 5. Digital Spread Spectrum Reference Input and Selection Crystal Input (X1/X2) Table 7. Programmable Tuning Capacitors Figure 6. Crystal Oscillator Reference Circuit Absolute Maximum Ratings Table 8. Absolute Maximum Ratings Thermal Characteristics Table 9. Thermal Characteristics Recommended Operating Conditions Table 10. Recommended Operating Conditions Crystal Characteristics Table 11. Crystal Characteristics DC Electrical Characteristics Table 12. DC Electrical Characteristics – Current Table 13. DC Electrical Characteristics – Input and Output Voltage AC Electrical Characteristics Table 14. AC Timing Electrical Characteristics I2C Bus DC Characteristics Table 15. I2C Bus DC Characteristics Table 16. I2C Bus AC Characteristics Spread Spectrum Generation Specifications Table 17. Spread Spectrum Generation Specifications (5L1503S only) General I2C Interface Information How to Write How to Read Glossary of Features Table 18. Glossary of Features Package Outline Drawings Ordering Information Marking Diagrams Revision History