ICS9248-81 Datasheet | Integrated Circuit Systems

Integrated Circuit Systems, Inc. ICS9248- 81 Frequency Generator & Integrated Buffers General Description The ICS9248-81 is the single chip clock solution for Desktop/ Notebook designs using the SIS style chipset. It provides all necessary clock signals for such a system. Spread spectrum may be enabled through I2C programming. Spread spectrum typically reduces system EMI by 8d B to 10d B. This simplifies EMI qualification without resorting to board design iterations or costly shielding. The ICS9248-81 employs a proprietary closed loop design, which tightly controls the percentage of spreading over process and temperature variations. Serial programming I2C interface allows changing functions, stop clock programming and frequency selection. The SD_SEL latched input allows the SDRAM frequency to follow the CPUCLK frequency(SD_SEL=1) or other clock frequencies (SD_SEL=0) Features • Generates the following system clocks: - 3 CPU(2.5V/3.3V) up to 133.3MHz. - 6 PCI(3.3V) (including 1 free-running) - 13 SDRAMs(3.3V) up to 133.3MHz. - 3 REF (3.3V) @ 14.318MHz - 1 clock @ 24/14.3 MHz selectable output for SIO - 1 Fixed clock at 48MHz (3.3V) - 1 IOAPIC @ 2.5V / 3.3V Skew characteristics: - CPU – CPU<175ps - SDRAM – SDRAM < 250ps - CPU–SDRAM < 500ps - CPU(early) – PCI : 1-4ns (typ. 3ns) - PCI – PCI <500ps Supports Spread Spectrum modulation ±0.25 & ±0.5% center spread Serial I2C interface for Power Management, Frequency Select, Spread Spectrum. Efficient Power management scheme through PCI, SDRAM, CPU STOP CLOCKS and PD#. Uses external 14.318MHz crystal 48 pin 300mil SSOP. • • • • • • Block Diagram Pin Configuration Power Groups VDDREF = REF [2:0], X1, X2 VDDPCI = PCICLK_F, PCICLK [4:0] VDDSD/C = SDRAM [11:0], supply for PLL core, 24 MHz, 48MHz VDD/CPU = CPUCLK [3:1] VDDLAPIC = IOAPIC GNDFIX = Ground for fixed clock PLL and output buffers 9248-81 Rev E 10/12/99 48-Pin SSOP - Internal Pull-up Resistor of 120K to 3.3V on indicated inputs Pentium is a trademark of Intel...