ICS9248-39
Frequency Generator & Integrated Buffers for PENTIUM/ProTM
General Description
The ICS9248-39 generates all clocks required for high
speed RISC or CISC microprocessor systems such as
Intel PentiumPro or Cyrix. Eight different reference
frequency multiplying factors are externally selectable
with smooth frequency transitions.
Features include two CPU, six PCI and thirteen SDRAM
clocks. Two reference outputs are available equal to the
crystal frequency. Plus the IOAPIC output powered by
VDDL1. One 48 MHz for USB, and one 24 MHz clock for
Super IO. Spread Spectrum built in at ±0.5% or ±0.25%
modulation to reduce the EMI. Serial programming I2C
interface allows changing functions, stop clock programing
and Frequency selection. Additionally, the device meets
the Pentium power-up stabilization, which requires that
CPU and PCI clocks be stable within 2ms after power-up.
It is not recommended to use I/O dual function pin for the
slots (ISA, PIC, CPU, DIMM). The add on card might have
a pull up or pull down.
Features
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3.3V outputs: SDRAM, PCI, REF, 48/24MHz
2.5V outputs: CPU, IOAPIC
20 ohm CPU clock output impedance
20 ohm PCI clock output impedance
Skew from CPU (earlier) to PCI clock - 1.5 to 4 ns,
center 2.6 ns.
No external load cap for CL=18pF crystals
±175 ps CPU clock skew
250ps (cycle to cycle) CPU jitter
Smooth frequency switch, with selections from 66.8
to 150 MHz CPU.
I2C interface for programming
3ms power up clock stable time
Clock duty cycle 45-55%.
48 pin 300 mil SSOP package
3.3V operation, 5V tolerant inputs (with series R)
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