Pentium®/II, 6x86, K6 Clock Synthesizer/Driver for Desktop PCs
with Intel 82430TX, 82440LX or ALI IV/IV+, AGP and 3 DIMMs
• Mixed 2.5V and 3.3V operation
• Complete clock solution for Pentium®, Pentium® II,
Cyrix, and AMD processor-based motherboards
— Four CPU clocks at 2.5V or 3.3V
— Up to twelve 3.3V SDRAM clocks
— Seven synchronous PCI clocks, one free-running
— One 3.3V 48 MHz USB clock
— One 2.5V IOAPIC clock (-3 option only)
— Two AGP clocks at 60 or 66.6MHz (-2 option only)
— One 3.3V Ref. clock at 14.318 MHz
C™ Serial Configuration Interface
• Factory-EPROM programmable output drive and slew
rate for EMI customization
• Factory-EPROM programmable CPU clock frequencies
for custom configurations
• Power-down, CPU stop and PCI stop pins
• Available in space-saving 48-pin SSOP package
The CY2273A possesses power-down, CPU stop, and PCI
stop pins for power management control. These inputs are
multiplexed with SDRAM clock outputs, and are selected when
the MODE pin is driven low. Additionally, the signals are syn-
chronized on-chip, and ensure glitch-free transitions on the
outputs. When the CPU_STOP input is asserted, the CPU
clock outputs are driven LOW. When the PCI_STOP input is
asserted, the PCI clock outputs (except the free-running PCI
clock) are driven LOW. When the PWR_DWN pin is asserted,
the reference oscillator and PLLs are shut down, and all out-
puts are driven LOW.
The CY2273A outputs are designed for low EMI emissions.
Controlled rise and fall times, unique output driver circuits and
factory-EPROM programmable output drive and slew-rate en-
able optimal configurations for EMI control.
CY2273A Selector Guide
CPU (60, 66.6, 75,
CPU (60, 66.6 MHz)
PCI (30, 33.3MHz)
AGP (60 or 66MHz)
1. One free-running PCI clock.
The CY2273A is a clock synthesizer/driver for a Pentium, Pen-
tium II, Cyrix, or AMD processor-based PC using Intel’s
82430TX, 82440LX, ALI Aladdin IV or Aladdin IV+ chipsets.
The CY2273A-1 outputs four CPU clocks at 2.5V or 3.3V with
up to 83.3MHz operation. There are seven PCI clocks, running
at 30 and 33.3MHz. One of the PCI clocks is free-running.
Additionally, the part outputs up to twelve 3.3V SDRAM clocks,
one 3.3V USB clock at 48 MHz, and one 3.3V reference clock
at 14.318 MHz. The CY2273A-2 is similar, except that
PCICLK4 and PCICLK5 are now AGP clocks. The CY2273A-3
is more suited to Pentium II systems, as it outputs one 2.5V
IOAPIC clock. Finally, the CY2273A-4 is similar to the
CY2273A-1 except that is supports 0-ns CPU-PCI delay.
1–5.5 ns 1–5.5 ns
Logic Block Diagram
REF0 (14.318 MHz)
Delay (-1,-2 option)
/1 or /1.25
/1 or /2
PCI [0-5], PCI [0-3]
USBCLK (48 MHz)
Intel and Pentium are registered trademarks of Intel Corporation. I
C is a trademark of Philips Corporation.
Cypress Semiconductor Corporation
3901 North First Street
October 12, 1998