cy2547/CY2545 pdf datasheet (Q

cy2547/CY2545 Quad PLL Programmable Spread Spectrum? Clock Generator with Serial I2C Interface

The CY2545 and CY2547 have four I2C programmable PLLs
available to generate output frequencies ranging from 3 to 166
MHz. The advantage of having four PLLs is that a single device
generates up to four independent frequencies from a single
crystal. Two sets of frequencies for each PLL can be
programmed. This enables in system frequency switching using
multifunction frequency select pin, FS.
I2C Programming
The CY2545 and CY2547 have a serial I2C interface that
programs the configuration memory array to synthesize output
frequencies by programmable output divider, spread characteristics,
drive strength, and crystal load capacitance. I2C can also
be used for in system control of these programmable features.
Input Reference Clocks
The input to the CY2545 and CY2547 is either a crystal or a clock
signal. The input frequency range for crystals is 8 MHz to 48
MHz. There is provision for two reference clock inputs, CLKIN
and EXCLKIN with frequency range of 8 MHz to 166 MHz. For
both devices, when CLKIN signal at pin 21 is used as a reference
input, a valid signal at EXCLKIN (as specified in the AC and DC
Electrical Specification table), must be present for the devices to
operate properly.
Multiple Power Supplies
The CY2545 and CY2547 are designed to operate at internal
core supply voltage of 1.8V. In the case of the high voltage part
(CY2545), an internal regulator is used to generate 1.8V from the
2.5V/3.0V/3.3V VDD supply voltage at pin 22. For the low voltage
part (CY2547), this internal regulator is bypassed and 1.8V at
VDD pin 22 is directly used.