Texas Instruments CDCE949

Programmable 4-PLL VCXO Clock Synthesizer with 1.8V, 2.5V and 3.3V LVCMOS Outputs

The CDCE949 and CDCEL949 are modular PLL-based low cost, high-performance, programmable clock synthesizers, multipliers and dividers. They generate up to 9 output clocks from a single input frequency. Each output can be programmed in-system for any clock frequency up to 230 MHz, using up to four independent configurable PLLs. The CDCx949 has separate output supply pins, VDDOUT, 1.8 V for the CDCEL949, and 2.5 V to 3.3 V for CDCE949. The input accepts an external crystal or LVCMOS clock signal. If an external crystal is used, an on-chip load capacitor is adequate for most applications. The value of the load capacitor is programmable from 0 to 20 pF. Additionally, an on-chip VCXO is selectable, allowing synchronization of the output frequency to an external control signal, i.e. a PWM signal. The deep M/N divider ratio allows the generation of zero-ppm audio/video, networking (WLAN, BlueTooth™, Ethernet, GPS) or Interface (USB, IEEE1394, Memory Stick) clocks from a reference input frequency such as 27-MHz. All PLLs support SSC (Spread-Spectrum Clocking). SSC can be Center-Spread or Down-Spread clocking. This is a common technique to reduce electro-magnetic interference (EMI). Based on the PLL frequency and the divider settings, the internal loop-filter components are automatically adjusted to achieve high stability, and to optimize the jitter-transfer characteristics of each PLL. The device supports non-volatile EEPROM programming for easy customization of the device to the application. It is preset to a factory-default configuration. It can be reprogrammed to a different application configuration before PCB assembly, or reprogrammed by in-system programming. All device settings are programmable through the SDA/SCL bus, a 2-wire serial interface. Three programmable control inputs, S0, S1 and S2, can be used to control various aspects of operation including frequency selection, changing the SSC parameters to lower EMI, PLL bypass, power down, and choosing between low level or 3-state for the output-disable function. The CDCx949 operates in a 1.8-V environment. It is characterized for operation from -40C to 85C.