Texas Instruments CDCEL925

Programmable 2-PLL VCXO Clock Synthesizer with 1.8-V LVCMOS Outputs

The CDCE925 and CDCEL925 are modular PLL-based low-cost, high-performance, programmable clock synthesizers, multipliers, and dividers. They generate up to five 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 two independent configurable PLLs. The CDCx925 has separate output supply pins, VDDOUT, which is 1.8 V for CDCEL925 and 2.5 V to 3.3 V for CDCE925. The input accepts an external crystal or LVCMOS clock signal. In case of a crystal input, an on-chip load capacitor is adequate for most applications. The value of the load capacitor is programmable from 0 pF to 20 pF. Additionally, an on-chip VCXO is selectable which allows synchronization of the output frequency to an external control signal, i.e., 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 27-MHz reference input frequency, for example. All PLLs supports SSC (spread-spectrum clocking). SSC can be center-spread or down-spread clocking which 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 optimized jitter transfer characteristic of each PLL. The device supports nonvolatile EEPROM programming for easy customization of the device in the application. It is preset to a factory default configuration and can be re-programmed to a different application configuration before it goes onto the PCB or re-programmed by in-system programming. All device settings are programmable through SDA/SCL bus, a 2-wire serial interface. Three, free programmable control inputs, S0, S1, and S2, can be used to select different frequencies, or change SSC setting for lowering EMI, or other control features like outputs disable to low, outputs 3-state, power down, PLL bypass, etc.). The CDCx925 operates in a 1.8-V environment. It is characterized for operation from -40C to 85C