Programmable 4-PLL VCXO clock synthesizer with 2.5-V or 3.3-V LVCMOS outputs

The CDCE949 and CDCEL949 are modular PLL-based low cost, high-performance, programmable clock synthesizers, multipliers, and dividers. These devices generate up to nine output clocks from a single input frequency. Each output is programmable in-system for any clock frequency up to 230MHz, using up to four independent configurable PLLs.

The CDCEx949 has separate output supply pins (VDDOUT): 1.8V for the CDCEL949 and 2.5V to 3.3V for the 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 0pF to 20pF. Additionally, an on-chip VCXO is selectable, allowing synchronization of the output frequency to an external control signal, that is, a PWM signal.

The deep M/N divider ratio allows the generation of 0ppm audio or video, networking (WLAN, Bluetooth, Ethernet, GPS) or Interface (USB, IEEE1394, Memory Stick) clocks from a reference input frequency, such as 27MHz.

All PLLs support spread spectrum clocking (SSC). SSC can be center-spread or down-spread clocking. This is a common technique to reduce electromagnetic 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. The CDCEx949 is preset to a factory-default configuration. The device 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 and SCL bus, a 2-wire serial interface.