(1pc) MPC974FA Motorola, PLL based clock generator

The MPC974 is a fully integrated PLL based clock generator and clock distribution chip which operates from a 3.3V supply. The MPC974 is ideally suited for high speed, timing critical designs which need a high level of clock fanout. The device features 15 high drive LVCMOS outputs, each output has the capability of driving a 50Ω parallel terminated transmission line or two 50Ω series terminated transmission lines on the incident edge. 

• Fully Integrated PLL 

• Two Reference Clock Inputs for Redundant Clock Applications 

• High Impedance Output Control 

• Logic Enable on the Outputs 

• 3.3V VCC Supply 

• Output Frequency Configurable 

• LQFP Packaging 

• ±100ps Typical Cycle–to–Cycle Jitter 

The MPC974 features 3 independent frequency programmable banks of outputs. The frequency programmability offers the capability of establishing output frequency relationships of 1:1, 2:1, 3:1, 3:2 and 3:2:1. In addition, the device features a separate feedback output which allows for a wide variety of input/output frequency multiplication alternatives. The VCO_Sel pin provides an extended VCO lock range for added flexibility and general purpose usage. The TCLK0 and TCLK1 inputs provide a method for dynamically switching the PLL between two different clock sources. The PLL has been optimized to provide small deviations in output pulse width and well controlled, slow transition back to lock when the inputs are switched between two references that are equal in frequency but out of phase with each other. This feature makes the MPC974 a solution for fault tolerant applications which require redundant clock sources. For designs in which fault tolerance is critical, other products may provide more control over the clock switch functions. For these features please refer to the MPC993 datasheet. All of the control pins are LVTTL/LVCMOS level inputs. The Fsel pins control the VCO divide ratios that are applied to the various output banks and the feedback output. The MR input will reset the internal flip flops and place the outputs in high impedance when driven LOW. The OE pin will force all of the outputs except the feedback output LOW to allow for acquiring phase lock prior to providing clocks to the rest of the system. Note that the OE pin is not synchronized to the internal clock. As a result, the initial pulse after de–assertion of the OE pin may be distorted. The PLL_En pin allows the PLL to be bypassed for board level functional test. When bypassed the signal on the selected TCLK will be routed around the PLL and will drive the internal dividers directly.

The MPC974 is packaged in the 52–lead LQFP package to provide optimum electrical performance as well as minimize board space requirements. The device is specified for 3.3V VCC.