MOTOROLA

SEMICONDUCTOR TECHNICAL DATA

1

REV 2

1/97

Not Recommended for New Designs

See MPC972 or MPC974

Low Voltage PLL Clock Driver

The MPC970 is a 3.3V compatible, PLL based clock driver devices

targeted for high performance RISC or CISC processor based systems.

The MPC970 was designed specifically to drive today’s PowerPC 601

and Pentium processors while providing the necessary performance to

address higher frequency PowerPC 601 as well as PowerPC 603 and

PowerPC 604 applications. The 2x_PCLK output can toggle at up to

250MHz while the remaining outputs can be configured to drive the other

system clocks for MPC 601 based systems. As the processor based

clock speeds increase the processor bus will likely run at one third or

even one fourth the processor clock. The MPC970 supports the

necessary waveforms to drive the BCLKEN input signal of the MPC 601

when the processor bus is running at a lower frequency than the

processor. The MPC970 uses an advanced PLL design which minimizes

the jitter generated on the outputs. The jitter specification is well within the

requirements of the Pentium processor and meets the stringent

preliminary specifications of the PowerPC 603 and PowerPC 604

processors. The application section of this data sheet deals in more detail

with driving PowerPC and Pentium processor based systems.

The external feedback option of the MPC970 provides for a near zero delay between the reference clock input and the outputs

of the device. This feature is required in applications where a master clock is being picked up off the backplane and regenerated

and distributed on a daughter card. The advanced PLL of the MPC970 eliminates the dead zone of the phase detector and

minimizes the jitter of the PLL so that the phase error variation is held to a minimum. This phase error uncertainty makes up a

major portion of the part–to–part skew of the device.

For single clock driver applications the MPC970 provides an internal oscillator and internal feedback to simplify board layout

and minimize system cost. By using the on–board crystal oscillator the MPC970 acts as both the clock generator and distribution

chip. The external component is a relatively inexpensive crystal rather than a more expensive oscillator. Since in single board

applications the delay between the input reference and the outputs is inconsequential an internal feedback option is offered. The

internal feedback simplifies board design in that the system designer need not worry about noise being coupled into the feedback

line due to board parasitics and layout. The internal feedback is a fixed divide by 32 of the VCO. This divide ratio ensures that the

input crystals will be

≤20MHz, thus keeping the crystal costs down and ensuring availability from multiple vendors.

PowerPC is a trademark of International Business Machines Corporation. Pentium is a trademark of Intel Corporation.

MPC970

LOW VOLTAGE

PLL CLOCK DRIVER

FA SUFFIX

52–LEAD TQFP PACKAGE

CASE 848D–03