MC88915FN55

Clock Generators, PLLs, Frequency Synthesizers Overview

The MC88915FN55 is a PLL-based clock driver designed for high-performance PC and workstation applications. It locks low-skew outputs to an input reference clock, providing zero-delay distribution or frequency multiplication (2X). The device features five Q outputs (Q0–Q4) with less than 500 ps skew, an inverted Q5 output, a 2X_Q output running at twice the Q frequency, and a Q/2 output. It operates within a supply voltage range of 4.75V to 5.25V. The maximum operating frequency for the 2X_Q output is 55 MHz, while the Q outputs are limited to 27.5 MHz.

Clock Generators, PLLs, Frequency Synthesizers Feature Summary

• Phase-locked loop technology ensures frequency and phase locking with less than 500 ps output-to-output skew between rising edges of Q0-Q4.
• Provides multiple frequency ratios (1:2, 1:1, 2:1) via selectable feedback configurations and FREQ_SEL pin.
• Outputs deliver ±36 mA drive current, compatible with both CMOS and TTL logic levels.
• Includes a test mode (PLL_EN low) for low-frequency board-level testing without PLL lock requirements.

Clock Generators, PLLs, Frequency Synthesizers Applications

• Clock distribution for high-performance personal computers and workstations.
• Synchronous multi-board systems requiring central system clock distribution.
• Applications requiring frequency multiplication from low-frequency references.

Clock Generators, PLLs, Frequency Synthesizers Procurement Notes

Verify the manufacturer origin, as this component was originally produced by Motorola and later acquired by NXP USA Inc. Confirm the specific suffix 'FN' corresponds to the 28-pin PLCC package (Case 776-02). Ensure the FN55 variant matches the required 55 MHz maximum frequency specification for the 2X_Q output.

Clock Generators, PLLs, Frequency Synthesizers Selection Notes

Select the MC88915FN55 when the application requires a maximum 2X_Q frequency of 55 MHz. If higher frequencies up to 70 MHz are needed, consider the MC88915FN70 variant. Ensure the design accommodates the 5.0V ±5% power supply requirement and provides adequate bypass capacitance (0.1μF and 10μF) near the analog pins to minimize jitter.

Clock Generators, PLLs, Frequency Synthesizers Part Context

The MC88915 belongs to the Motorola/NXP 88915 series of timing solutions. It is part of a family that includes variants like the MC88915FN70. The device utilizes Yield Surface Modeling (YSM) for performance guaranteeing. It is distinct from general-purpose logic drivers due to its integrated VCO and charge pump loop filter interface.

Clock Generators, PLLs, Frequency Synthesizers Replacement Considerations

Public confirmed substitute part numbers include MC88915FN70 for higher frequency requirements. Other manufacturers such as IDT and NXP list similar PLL clock drivers in the 88915 series, but direct functional equivalence must be verified against the specific electrical characteristics and pinout compatibility.

Clock Generators, PLLs, Frequency Synthesizers FAQ

What is the function of the RC1 pin?

The RC1 pin is used for the external loop filter network. A 470kΩ resistor tied to Analog VCC or Analog GND is required to prevent jitter and inject current into the internal charge pump.

How does the FREQ_SEL pin affect operation?

The FREQ_SEL pin selects between divide-by-1 and divide-by-2 in the PLL feedback path. Holding it high (÷1) is standard; holding it low (÷2) allows the VCO to run optimally (>20 MHz) when using low-frequency reference inputs.

Can the LOCK output drive active circuitry?

No. The LOCK output should only be used for passive monitoring or evaluation. Under certain conditions, it may remain low even when phase-locked, making it unsuitable for driving active circuits.