NXP Semiconductors MC88915TFN55

Overview

MC88915TFN55 from Motorola is a 55 MHz, 5 V, low-skew PLL clock driver in 28-lead PLCC package, delivering five phase-locked Q outputs (Q0–Q4) with <500 ps rising-edge skew, one inverted Q5 output, plus 2X_Q and Q/2 outputs - designed for synchronous clock distribution in high-performance PC and workstation motherboards.

For engineers reviewing the MC88915TFN55 datasheet, MC88915TFN55 pinout, MC88915TFN55 application, or MC88915TFN55 equivalent, key selection criteria include guaranteed 55 MHz 2X_Q max frequency, ±36 mA CMOS/TTL-compatible drive strength, FREQ_SEL programmable feedback divide ratio, OE/RST 3-state control, and LOCK indicator for phase-lock status verification.

Technical Context

The MC88915TFN55 implements a voltage-controlled oscillator (VCO) locked to a 5–27.5 MHz SYNC input via internal PLL, supporting 1:2, 1:1, and 2:1 input/output frequency ratios. Its feedback path includes FREQ_SEL-selectable ÷1 or ÷2 division before the clock distribution network, enabling optimal VCO operation ≥20 MHz even with low-frequency references.

It features dual SYNC inputs (SYNC0/SYNC1), test-mode support via PLL_EN, and synchronized multi-board clock distribution using shared reference clocks. All outputs - including 2X_Q (110 MHz), Q0–Q4 (27.5 MHz), Q5 (inverted), and Q/2 (13.75 MHz) - are driven with matched ±36 mA current into 50 Ω loads terminated at VCC/2.

Key Specifications

Pinout & Package

MC88915TFN55 is housed in a 28-lead plastic leaded chip carrier (PLCC), case 776–02, with gull-wing leads and exposed thermal pad not electrically connected. Pin numbering follows top-view convention per Motorola datasheet Figure 1.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar PLL clock driver applications.

Compared with MC88915TFN70 and ICS552GI-01LFT, the MC88915TFN55 delivers optimal jitter performance and skew control at 5 V for legacy high-speed computing platforms, while offering unique test-mode flexibility and analog/digital supply isolation absent in newer low-voltage alternatives.

Availability

MC88915TFN55 is available at Aetrix Electronics and suitable for PC motherboard design, industrial backplane timing, and legacy microprocessor system clocking requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for MC88915TFN55 includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Motorola Semiconductor (now part of NXP Semiconductors) pioneered high-performance clock distribution ICs for computing infrastructure, emphasizing low skew, jitter resilience, and robust industrial qualification.

The MC88915T family was engineered specifically for synchronous clock fanout in 5 V PC and workstation architectures, addressing stringent skew, drive strength, and multi-board phase alignment requirements of mid-1990s high-end computing platforms.

FAQ

What is the maximum guaranteed frequency for the 2X_Q output of the MC88915TFN55?

The MC88915TFN55 guarantees a maximum 2X_Q output frequency of 55 MHz under phase-locked conditions with all outputs loaded into 50 Ω terminations at VCC/2. This corresponds to a 27.5 MHz Q-output domain and is validated across –40°C to +85°C operating temperature.

How does the FREQ_SEL pin affect the MC88915TFN55's PLL operation?

The FREQ_SEL pin selects the feedback divider ratio in the MC88915TFN55's PLL: high = ÷1, low = ÷2. When held high, the VCO runs at the same frequency as the 2X_Q output; when low, it runs at half that rate - enabling stable VCO operation ≥20 MHz even with low-frequency SYNC inputs like 5–13.75 MHz.

Can the MC88915TFN55 drive 50 Ω transmission lines directly without external buffers?

Yes, the MC88915TFN55 delivers ±36 mA output drive strength into 50 Ω loads terminated at VCC/2, meeting Motorola's specified rise/fall times (<2.5 ns) and pulse width accuracy. This eliminates the need for external buffers in point-to-point motherboard clock trees, reducing component count and jitter sources.

What is the function of the OE/RST pin on the MC88915TFN55?

The OE/RST pin on the MC88915TFN55 controls output state: pulling it low places 2X_Q, Q0–Q4, Q5, and Q/2 into high-impedance mode for board test or hot-swap isolation; releasing it high resets Q0–Q4 and Q5 to low state, while 2X_Q assumes the inverse of the selected SYNC input - enabling deterministic startup sequencing.

Does the MC88915TFN55 support dual clock inputs, and how are they used?

Yes, the MC88915TFN55 provides two TTL-compatible SYNC inputs (SYNC0 and SYNC1). SYNC0 serves as the primary reference; SYNC1 enables redundancy in fault-tolerant systems or acts as a dedicated test clock input during low-frequency board validation - both are internally OR'd and selectable via external logic.