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Home > Products > Integrated Circuits (ICs) > Clock/Timing > Clock Generators, PLLs, Frequency Synthesizers

NXP Semiconductors MC88915FN55R2

Name: MC88915FN55R2
Brand: NXP Semiconductors
SKU: MC88915FN55R2
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: MC88915FN55R2

Manufacturer:: NXP Semiconductors

Category:: Clock Generators, PLLs, Frequency Synthesizers

Package:: 28-LCC (J-Lead)

Datasheet:: MC88915FN55R2.pdf

Description:: IC CLOCK DRIVER 28PLCC

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Product details

Overview

MC88915FN55R2 from Motorola is a phase-locked loop (PLL) clock driver IC designed for high-performance PC and workstation clock distribution. It delivers five low-skew Q outputs (Q0–Q4) with <500 ps rising-edge skew, a 180°-phase-inverted Q5 output, a 2× frequency 2X_Q output (55 MHz max), and a Q/2 output - all locked to a single SYNC input. It supports input/output frequency ratios of 2:1, 1:1, and 1:2, enabling local frequency multiplication and synchronous multi-board clocking in CPU/memory subsystems.

For engineers reviewing the MC88915FN55R2 datasheet, MC88915FN55R2 pinout, MC88915FN55R2 application, or MC88915FN55R2 equivalent, this page provides verified technical context, exact pin functions, real-world timing roles in multiprocessor systems, and validated alternative options for PLL-based clock distribution designs requiring sub-nanosecond skew control and 55 MHz 2X_Q operation.

Technical Context

The MC88915FN55R2 implements a charge-pump PLL with voltage-controlled oscillator (VCO) optimized for 20–55 MHz operation. Its feedback path includes programmable divide-by-1/divide-by-2 selection via FREQ_SEL, enabling VCO frequency stabilization across input ranges from 2.5 MHz (with ÷2) to 20 MHz (with ÷1). The PLL locks rising edges of selected feedback outputs (e.g., Q/2, Q4, or 2X_Q) to SYNC inputs, establishing deterministic phase alignment.

It features dual SYNC inputs (SYNC[0], SYNC[1]) with REF_SEL selection, asynchronous RST (active-low), PLL_EN test-mode disable, and LOCK status output. All outputs drive ±36 mA at CMOS/TTL levels; inputs are TTL-compatible. Analog isolation via RC1 pin and external loop filter (470 kΩ + 0.1 µF) ensures jitter-free operation under digital supply noise.

Key Specifications

Parameter	Value and Actual Design Meaning
2X_Q Max Frequency	55 MHz - defines maximum system clock rate achievable via on-chip frequency doubling.
Q0–Q4 Max Frequency	27.5 MHz - sets upper limit for primary synchronized clock outputs in locked mode.
Output-to-Output Skew (Q0–Q4 rising)	<500 ps - guarantees tight timing alignment across five parallel clock domains on one board.
VCO Operating Range	20–55 MHz - constrains valid feedback configurations to maintain PLL stability and jitter performance.
Input Frequency Range (FREQ_SEL = HIGH)	5–13.75 MHz (for Q/2 feedback) to 20–55 MHz (for 2X_Q feedback) - determines viable reference clock sources without external dividers.
Drive Strength	±36 mA per output - enables direct fanout to ≥10 CMOS loads or ≥5 TTL loads without buffers.
LOCK Output Function	Open-drain indicator (12 mA sink only) - signals steady-state phase lock; not for active circuit control.

Pinout & Package

MC88915FN55R2 is housed in a 28-lead plastic leaded chip carrier (PLCC), case 776–02, with dimensions 12.32 × 12.32 × 0.81 mm (0.485″ × 0.485″ × 0.032″). Pin 1 is located at corner with index notch; top view orientation follows standard PLCC numbering (counterclockwise from index).

Pin/Terminal	Circuit Role	Design Meaning
SYNC[0], SYNC[1]	Dual reference clock inputs	Selectable via REF_SEL; allow redundancy or test-clock injection without hardware change.
REF_SEL	Reference source selector	Chooses between SYNC[0] and SYNC[1]; critical for board-level test flexibility and fault-tolerant clocking.
FREQ_SEL	Feedback divider control	Configures internal ÷1 (HIGH) or ÷2 (LOW) in PLL feedback path to keep VCO in optimal 20+ MHz range.
FEEDBACK	PLL phase detector input	Accepts selected output (Q/2, Q4, 2X_Q, etc.) to close control loop; determines final input/output ratio.
RC1	Analog reference current input	Connects to 470 kΩ resistor (to VCC or GND) to set charge-pump bias; prevents dead-band jitter.
Q0–Q4	Main synchronized clock outputs	Five identical, phase-aligned outputs with <500 ps mutual skew; drive CPU, cache, and bus logic.
Q5	Inverted clock output	180° phase-shifted version of Q0–Q4; used for complementary timing in latch-based interfaces.
2X_Q	Doubled-frequency output	Runs at exactly 2× Q-output frequency; feeds high-speed peripherals or memory controllers needing 2× base rate.
Q/2	Halved-frequency output	Runs at exactly 0.5× Q-output frequency; supplies lower-speed subsystems like I/O bridges or UARTs.
LOCK	Phase-lock status indicator	Active-high open-drain signal; valid only for passive monitoring - not for gating or reset assertion.
RST	Asynchronous reset input	Active-low; forces all outputs low immediately, overriding PLL state - essential for power-up synchronization.
PLL_EN	PLL enable/disable control	Pulling LOW disables VCO and enters static test mode; allows board-level validation with sub-MHz clocks.
VCC, GND	Power and ground terminals	Eight dedicated pins (including quiet analog VCC/GND) minimize supply noise coupling into PLL core.

Key Features

Feature	Design Value
Five Q outputs with <500 ps rising-edge skew	Enables simultaneous clocking of multiple high-speed ASICs or CPUs on a single PCB without trace-length matching.
Programmable feedback division (÷1/÷2)	Allows use of low-frequency crystal references (e.g., 10 MHz) while maintaining VCO in low-jitter 20–55 MHz range.
Dual SYNC inputs with REF_SEL	Supports hot-swappable clock sources or seamless transition from main to backup reference during runtime.
Test mode (PLL_EN = LOW)	Permits full functional testing at arbitrary low frequencies (e.g., 100 kHz), bypassing PLL lock requirements.
±36 mA CMOS/TTL output drive	Eliminates need for external buffer ICs when driving moderate fanout (≤10 loads), reducing BOM count and layout area.

Applications

High-Performance Workstation CPU Clocking	Multi-Board Synchronous Memory Subsystem
Use Scenario: Distributing a centralized 25 MHz system clock to CPU, FPU, and cache controller on a single motherboard with sub-nanosecond timing tolerance. IC Role / Device Role / Timing Role: MC88915FN55R2 acts as a zero-delay, low-skew clock repeater with 2× multiplication capability - generating 50 MHz 2X_Q for CPU core and 25 MHz Q outputs for cache tags and ALU pipelines. Use Value: Achieves <500 ps inter-output skew across five Q outputs, eliminating setup/hold violations in 33–50 MHz synchronous buses without manual trace tuning.	Use Scenario: Synchronizing clock domains across three separate memory cards (DRAM, SRAM, FIFO) connected to a central CMMU in a multiprocessing server chassis. IC Role / Device Role / Timing Role: MC88915FN55R2 serves as a board-level PLL node, locking to a backplane-distributed 12.5 MHz SYNC signal and regenerating local 25 MHz Q outputs and 50 MHz 2X_Q for memory controllers. Use Value: Enables <1.2 ns worst-case part-to-part skew between boards using common SYNC, ensuring deterministic read/write strobe alignment across distributed memory banks.
Legacy x86 System Clock Synthesis	Industrial Control Backplane Timing
Use Scenario: Replacing discrete crystal oscillators and logic dividers in an embedded 486-based industrial controller requiring 33 MHz CPU clock and 16.5 MHz peripheral clock. IC Role / Device Role / Timing Role: MC88915FN55R2 functions as a programmable clock synthesizer - accepting 16.5 MHz crystal input and generating 33 MHz 2X_Q (for CPU) and 16.5 MHz Q outputs (for ISA bus logic) via Q/2 feedback. Use Value: Reduces component count by 4–6 parts (oscillator + dividers + buffers) while improving long-term frequency stability and temperature drift vs. RC-based solutions.	Use Scenario: Providing deterministic clock distribution in a ruggedized PLC backplane where EMI and supply noise threaten timing integrity across I/O modules. IC Role / Device Role / Timing Role: MC88915FN55R2 operates as a noise-immune clock conditioner - using analog-isolated RC1 filtering and quiet VCC/GND pins to suppress >100 mV supply transients from affecting output phase. Use Value: Limits phase deviation to ≤100 ps under 100 mV VCC step disturbance, preventing metastability in time-critical digital I/O sampling circuits.

High-Performance Workstation CPU Clocking

Multi-Board Synchronous Memory Subsystem

Use Scenario: Distributing a centralized 25 MHz system clock to CPU, FPU, and cache controller on a single motherboard with sub-nanosecond timing tolerance.

IC Role / Device Role / Timing Role: MC88915FN55R2 acts as a zero-delay, low-skew clock repeater with 2× multiplication capability - generating 50 MHz 2X_Q for CPU core and 25 MHz Q outputs for cache tags and ALU pipelines.

Use Value: Achieves <500 ps inter-output skew across five Q outputs, eliminating setup/hold violations in 33–50 MHz synchronous buses without manual trace tuning.

Use Scenario: Synchronizing clock domains across three separate memory cards (DRAM, SRAM, FIFO) connected to a central CMMU in a multiprocessing server chassis.

IC Role / Device Role / Timing Role: MC88915FN55R2 serves as a board-level PLL node, locking to a backplane-distributed 12.5 MHz SYNC signal and regenerating local 25 MHz Q outputs and 50 MHz 2X_Q for memory controllers.

Use Value: Enables <1.2 ns worst-case part-to-part skew between boards using common SYNC, ensuring deterministic read/write strobe alignment across distributed memory banks.

Legacy x86 System Clock Synthesis

Industrial Control Backplane Timing

Use Scenario: Replacing discrete crystal oscillators and logic dividers in an embedded 486-based industrial controller requiring 33 MHz CPU clock and 16.5 MHz peripheral clock.

IC Role / Device Role / Timing Role: MC88915FN55R2 functions as a programmable clock synthesizer - accepting 16.5 MHz crystal input and generating 33 MHz 2X_Q (for CPU) and 16.5 MHz Q outputs (for ISA bus logic) via Q/2 feedback.

Use Value: Reduces component count by 4–6 parts (oscillator + dividers + buffers) while improving long-term frequency stability and temperature drift vs. RC-based solutions.

Use Scenario: Providing deterministic clock distribution in a ruggedized PLC backplane where EMI and supply noise threaten timing integrity across I/O modules.

IC Role / Device Role / Timing Role: MC88915FN55R2 operates as a noise-immune clock conditioner - using analog-isolated RC1 filtering and quiet VCC/GND pins to suppress >100 mV supply transients from affecting output phase.

Use Value: Limits phase deviation to ≤100 ps under 100 mV VCC step disturbance, preventing metastability in time-critical digital I/O sampling circuits.

Equivalent & Alternatives

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

Alternative Part	Technical Difference	Application Difference	Selection Advice
MC88915FN70	Higher 2X_Q max frequency (70 MHz vs. 55 MHz); otherwise identical pinout, architecture, and feature set.	Suitable for systems requiring >55 MHz doubled output (e.g., 68060-based workstations), but consumes more power at same load.	Select MC88915FN70 only if design requires guaranteed 2X_Q operation above 55 MHz; otherwise MC88915FN55R2 offers better power efficiency at 27.5 MHz Q outputs.
ICS552-01LFT	Single 3.3 V supply, integrated loop filter, no FREQ_SEL or dual SYNC; 50 MHz max 2X output; different pinout and register interface.	Targets modern low-voltage designs with simplified layout; lacks test-mode flexibility and analog isolation controls of MC88915FN55R2.	Choose ICS552-01LFT for new 3.3 V designs prioritizing integration and footprint reduction; retain MC88915FN55R2 for legacy 5 V systems, rigorous skew control, or production testability.

Compared with MC88915FN70 and ICS552-01LFT, the MC88915FN55R2 uniquely balances 5 V compatibility, configurable feedback division, dual-SYNC redundancy, and proven sub-500 ps skew in high-noise computing environments - making it irreplaceable in field-deployed 5 V workstation and industrial control clock trees.

Availability

MC88915FN55R2 is available at Aetrix Electronics and suitable for high-performance workstation CPU clocking, multi-board memory synchronization, legacy x86 system synthesis, and industrial control backplane timing requiring stable component supply and long-lifecycle support.

Supply support for MC88915FN55R2 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 (now part of NXP Semiconductors) was a pioneering semiconductor manufacturer known for high-reliability timing, microcontroller, and analog products serving computing and industrial markets.

The MC88915FN55R2 belongs to Motorola's TIMING SOLUTIONS product line, engineered specifically for low-skew, multi-output clock distribution in high-speed computing systems where deterministic phase alignment and board-level testability are critical.

FAQ

What is the maximum guaranteed operating frequency of the 2X_Q output for MC88915FN55R2?

The MC88915FN55R2 guarantees a maximum 2X_Q output frequency of 55 MHz under phase-locked conditions with 50 pF load. This rating is strictly limited to operation within the device's specified VCO range (20–55 MHz) and requires proper external loop filter configuration (470 kΩ + 0.1 µF) and analog supply decoupling per Figure 6 of the datasheet. Exceeding 55 MHz risks loss of lock or increased jitter.

How does the FREQ_SEL pin affect the input frequency range supported by MC88915FN55R2?

The FREQ_SEL pin selects between ÷1 and ÷2 division in the PLL feedback path. When HIGH, the VCO runs at the same frequency as the desired Q outputs, allowing SYNC inputs as low as 5 MHz (with Q/2 feedback). When LOW, the VCO runs at twice the Q-output frequency, enabling valid SYNC inputs down to 2.5 MHz - essential for using low-cost, low-frequency crystals while keeping the VCO in its optimal 20+ MHz low-jitter range.

Can the LOCK output of MC88915FN55R2 be used to control downstream logic or reset circuits?

No. The LOCK output of MC88915FN55R2 is explicitly intended only for passive monitoring or evaluation purposes. The datasheet warns that LOCK may remain low even when phase-locked under certain conditions, and specifies it must not drive any active circuitry. Its 12 mA sink capability is insufficient for logic-level signaling, and its timing behavior is not guaranteed for control-plane use - always verify lock status via oscilloscope or logic analyzer, not automated circuit response.

What is the purpose of the RC1 pin on MC88915FN55R2, and what resistor value should be used?

The RC1 pin connects to an external reference resistor that injects controlled current into the PLL's charge pump, eliminating dead-band-induced jitter. For VCO operation above 40 MHz (i.e., 2X_Q ≥ 55 MHz), a 470 kΩ resistor tied to analog VCC or GND is required. If the VCO runs below 40 MHz, a 1 MΩ resistor must be substituted - using 470 kΩ in low-frequency configurations causes excessive charge-pump current and unstable lock behavior.

Does MC88915FN55R2 support operation with non-50% duty-cycle input clocks?

Yes. The MC88915FN55R2 aligns rising edges of the FEEDBACK and SYNC inputs, so the SYNC input does not require a 50% duty cycle. This is confirmed in Timing Note on page 8: "The MC88915 aligns rising edges of the FEEDBACK input and SYNC input, therefore the SYNC input does not require a 50% duty cycle." This simplifies clock source selection and eliminates need for external duty-cycle correction circuits.

MC88915FN55R2 Specifications

Product attributes: Attribute value

Manufacturer:: NXP Semiconductors

Series:: -

Package/Case:: 28-LCC (J-Lead)

Packaging:: Tape & Reel (TR)

Product Status:: Obsolete

Programmable:: Not Verified

Type:: Clock Driver, Fanout Distribution, Multiplexer

PLL:: Yes

Input:: TTL

Output:: CMOS, TTL

Number of Circuits:: 1

Ratio - Input:Output:: 3:8

Differential - Input:Output:: No/No

Frequency - Max:: 55MHz

Divider/Multiplier:: Yes/Yes

Voltage - Supply:: 4.75V ~ 5.25V

Operating Temperature:: 0°C ~ 70°C

Mounting Type:: Surface Mount

Grade:: -

Qualification:: -

Supplier Device Package:: 28-PLCC (11.51x11.51)

MC88915FN55R2 FAQ

1.How can I place an order for MC88915FN55R2 through Aetrix?

Please submit a Request for Quotation (RFQ) for MC88915FN55R2 on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.

2.Are the price and stock information for MC88915FN55R2 reliable?

The price and inventory of MC88915FN55R2 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for MC88915FN55R2 is usually 5 days.

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MC88915FN55R2 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your MC88915FN55R2 order is processed, you will receive an email with the shipment details and tracking number.

Note: Tracking information may take up to 24 hours to appear. Express delivery typically takes 3–5 business days.

5.How can I obtain technical support or documentation for MC88915FN55R2?

For technical support, including MC88915FN55R2 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your MC88915FN55R2 requirements.

6.How does Aetrix verify that MC88915FN55R2 is sourced from the original manufacturer or authorized distributors?

All MC88915FN55R2 products on Aetrix are procured from qualified distributors and authorized channels. Our dedicated quality assurance team conducts strict verification, including traceability checks and, if necessary, third-party testing. This ensures that MC88915FN55R2 meets industry standards.

7.What is the process for return or replacement of MC88915FN55R2?

All MC88915FN55R2 units undergo pre-shipment inspection (PSI). If there is an issue with MC88915FN55R2, returns or replacements are accepted under the following conditions:

1.Quantity discrepancies, incorrect items, or visible external defects (such as breakage or corrosion), acknowledged by Aetrix.

2.The issue is reported within 90 days of delivery.

3.The MC88915FN55R2 part is unused and in its original packaging.

Return procedure for MC88915FN55R2:

1.Submit a request within 90 days.

2.Obtain a Return Material Authorization (RMA) from Aetrix.

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