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NXP Semiconductors MC88915FN55
- Part No.:
- MC88915FN55
- Manufacturer:
- NXP Semiconductors
- Package:
- 28-LCC (J-Lead)
- Datasheet:
-
MC88915FN55.pdf
- Description:
- IC CLOCK DRIVER 28PLCC
- Quantity:
- Payment:
- Shipping:
Inventory:1,585
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Product details
Overview
MC88915FN55 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. Its FREQ_SEL pin enables programmable feedback division (÷1 or ÷2), supporting input frequencies from 5 MHz to 27.5 MHz while maintaining VCO operation ≥20 MHz.
For engineers reviewing the MC88915FN55 datasheet, MC88915FN55 pinout, MC88915FN55 application, or MC88915FN55 equivalent, key selection criteria include guaranteed 55 MHz 2X_Q output frequency, 500 ps Q-output skew, dual SYNC inputs with REF_SEL selection, PLL_EN test-mode support, and PLCC-28 package compatibility with legacy Motorola timing designs.
Technical Context
The MC88915FN55 implements a charge-pump PLL with voltage-controlled oscillator (VCO) optimized for 20–55 MHz operation. Its feedback path supports selectable division ratios (÷1 or ÷2 via FREQ_SEL), enabling three input-to-Q-output frequency relationships: 2:1, 1:1, and 1:2. The internal loop filter uses an external RC network on RC1 pin to stabilize phase alignment between SYNC and FEEDBACK inputs.
It features dual TTL-compatible SYNC inputs (SYNC[0], SYNC[1]), programmable reference selection (REF_SEL), asynchronous reset (RST), and lock detection (LOCK) - all operating at 5.0 V ±5%. Output drive strength is ±36 mA per Q output at CMOS levels, with dedicated analog supply pins (VCC(AN)/GND(AN)) isolated via on-board RC filtering per Figure 6.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| 2X_Q Max Frequency | 55 MHz - defines highest synchronous clock rate deliverable to CPU/memory subsystems |
| Q0–Q4 Max Frequency | 27.5 MHz - maximum system clock rate for main logic domains under PLL lock |
| Output-to-Output Skew (Q0–Q4) | <500 ps rising-edge - ensures timing-critical parallel bus interfaces meet setup/hold margins |
| VCO Operating Range | 20–55 MHz - constrains minimum input frequency when FREQ_SEL = LOW (÷2 mode) |
| Input Voltage Compatibility | TTL-level inputs (VIH ≥2.0 V, VIL ≤0.8 V) - interoperable with standard 5 V logic without level shifters |
| Output Drive Strength | ±36 mA per Q output - drives up to 10 TTL loads or 20 CMOS loads directly |
| Power Supply | 5.0 V ±5% - requires stable regulated rail; analog/digital VCC pins must be decoupled per Figure 6 |
Pinout & Package
MC88915FN55 is housed in a 28-lead plastic leaded chip carrier (PLCC), case 776–02, with dimensions 11.43 mm × 11.43 mm × 0.66–0.81 mm (R/U/H). Pin 1 is located at corner with index mark; leads are arranged in counter-clockwise order when viewed from top.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| SYNC[0], SYNC[1] | Dual reference clock inputs | Selectable primary clock source; REF_SEL chooses between them for PLL reference |
| FREQ_SEL | Feedback divider control | High = ÷1, Low = ÷2 - adjusts VCO frequency to maintain ≥20 MHz operation across input range |
| FEEDBACK | PLL phase detector input | Accepts selected Q or 2X_Q output to close PLL loop; determines final output frequency ratio |
| RC1 | External loop filter connection | Connects to 470 kΩ resistor and 0.1 µF capacitor - sets PLL bandwidth and jitter performance |
| Q0–Q4 | Main clock outputs | Five identical, phase-aligned outputs with <500 ps mutual skew - drive CPU, chipset, memory controllers |
| Q5 | Inverted clock output | 180° phase-shifted version of Q0–Q4 - used for differential clocking or latch timing |
| 2X_Q | Double-frequency output | Runs at twice Q-output frequency - supplies high-speed peripherals or internal VCO feedback |
| Q/2 | Half-frequency output | Runs at half Q-output frequency - provides lower-speed domain clocks without external dividers |
| LOCK | Phase-lock status indicator | Open-drain active-high signal - valid only for passive monitoring; not for control logic |
| RST | Asynchronous reset | Active-low signal resets all outputs immediately - used for power-on initialization or fault recovery |
| PLL_EN | PLL enable/disable | Low disables VCO and enters static test mode - allows board-level validation at sub-MHz frequencies |
| VCC, GND (x4 each) | Power and ground | Digital VCC/GND pins (pins 4,8,10,26); analog VCC(AN)/GND(AN) (pins 16,17) require separate bypassing |
Key Features
| Feature | Design Value |
|---|---|
| Five synchronized Q outputs | Q0–Q4 provide <500 ps rising-edge skew - eliminates inter-signal timing violations in multi-chip clock trees |
| Programmable feedback division | FREQ_SEL selects ÷1 or ÷2 in PLL feedback path - extends usable input frequency range down to 2.5 MHz |
| Dual SYNC inputs with REF_SEL | Enables redundant clock sources or system-level clock switching - improves reliability in multi-board systems |
| Test mode via PLL_EN | Pulling PLL_EN low disables VCO and enables divide-by-2/4/8 test outputs - simplifies low-frequency ATE validation |
| Analog/digital supply isolation | Dedicated VCC(AN)/GND(AN) pins with recommended RC filter - reduces digital noise coupling into PLL VCO |
| Lock detection with fail-safe use | LOCK output indicates steady-state phase lock but is not guaranteed during transient conditions - intended for debug only |
Applications
| Workstation CPU Clock Distribution | Multi-Board Synchronous Systems |
|---|---|
Use Scenario: Distributing a central 27.5 MHz system clock to CPU, cache controller, and I/O bridge on a high-end workstation motherboard. IC Role / Device Role / Timing Role: MC88915FN55 acts as the primary PLL-based clock fanout buffer, generating phase-aligned Q0–Q4 outputs with <500 ps skew to meet tight setup/hold windows. Use Value: Eliminates need for discrete delay-matching traces or external skew-compensation circuits, reducing layout complexity and improving timing margin predictability. |
Use Scenario: Synchronizing clock domains across multiple plug-in cards (CPU, memory, CMMU) in a backplane-based multiprocessing system. IC Role / Device Role / Timing Role: MC88915FN55 serves as a board-level clock multiplier and distributor, locking to a shared 12.5 MHz backplane SYNC and generating local 25 MHz Q outputs and 50 MHz 2X_Q signals. Use Value: Enables zero-delay, low-skew clock delivery across boards - critical for coherent cache protocols and deterministic inter-processor communication. |
| Legacy PC Chipset Timing | Industrial Control Backplane Clocking |
Use Scenario: Providing timing signals to Intel 486/Pentium-era chipsets requiring 25–33 MHz clocks with precise phase alignment between address, data, and control buses. IC Role / Device Role / Timing Role: MC88915FN55 functions as a programmable clock synthesizer, using FREQ_SEL and FEEDBACK configuration to generate exact required frequencies from lower-cost crystal oscillators. Use Value: Replaces multiple fixed-ratio clock generators with one configurable device - lowers BOM count and supports multiple platform variants from single PCB design. |
Use Scenario: Delivering deterministic clock edges to FPGA-based motion controllers and real-time I/O modules in factory automation racks. IC Role / Device Role / Timing Role: MC88915FN55 operates in PLL test mode (PLL_EN = LOW) during system diagnostics, generating predictable divide-by-4/8 clocks from low-frequency test vectors. Use Value: Allows full functional validation of timing-critical logic at sub-MHz rates - essential for production test coverage without high-speed ATE equipment. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar clock distribution applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| MC88915FN70 | Higher 2X_Q max frequency (70 MHz vs. 55 MHz); identical pinout, package, and feature set | Supports faster CPU/memory subsystems requiring >55 MHz clocks; otherwise drop-in compatible | Select MC88915FN70 when system clock targets exceed 27.5 MHz and VCO headroom is needed |
| ICS557GI | Single 55 MHz 2X_Q output; no Q5 or Q/2 outputs; different PLL architecture (no FREQ_SEL or dual SYNC) | Lacks phase-inverted and divided outputs - unsuitable for designs requiring Q5 or Q/2 functionality | Choose ICS557GI only for simple fanout-only applications where Q5/Q/2 are unused and footprint compatibility is verified |
Compared with MC88915FN70, the MC88915FN55 trades 15 MHz 2X_Q headroom for cost and power efficiency in mid-range systems; compared with ICS557GI, it offers richer clock flexibility (Q5, Q/2, dual SYNC, FREQ_SEL) at the expense of higher pin count and layout complexity.
Availability
MC88915FN55 is available at Aetrix Electronics and suitable for workstation CPU clock distribution, multi-board synchronous systems, and legacy PC chipset timing requiring stable component supply and long-lifecycle support.
Supply support for MC88915FN55 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 pioneer in high-speed timing ICs, known for robust PLL architectures and industrial-grade reliability in computing and communications infrastructure.
The MC88915 belongs to Motorola's Timing Solutions product line, engineered specifically for low-skew, multi-output clock distribution in high-performance computing platforms where phase alignment and jitter control are critical.
FAQ
What is the maximum guaranteed 2X_Q output frequency for MC88915FN55?
The MC88915FN55 guarantees a maximum 2X_Q output frequency of 55 MHz under phase-locked conditions with 50 pF load. This specification is explicitly defined in the Frequency Specifications table (page 4) and applies only when the device is in steady-state PLL lock - not during startup or test mode. The Q0–Q4 outputs are accordingly limited to 27.5 MHz maximum.
How does the FREQ_SEL pin affect MC88915FN55 operation?
The FREQ_SEL pin selects the feedback division ratio inside the MC88915FN55 PLL: HIGH configures ÷1, LOW configures ÷2. When FREQ_SEL is LOW, the VCO runs at twice the feedback frequency, allowing the device to maintain optimal VCO operation (≥20 MHz) even with low-frequency SYNC inputs (as low as 2.5 MHz for 1:2 mode). This extends usable input range without external dividers.
Can MC88915FN55 operate without an external RC network on the RC1 pin?
No - the MC88915FN55 requires an external RC network connected to the RC1 pin to stabilize the PLL loop. Figure 6 specifies a 470 kΩ resistor and 0.1 µF capacitor as the standard configuration. Omitting this network causes excessive jitter and failure to achieve or maintain phase lock. For VCO frequencies below 40 MHz, Motorola recommends substituting a 1 MΩ resistor instead of 470 kΩ.
What is the purpose of the LOCK output on MC88915FN55?
The LOCK output on MC88915FN55 goes high when the PLL achieves steady-state phase and frequency lock. However, Motorola explicitly states it should be used only for passive monitoring or evaluation - not to drive active circuitry - because it may remain low even when phase-locked under certain conditions. Its behavior is not guaranteed during transients or edge cases, making it unsuitable for safety-critical or control-path applications.
Is MC88915FN55 compatible with modern 3.3 V systems?
No - the MC88915FN55 is a 5.0 V ±5% device with TTL-compatible inputs (VIH ≥2.0 V, VIL ≤0.8 V) and CMOS-level outputs capable of ±36 mA drive. It lacks 3.3 V tolerance or level-shifting capability. Interfacing with 3.3 V logic requires external level translators or voltage translators; direct connection risks overvoltage damage or unreliable signaling.
MC88915FN55 Specifications
- Product attributes
- Attribute value
- Manufacturer:
- NXP Semiconductors
- Series:
- -
- Package/Case:
- 28-LCC (J-Lead)
- Packaging:
- Tube
- 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)
MC88915FN55 FAQ
1.How can I place an order for MC88915FN55 through Aetrix?
Please submit a Request for Quotation (RFQ) for MC88915FN55 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 MC88915FN55 reliable?
The price and inventory of MC88915FN55 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for MC88915FN55 is usually 5 days.
3.What payment methods are accepted for MC88915FN55?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for MC88915FN55 transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for MC88915FN55?
MC88915FN55 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your MC88915FN55 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 MC88915FN55?
For technical support, including MC88915FN55 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your MC88915FN55 requirements.
6.How does Aetrix verify that MC88915FN55 is sourced from the original manufacturer or authorized distributors?
All MC88915FN55 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 MC88915FN55 meets industry standards.
7.What is the process for return or replacement of MC88915FN55?
All MC88915FN55 units undergo pre-shipment inspection (PSI). If there is an issue with MC88915FN55, 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 MC88915FN55 part is unused and in its original packaging.
Return procedure for MC88915FN55:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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