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Home > Products > Integrated Circuits (ICs) > Clock/Timing > Application Specific Clock/Timing

Texas Instruments LMKDB1204REXT

Name: LMKDB1204REXT
Brand: Texas Instruments
SKU: LMKDB1204REXT
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: LMKDB1204REXT

Manufacturer:: Texas Instruments

Category:: Application Specific Clock/Timing

Package:: 28-QFN

Datasheet:: LMKDB1204REXT.pdf

Description:: 2-INPUT 4-OUTPUT LP-HCSL CLOCK M

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Product details

Overview

LMKDB1204REXT from Texas Instruments is a dual-input, 4-output PCIe Gen 1–7 ultra-low-jitter LP-HCSL clock multiplexer supporting Common Clock (CC) and Independent Reference (IR) architectures with fail-safe inputs, 85Ω/100Ω selectable output impedance, and 1.8V/3.3V ±10% supply operation for server motherboard timing distribution.

For engineers reviewing the LMKDB1204REXT datasheet, LMKDB1204REXT pinout, LMKDB1204REXT application, or LMKDB1204REXT equivalent, this device delivers PCIe Gen 7–compliant additive jitter down to 2.1 fs RMS (12 kHz–20 MHz), SMBus + Side-Band Interface control, loss-of-signal detection, and flexible power-up sequencing in a 4 mm × 4 mm VQFN-28 package.

Technical Context

The LMKDB1204REXT implements a dual-differential-clock-input mux architecture with automatic input selection logic and independent output enable control per channel. It supports both CC and IR PCIe topologies and accepts input clocks with or without spread-spectrum modulation (SSC).

Its timing path integrates low-noise LP-HCSL drivers with programmable slew-rate control, fail-safe input monitoring, and integrated LOS detection. The device uses internal pullup/pulldown resistors on control pins and supports SMBus register access alongside high-speed SBI for dynamic output enable/disable.

Key Specifications

Parameter	Value and Actual Design Meaning
PCIe Support	Gen 1 through Gen 7 - fully compliant with DB2000QL timing and functional requirements for next-gen high-speed interconnects.
Additive Jitter (RMS)	2.1 fs @ PCIe Gen 7 - enables robust signal integrity margin at 64 GT/s data rates with minimal timing uncertainty.
Output Count / Type	4 LP-HCSL differential outputs - each independently controllable via OE# pins or SBI interface for dynamic clock gating.
Input Configuration	Dual differential clock inputs (CLKIN_P/N, CLKIN2_P/N) - supports redundancy, failover, or IR/CC topology selection.
Output Impedance	Selectable 85Ω or 100Ω - matches standard PCB trace impedances for optimal LP-HCSL signal integrity without external termination.
Supply Voltage	1.8V or 3.3V ±10% - dual-rail support enables compatibility with mixed-voltage system designs and power optimization.
Operating Temp	–40°C to +105°C ambient - qualified for industrial-grade server and accelerator applications with extended thermal margins.

Pinout & Package

LMKDB1204REXT is housed in a 4 mm × 4 mm VQFN-28 package (REX) with exposed thermal pad. Pin functions are defined per TI SNAS855G Rev May 2026, with dedicated differential clock I/O, SMBus interface, SBI control, and individual output enable signals.

Pin/Terminal	Circuit Role	Design Meaning
CLKIN_P / CLKIN_N	Differential clock input A	Primary reference input; supports SSC and failsafe monitoring; used in CC or IR mode.
CLKIN2_P / CLKIN2_N	Differential clock input B	Secondary reference input; enables automatic input failover or IR topology implementation.
CLK0_P / CLK0_N – CLK3_P / CLK3_N	LP-HCSL differential outputs	Four fully buffered, slew-rate-configurable clock outputs; each pair drives one PCIe lane group.
^OE0# – ^OE3#	Active-low output enable controls	Individual hardware control of each output; internal pullup ensures safe default disable state.
SMB_DATA / SMB_CLK	SMBus interface	Two-wire bus for configuration register access, status readback, and dynamic parameter adjustment.
vSBI_EN, ^/vOE2#/SBI_OUT, ^/vOE3#/SBI_CLK, ^/vOE4#/SBI_IN	Side-Band Interface signals	High-speed serial interface enabling sub-μs output enable/disable without SMBus transaction overhead.
LOS#	Loss-of-Signal indicator	Open-drain active-low flag signaling invalid input clock; requires external pullup for system-level fault reporting.
VDDA / VDDCLK / GND	Analog & output power / ground	Separate analog (VDDA) and output (VDDCLK) rails reduce noise coupling; thermal pad improves thermal performance.

Key Features

Feature	Design Value
Dual-input PCIe clock mux	Enables seamless switching between primary and backup clock sources or CC/IR topology selection without glitching.
2.1 fs Gen 7 additive jitter	Meets PCIe Gen 7 timing budget for 64 GT/s links, preserving eye opening and reducing bit error rate in high-density systems.
Fail-safe input monitoring	Guarantees deterministic output behavior during input loss or instability-critical for system boot reliability and hot-plug robustness.
85Ω/100Ω output impedance select	Eliminates need for external series termination resistors; simplifies layout and reduces BOM count across diverse board stackups.
SMBus + SBI dual-control interface	Combines configurability (SMBus) with real-time responsiveness (SBI), enabling both initialization and runtime clock management.
–40°C to +105°C operation	Validated for deployment in thermally demanding server chassis and AI accelerator modules without derating.

Applications

PCIe Gen 7 Server Motherboard	NIC/SmartNIC Timing Distribution
Use Scenario: Distributing low-jitter reference clocks to 4 PCIe Gen 7 x16 slots and associated retimers on a dual-socket server motherboard. IC Role / Device Role / Timing Role: Dual-input clock mux providing redundant, failover-capable LP-HCSL clocks with Gen 7–compliant jitter performance. Use Value: Enables simultaneous operation of multiple Gen 7 devices while maintaining PCIe compliance and eliminating timing-related link training failures.	Use Scenario: Driving four independent LP-HCSL clock domains for multi-port 400G SmartNICs with separate PHY lanes and packet processing subsystems. IC Role / Device Role / Timing Role: Low-additive-jitter clock buffer/mux delivering synchronized, isolated clock trees to discrete NIC subsystems. Use Value: Reduces inter-lane skew and jitter accumulation across high-bandwidth data paths, improving throughput consistency and latency predictability.
Hardware Accelerator Rack Card	AI Training Cluster Interconnect
Use Scenario: Providing phase-aligned, low-noise clocks to FPGA-based accelerators and attached HBM2E memory controllers on a PCIe-based rack card. IC Role / Device Role / Timing Role: PCIe Gen 7–compliant clock mux with fail-safe inputs ensuring reliable operation during FPGA reconfiguration or thermal throttling events. Use Value: Prevents clock-related resets or data corruption during dynamic workload shifts, increasing accelerator uptime and computational efficiency.	Use Scenario: Synchronizing clock domains across multiple GPU/CPU nodes interconnected via PCIe Gen 7 switch fabrics in distributed AI training clusters. IC Role / Device Role / Timing Role: Ultra-low-jitter clock distribution IC supporting IR architecture to minimize inter-node timing drift under variable load conditions. Use Value: Improves collective gradient synchronization accuracy and reduces training iteration variance across heterogeneous compute nodes.

PCIe Gen 7 Server Motherboard

NIC/SmartNIC Timing Distribution

Use Scenario: Distributing low-jitter reference clocks to 4 PCIe Gen 7 x16 slots and associated retimers on a dual-socket server motherboard.

IC Role / Device Role / Timing Role: Dual-input clock mux providing redundant, failover-capable LP-HCSL clocks with Gen 7–compliant jitter performance.

Use Value: Enables simultaneous operation of multiple Gen 7 devices while maintaining PCIe compliance and eliminating timing-related link training failures.

Use Scenario: Driving four independent LP-HCSL clock domains for multi-port 400G SmartNICs with separate PHY lanes and packet processing subsystems.

IC Role / Device Role / Timing Role: Low-additive-jitter clock buffer/mux delivering synchronized, isolated clock trees to discrete NIC subsystems.

Use Value: Reduces inter-lane skew and jitter accumulation across high-bandwidth data paths, improving throughput consistency and latency predictability.

Hardware Accelerator Rack Card

AI Training Cluster Interconnect

Use Scenario: Providing phase-aligned, low-noise clocks to FPGA-based accelerators and attached HBM2E memory controllers on a PCIe-based rack card.

IC Role / Device Role / Timing Role: PCIe Gen 7–compliant clock mux with fail-safe inputs ensuring reliable operation during FPGA reconfiguration or thermal throttling events.

Use Value: Prevents clock-related resets or data corruption during dynamic workload shifts, increasing accelerator uptime and computational efficiency.

Use Scenario: Synchronizing clock domains across multiple GPU/CPU nodes interconnected via PCIe Gen 7 switch fabrics in distributed AI training clusters.

IC Role / Device Role / Timing Role: Ultra-low-jitter clock distribution IC supporting IR architecture to minimize inter-node timing drift under variable load conditions.

Use Value: Improves collective gradient synchronization accuracy and reduces training iteration variance across heterogeneous compute nodes.

Equivalent & Alternatives

The following parts are listed as comparable options for similar PCIe clock mux applications.

Alternative Part	Technical Difference	Application Difference	Selection Advice
LMKDB1204Z85	Fixed 85Ω output impedance; no impedance select option; identical pinout and functionality otherwise.	Best suited for designs where 85Ω routing is standardized and no flexibility is needed.	Select LMKDB1204Z85 when board layout mandates fixed 85Ω termination and SMBus/SBI control is not required.
LMKDB1204Z100	Fixed 100Ω output impedance; lacks impedance-select capability; same package and electrical specs otherwise.	Ideal for systems using 100Ω-controlled impedance traces, such as certain backplane or mezzanine interfaces.	Choose LMKDB1204Z100 for 100Ω-optimized layouts where output impedance must be fixed and consistent across all channels.

Compared with LMKDB1204Z85 and LMKDB1204Z100, the LMKDB1204REXT provides field-programmable output impedance selection-enabling single-BOM support across 85Ω and 100Ω routing variants without redesign or inventory fragmentation.

Availability

LMKDB1204REXT is available at Aetrix Electronics and suitable for PCIe Gen 7 server motherboards, SmartNIC timing distribution, and AI accelerator rack cards requiring stable component supply, long-term lifecycle assurance, and full DB2000QL compliance.

Supply support for LMKDB1204REXT 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

Texas Instruments is a global semiconductor leader specializing in analog, embedded processing, and clock solutions for high-performance computing and infrastructure markets.

The LMKDB family was designed specifically for PCIe Gen 1–7 timing distribution in servers, accelerators, and networking equipment-emphasizing ultra-low jitter, architectural flexibility (CC/IR), and robust system-level fault handling.

FAQ

What PCIe generations does the LMKDB1204REXT support?

The LMKDB1204REXT supports PCIe Gen 1 through Gen 7, meeting all DB2000QL specifications including additive jitter limits (2.1 fs RMS for Gen 7), input sensitivity, and output drive strength. Its architecture is validated for CC and IR topologies and accepts spread-spectrum clocking on either input without degradation.

Does the LMKDB1204REXT require external termination resistors?

No, the LMKDB1204REXT does not require external termination resistors. Its LP-HCSL outputs feature internally selectable 85Ω or 100Ω output impedance, matching standard PCB trace impedances directly. This eliminates series resistors, reduces layout complexity, and improves signal integrity across varying stackup configurations.

How does the SBI interface differ from SMBus on the LMKDB1204REXT?

The SBI (Side-Band Interface) on the LMKDB1204REXT enables sub-microsecond output enable/disable transitions using dedicated high-speed serial signals (SBI_IN, SBI_CLK, SBI_OUT), whereas SMBus relies on packetized two-wire communication with higher latency. SBI is ideal for dynamic clock gating during runtime, while SMBus handles configuration, status, and non-critical register access.

What is the function of the LOS# pin on the LMKDB1204REXT?

The LOS# (Loss of Signal) pin on the LMKDB1204REXT is an open-drain active-low output that asserts low when the selected input clock fails validation-indicating loss of valid differential swing, frequency deviation, or excessive jitter. It requires an external pullup resistor and connects directly to system fault-monitoring logic for automated recovery or alerting.

Is the LMKDB1204REXT pin-compatible with any Intel clock buffer standards?

The LMKDB1204REXT is not pin-compatible with Intel DB2000QL or DB1206 devices, as those are 20- and 12-output buffers respectively. However, it is DB2000QL-compliant in timing, jitter, and functional behavior-ensuring interoperability in PCIe Gen 7 systems where architectural fit (dual-input mux vs. single-input buffer) is prioritized over mechanical pin mapping.

LMKDB1204REXT Specifications

Product attributes: Attribute value

Manufacturer:: Texas Instruments

Series:: LMKDB1xxx

Package/Case:: 28-QFN

Packaging:: Tape & Reel (TR)

Product Status:: Active

Programmable:: -

PLL:: No

Main Purpose:: PCI Express (PCIe)

Input:: LP-HCSL

Output:: LP-HCSL

Number of Circuits:: 1

Ratio - Input:Output:: 2:4

Differential - Input:Output:: Yes/Yes

Frequency - Max:: 400MHz

Voltage - Supply:: 1.71V ~ 1.89V, 2.97V ~ 3.6V

Operating Temperature:: -40°C ~ 105°C (TA)

Mounting Type:: Surface Mount

Grade:: -

Qualification:: -

Supplier Device Package:: 28-VQFN (4x4)

LMKDB1204REXT FAQ

1.How can I place an order for LMKDB1204REXT through Aetrix?

Please submit a Request for Quotation (RFQ) for LMKDB1204REXT 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 LMKDB1204REXT reliable?

The price and inventory of LMKDB1204REXT are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LMKDB1204REXT is usually 5 days.

3.What payment methods are accepted for LMKDB1204REXT?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LMKDB1204REXT transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for LMKDB1204REXT?

LMKDB1204REXT orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your LMKDB1204REXT 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 LMKDB1204REXT?

For technical support, including LMKDB1204REXT datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LMKDB1204REXT requirements.

6.How does Aetrix verify that LMKDB1204REXT is sourced from the original manufacturer or authorized distributors?

All LMKDB1204REXT 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 LMKDB1204REXT meets industry standards.

7.What is the process for return or replacement of LMKDB1204REXT?

All LMKDB1204REXT units undergo pre-shipment inspection (PSI). If there is an issue with LMKDB1204REXT, 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 LMKDB1204REXT part is unused and in its original packaging.

Return procedure for LMKDB1204REXT:

1.Submit a request within 90 days.

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

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