Texas Instruments LMH1982SQ/NOPB

Overview

LMH1982SQ/NOPB from Texas Instruments is a multi-rate video clock generator IC designed for genlock synchronization in broadcast video systems. It delivers two simultaneous LVDS output clocks (SD_CLK at 27/67.5 MHz and HD_CLK at 74.25/74.176/148.5/148.35 MHz), a programmable Top of Frame (TOF) pulse, and dual reference inputs (REF_A/REF_B) with H/V sync support - enabling precise frame-aligned timing in 3G-SDI SerDes, FPGA-based video capture, and triple-rate SDI equipment.

For engineers reviewing the LMH1982SQ/NOPB datasheet, LMH1982SQ/NOPB pinout, LMH1982SQ/NOPB application, or LMH1982SQ/NOPB equivalent, key selection considerations include its dual PLL architecture (VCXO-based PLL1 + integrated-VCO PLL2–4), sub-50 ps peak-to-peak jitter on HD_CLK outputs, I²C programmability, free-run/holdover behavior on reference loss, and WQFN-32 package compatibility with high-density video PCB layouts.

Technical Context

The LMH1982SQ/NOPB implements a two-stage analog PLL architecture: PLL1 uses an external 27 MHz VCXO and loop filter to achieve low-jitter genlock to H/V sync references, while PLL2–4 use integrated VCOs to generate SD/HD clocks with fixed multiplication ratios (e.g., ×2.75, ×5.5, ×2.5). Its reference decoder supports NTSC, PAL, 720p, 1080i/p, and AES47 sample clock formats via programmable dividers and line/frame counters.

Genlock operation enables cross-locking between input references and output clocks, with configurable lock detection, NO_REF/NO_LOCK status flags, and programmable TOF timing offset (e.g., TOF_OFFSET = 262 for NTSC). Free-run mode relies on the VC_FREERUN analog control voltage to set VCXO frequency accuracy when reference is lost, while holdover maintains short-term phase stability via loop filter charge retention.

Key Specifications

Pinout & Package

The LMH1982SQ/NOPB is housed in a 5.0 mm × 5.0 mm, 32-pin WQFN package with exposed die attach pad (DAP) connected to GND for thermal and electrical integrity. Pin functions are validated per TI SNLS289D Rev D datasheet.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar multi-rate video clock generation applications.

Compared with LMH1982SQ/NOPB, LMH1981 provides only reference separation-not clock synthesis-while Si5338A-D-GM offers broader frequency flexibility but no native H/V sync decoding or TOF pulse logic, making LMH1982SQ/NOPB uniquely suited for SMPTE-compliant genlock in broadcast hardware.

Availability

LMH1982SQ/NOPB is available at Aetrix Electronics and suitable for broadcast infrastructure, FPGA-based video SerDes, and triple-rate SDI equipment requiring stable component supply, long-term lifecycle support, and traceable sourcing for production programs.

Supply support for LMH1982SQ/NOPB 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 connectivity technologies for industrial, automotive, and communications markets.

The LMH1982SQ/NOPB belongs to TI's broadcast video timing product line, engineered specifically for SMPTE-compliant genlock, frame-accurate TOF generation, and multi-standard SDI clock synthesis in professional video equipment.

FAQ

What video standards does the LMH1982SQ/NOPB support for genlock operation?

The LMH1982SQ/NOPB supports NTSC (525i), PAL (625i), 720p (24–60 Hz), 1080i/p (23.98–60 Hz), and AES47 48 kHz sample clock formats. It decodes H/V sync timing from analog or digital references and configures internal PLL dividers (e.g., REF_DIV_SEL, TOF_LPFM) to match frame/line structures - enabling precise genlock across SD, HD, and 3G-SDI systems without external timing processors.

How does the LMH1982SQ/NOPB handle loss of reference input?

Upon loss of reference, the LMH1982SQ/NOPB enters either Free Run or Holdover mode based on configuration. In Free Run mode, the VC_FREERUN pin voltage sets VCXO frequency accuracy; in Holdover mode, the LPF pin retains charge to maintain short-term phase stability. Both modes preserve output clock continuity while allowing system-level failover to REF_B or backup timing sources - critical for broadcast uptime.

Can the LMH1982SQ/NOPB generate TOF pulses for both SD and HD formats simultaneously?

Yes - the LMH1982SQ/NOPB generates a single TOF pulse synchronized to the selected output format (e.g., NTSC, 1080p/24), but its programmable TOF_CLK, TOF_PPL, and TOF_OFFSET registers allow TOF timing to be derived from either the 27 MHz SD_CLK or native HD_CLK frequencies. This enables frame-accurate TOF alignment across all supported SD/HD formats without hardware changes.

What is the role of the external loop filter connected to the LPF pin on the LMH1982SQ/NOPB?

The LPF pin drives an external RC loop filter that controls PLL1's bandwidth, lock time, and jitter transfer characteristics. A narrow filter bandwidth (e.g., ~10 Hz) attenuates input reference jitter but increases lock time; a wider bandwidth (e.g., ~100 Hz) improves lock speed at the cost of higher jitter transfer. This user-adjustable design allows optimization for specific broadcast system requirements.

Does the LMH1982SQ/NOPB require an external VCXO, and what specifications must it meet?

Yes - the LMH1982SQ/NOPB requires an external 27.0000 MHz VCXO connected to the VCXO pin (Pin 29). The VCXO must support ±100 ppm tuning range and exhibit low phase noise (≤−140 dBc/Hz at 10 kHz offset) to ensure HD_CLK jitter remains below 50 ps peak-to-peak. TI recommends using a 27 MHz VCXO with compatible control voltage range matching the VC_FREERUN input specification.