Texas Instruments LM1881N

Overview

LM1881N from Texas Instruments is a video sync separator IC that extracts composite sync, vertical sync, burst/back porch, and odd/even field timing signals from NTSC, PAL, or SECAM composite video inputs (0.5–2 V_p-p). It operates from 5–12 V supply, delivers <10 mA supply current, supports horizontal scan rates up to 150 kHz, and provides edge-triggered vertical output for gen-locking video systems in broadcast equipment and set-top boxes.

For engineers reviewing the LM1881N datasheet, LM1881N pinout, LM1881N application, or LM1881N equivalent, key selection considerations include its AC-coupled composite input interface, RSET-programmable vertical timing, default-triggered vertical output for non-standard video sources (e.g., video games), and TTL-compatible open-collector outputs with 40 µA logic-high drive capability.

Technical Context

The LM1881N uses internal integration of the composite sync waveform to derive vertical sync pulses-its integrator charge current is set by an external RSET resistor (680 kΩ typical), directly controlling both vertical pulse width (190–300 µs) and default delay time (32–90 µs). The vertical output is edge-triggered on the rising edge of the first serration pulse, with fallback to default triggering if no serration occurs within the RSET-defined window.

It generates four synchronized timing outputs: composite sync (clamped at 1.5 V, threshold-separated by ~70 mV), vertical sync (open-collector, logic-low active), burst/back porch gate (4 µs nominal width), and odd/even field index (high = odd field, low = even field), all derived from a single composite video input without external clocking.

Key Specifications

Pinout & Package

LM1881N is supplied in an 8-pin PDIP package (9.81 mm × 6.35 mm), designed for through-hole prototyping and legacy video board assembly.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar video sync separation applications.

Compared with EL4583CN and MAX9586ASA+, the LM1881N offers unique RSET-based timing adaptability, default-triggered vertical output for non-standard sources, and full four-output sync separation-making it the only option supporting legacy video game timing, VGA-derived sync, and field-aware memory buffering in a single 5–12 V monolithic IC.

Availability

LM1881N is available at Aetrix Electronics and suitable for video cameras and recorders, broadcasting systems, and set-top boxes requiring stable component supply across long-lifecycle analog video designs.

Supply support for LM1881N 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 with over 90 years of analog innovation, delivering high-reliability signal chain and power management solutions for industrial, automotive, and communications markets.

The LM1881N belongs to TI's legacy video interface product line, engineered specifically for analog video timing recovery in broadcast, consumer, and computing equipment where robust sync extraction from noisy or non-standard composite sources is essential.

FAQ

What is the function of the RSET pin on the LM1881N?

The RSET pin (Pin 6) on the LM1881N sets the internal integrator charge current and oscillator frequency via an external resistor. With a typical 680 kΩ resistor, it configures vertical pulse width (190–300 µs) and default vertical delay (32–90 µs), enabling adaptation to NTSC, PAL, or custom video formats-including VGA-derived sync. This resistor directly determines timing behavior and must be selected per application requirements using TI's published RSET vs. pulse width curves.

Does the LM1881N support PAL video signals?

Yes, the LM1881N explicitly supports PAL video signals as stated in its official datasheet (SNLS384G). It extracts composite sync, vertical sync, burst/back porch, and odd/even field outputs from standard negative-going sync PAL broadcasts (Phase Alternating Line), operating across the same 0.5–2 V_p-p input range and 5–12 V supply as NTSC. No configuration changes are needed for PAL compatibility.

How does the LM1881N handle video signals without vertical serrations?

The LM1881N handles non-standard video signals lacking vertical serrations-such as those from video game consoles-using its default-triggered vertical output mode. When no serration pulse occurs within the RSET-defined time window, the internal integrator charges to voltage V2, triggering a vertical sync pulse after a programmable delay (32–90 µs). This ensures deterministic vertical timing even for irregular or proprietary video sources.

What is the purpose of the OEOUT pin on the LM1881N?

The OEOUT pin (Pin 7) on the LM1881N provides a TTL-level odd/even field identifier: high = odd field, low = even field. This output enables correct sequencing in interlaced video applications such as frame memory storage, line-accurate VBI data insertion, and field-synchronized digital processing. Its logic state toggles per field based on equalizing pulse detection and is synchronized to the vertical sync output.

Can the LM1881N operate from a 3.3 V supply?

No, the LM1881N cannot operate from a 3.3 V supply. Its absolute maximum supply voltage is 13.2 V, but its recommended operating range is strictly 5 V to 12 V DC per the datasheet (SNLS384G, Section 6.3). Operation below 5 V results in undefined behavior, failed sync detection, and loss of output drive capability-TI specifies no characterization or guarantee for 3.3 V use.