Analog Devices Inc. LT1424CS8-9#PBF

Overview

LT1424CS8-9#PBF from Analog Devices (formerly Linear Technology) is a monolithic isolated flyback switching regulator IC designed for PCMCIA Type II-compliant –9V isolated LAN supplies. It integrates a 1.6A peak-current switch, primary-side output voltage sensing, load compensation, and 285kHz fixed-frequency current-mode control - delivering up to 200mA at –9V without optoisolators or third-winding feedback.

For engineers reviewing the LT1424CS8-9#PBF datasheet, LT1424CS8-9#PBF pinout, LT1424CS8-9#PBF application, or LT1424CS8-9#PBF equivalent, key selection considerations include its 8-pin SO package, primary-side regulation architecture, shutdown current of 20µA, ±9V output capability in isolated topologies, and compatibility with compact height-constrained designs (≤2.41mm).

Technical Context

The LT1424CS8-9#PBF implements a proprietary flyback error amplifier that samples the primary-side flyback pulse waveform to derive isolated output voltage information - eliminating need for optoisolators or auxiliary windings. Its collapse-detect timing logic enables stable regulation down to discontinuous conduction mode.

It uses current-mode control with integrated slope compensation, features an externally programmable load compensation network via RCCOMP pin, and includes synchronized oscillator input (SYNC), shutdown control (SHDN), and dual ground separation (PGND/SGND) for noise immunity in high-isolation applications.

Key Specifications

Pinout & Package

LT1424CS8-9#PBF is housed in an 8-lead plastic SOIC (SO-8) package with standard 1.27mm pitch, JEDEC MS-012AC compliant, and rated θ_JA = 110°C/W.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar isolated flyback regulator applications.

Compared with LT1424CS8-9#PBF, LT1425CSW#PBF offers design flexibility at the cost of increased complexity and board area, while UCC28C42DR requires full secondary-side feedback and external power stage - neither matches the LT1424CS8-9#PBF's combination of integrated switch, primary-side regulation, and PCMCIA-compliant form factor.

Availability

LT1424CS8-9#PBF is available at Aetrix Electronics and suitable for isolated LAN supplies, industrial Ethernet interfaces, medical sensor biasing, and PCMCIA-compliant portable power systems requiring stable component supply and long-lifecycle availability.

Supply support for LT1424CS8-9#PBF 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

Analog Devices (acquired Linear Technology in 2017) is a global leader in high-performance analog, mixed-signal, and power management semiconductors - serving precision instrumentation, industrial automation, and communications markets.

The LT1424 family was developed specifically for compact, isolated flyback converters in portable and embedded systems - emphasizing primary-side regulation, minimal height, and robust light-load performance without optoisolators.

FAQ

What is the output voltage polarity and tolerance of the LT1424CS8-9#PBF?

The LT1424CS8-9#PBF is factory-trimmed for a nominal –9V output voltage. Its reference voltage at the VSW pin is specified as 9.15V (typical), which - after accounting for Schottky diode forward drop and transformer turns ratio - delivers –9V ±3% under full-load conditions. The device does not support positive output configurations; it is exclusively optimized for negative-rail isolated flyback topologies.

Does the LT1424CS8-9#PBF require an optoisolator or third-winding feedback?

No, the LT1424CS8-9#PBF does not require an optoisolator or third-winding feedback. It achieves isolated output regulation by directly sensing the primary-side flyback pulse waveform using an integrated flyback error amplifier. This architecture eliminates both components, reducing BOM cost, board area, and long-term reliability risks associated with optoisolator aging or winding misalignment.

What is the minimum load required for regulation on the LT1424CS8-9#PBF?

The LT1424CS8-9#PBF maintains regulation down to approximately 2–3mA output current in discontinuous conduction mode, enabled by its collapse-detect timing circuitry. Below this level, regulation degrades due to insufficient flyback pulse width relative to the minimum enable time (t_EN ≈ 180ns) and enable delay (t_ED ≈ 150ns). A 1.8kΩ preload resistor is recommended in the reference design to ensure stable operation above 5mA.

Can the LT1424CS8-9#PBF be synchronized to an external clock?

Yes, the LT1424CS8-9#PBF supports external synchronization via its SYNC pin (Pin 3). It accepts logic-level signals with 10–90% duty cycle across a 330–450kHz range, allowing EMI reduction through frequency dithering or alignment with system clocks. When unused, the SYNC pin must be tied to ground - leaving it floating may cause erratic oscillator behavior.

What package type and thermal characteristics apply to the LT1424CS8-9#PBF?

The LT1424CS8-9#PBF is supplied in an 8-lead plastic SOIC (SO-8) package with θ_JA = 110°C/W. Its maximum junction temperature is 145°C, and it operates across –40°C to +125°C ambient. The package features separate PGND (power ground) and SGND (signal ground) pins to minimize noise coupling - proper PCB layout with dedicated ground planes for each is essential for stable regulation and EMI performance.