Analog Devices Inc. LT1424CS8-9#TRPBF

Overview

LT1424CS8-9#TRPBF from Analog Devices (formerly Linear Technology) is a monolithic isolated flyback switching regulator IC designed for primary-side sensing of –9V output voltage without optoisolator or third-winding transformer. It integrates a 1.6A peak-current switch, 285kHz oscillator, feedback amplifier, load compensation circuitry, and shutdown control. Delivers up to 200mA at –9V from 3V–20V input, meeting PCMCIA Type II height constraints (≤2.41mm).

For engineers reviewing the LT1424CS8-9#TRPBF datasheet, LT1424CS8-9#TRPBF pinout, LT1424CS8-9#TRPBF application, or LT1424CS8-9#TRPBF equivalent, key selection considerations include primary-side regulation architecture, fixed –9V output, discontinuous-mode stability, load compensation capability, and SO-8 thermal performance (θ_JA = 110°C/W).

Technical Context

The LT1424CS8-9#TRPBF implements current-mode control with a proprietary flyback error amplifier that samples the primary-side flyback pulse waveform to infer isolated –9V output voltage-eliminating optoisolators and auxiliary windings. Its collapse-detect timing logic enables stable regulation down to ~2–3mA load in discontinuous conduction mode.

It features integrated load compensation via external RCCOMP capacitor and internal transconductance amplifier (ΔV_RCCOMP/ΔI_SW = 1.5Ω), enabling dynamic correction of secondary-side impedance effects. Shutdown reduces supply current to 20µA typical, while SYNC pin supports external frequency synchronization from 330kHz to 450kHz.

Key Specifications

Pinout & Package

LT1424CS8-9#TRPBF is housed in an 8-lead plastic SO package (SO-8, 3.9mm × 4.9mm, 1.75mm max height), optimized for PCMCIA Type II mechanical constraints.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LT3748EMSE#TRPBF and UCC28740DR, the LT1424CS8-9#TRPBF uniquely delivers factory-trimmed –9V output with zero secondary feedback components-making it the only drop-in solution for height-constrained, opto-free isolated LAN supplies.

Availability

LT1424CS8-9#TRPBF is available at Aetrix Electronics and suitable for PCMCIA Type II LAN modules, isolated Ethernet interfaces, CAN transceiver biasing, and medical sensor isolation requiring stable component supply and long-lifecycle support.

Supply support for LT1424CS8-9#TRPBF 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 for precision signal chain and power applications.

The LT1424CS8-9#TRPBF belongs to Linear's legacy isolated flyback controller family, engineered specifically for compact, optocoupler-free DC/DC conversion in space-constrained portable and interface applications.

FAQ

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

The LT1424CS8-9#TRPBF is configured for a fixed –9V output, with typical regulation of ±1.5% over temperature and load. Its internal reference is trimmed to 9.15V at the VSW pin, which-accounting for Schottky diode drop and transformer turns ratio-delivers –9.00V at the output under nominal conditions. The datasheet specifies VREF = 9.00V to 9.30V, translating to –9V ±3% in final application circuits.

Does the LT1424CS8-9#TRPBF require an external MOSFET?

No, the LT1424CS8-9#TRPBF integrates a high-current NPN bipolar switch rated for 1.6A peak current and 35V breakdown-sufficient to deliver 200mA at –9V without any external power devices. This integration eliminates gate-drive complexity and layout sensitivity associated with external MOSFETs, simplifying design for low-to-medium power isolated supplies.

How does the LT1424CS8-9#TRPBF achieve regulation without an optoisolator?

The LT1424CS8-9#TRPBF achieves regulation by sampling the flyback voltage pulse at the VSW pin during transformer reset. Its proprietary flyback error amplifier converts this pulse into a current proportional to output voltage, referenced to an internal 1.25V bandgap. This eliminates reliance on secondary-side feedback-removing optoisolator latency, CTR drift, and aging concerns inherent in traditional isolated designs.

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

Yes, the LT1424CS8-9#TRPBF includes a dedicated SYNC pin (Pin 3) that accepts TTL/CMOS-compatible square waves from 330kHz to 450kHz. When driven with a valid external clock (≥1.5V amplitude, 10–90% duty cycle), the internal 285kHz oscillator locks precisely-enabling EMI reduction through frequency dithering or alignment with system clocks in multi-rail power architectures.

What is the minimum load requirement to maintain regulation with the LT1424CS8-9#TRPBF?

The LT1424CS8-9#TRPBF maintains regulation down to approximately 2–3mA load in discontinuous conduction mode, enabled by its collapse-detect circuitry and minimum enable time logic. In the reference PCMCIA application, a 1.8kΩ preload resistor ensures 5mA minimum load-guaranteeing stable –9V output across all operating conditions without external biasing circuitry.