Analog Devices Inc. LT1424IS8-9#TRPBF

Overview

LT1424IS8-9#TRPBF 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 transformers.

For engineers reviewing the LT1424IS8-9#TRPBF datasheet, LT1424IS8-9#TRPBF pinout, LT1424IS8-9#TRPBF application, or LT1424IS8-9#TRPBF equivalent, key selection considerations include its primary-side regulation architecture, 2.8V–20V input range, shutdown current of 20µA, SO-8 package compatibility, and fixed –9V output targeting isolated Ethernet and portable interface power rails.

Technical Context

The LT1424IS8-9#TRPBF implements a proprietary flyback error amplifier that samples the primary-side flyback pulse waveform to infer isolated output voltage - eliminating need for optocouplers or auxiliary windings. Its collapse-detect timing logic enables stable regulation down to ~2mA load in discontinuous conduction mode.

It uses current-mode control with internal slope compensation, features a dedicated RCCOMP pin for external load-compensation capacitor (0.1µF typical), and includes programmable shutdown (SHDN pin threshold: 0.3–1.3V) and SYNC input (330–450kHz synchronization range) - all operating across –40°C to 125°C junction temperature.

Key Specifications

Pinout & Package

LT1424IS8-9#TRPBF is housed in an 8-lead plastic SOIC (SO-8) package with standard 1.27mm pitch, JEDEC MS-012AC compliant, and rated for θ_JA = 110°C/W.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LT3748IMS#TRPBF and UCC28911DR, the LT1424IS8-9#TRPBF offers optimal integration for low-voltage DC-fed isolated –9V supplies - combining minimal component count, PCMCIA-compliant height, and load-compensated regulation without sacrificing thermal performance in SO-8.

Availability

LT1424IS8-9#TRPBF is available at Aetrix Electronics and suitable for isolated Ethernet interfaces, PCMCIA peripheral power, portable medical sensor rails, and industrial CAN bias supplies requiring stable component supply and long-term manufacturability.

Supply support for LT1424IS8-9#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 - serving precision instrumentation, industrial automation, communications, and healthcare markets.

The LT1424 family was developed specifically for compact, low-profile isolated DC/DC conversion in portable and interface applications - emphasizing primary-side regulation, minimal external components, and robust light-load behavior.

FAQ

What is the output voltage tolerance of the LT1424IS8-9#TRPBF under full load and temperature?

The LT1424IS8-9#TRPBF delivers a nominal –9V output with ±5% regulation over –40°C to 125°C junction temperature and 0–200mA load, as verified by load compensation and factory calibration of internal thin-film resistors. Output accuracy includes contributions from Schottky diode VF drift and transformer leakage inductance, but remains within spec per Typical Application Circuit TPC1424 TA01.

Does the LT1424IS8-9#TRPBF require an external MOSFET or can it drive the transformer directly?

The LT1424IS8-9#TRPBF integrates a high-current NPN bipolar switch rated for 1.6A peak current and 35V breakdown - enabling direct connection to the transformer primary without external MOSFETs. It delivers up to 200mA at –9V using only passive external components (transformer, diode, capacitors, and 0.1µF RCCOMP cap).

How does the LT1424IS8-9#TRPBF achieve regulation without an optocoupler or third winding?

The LT1424IS8-9#TRPBF achieves regulation by sampling the amplitude of the primary-side flyback pulse at the VSW pin - converting it to a proportional current via internal RFB and Q1, then comparing it to the 1.22V bandgap reference. This pseudo-DC feedback method eliminates reliance on secondary-side signals, confirmed in Block Diagram 1424BD and Operation Section pages 8–9 of the datasheet.

What is the minimum load required for stable regulation with the LT1424IS8-9#TRPBF?

The LT1424IS8-9#TRPBF maintains regulation down to ~2–3mA due to its collapse-detect circuitry and minimum flyback enable time (tEN = 180ns). In the reference PCMCIA application, a 1.8kΩ preload resistor ensures 5mA minimum load - preventing loss of regulation during idle periods while staying within height constraints.

Can the LT1424IS8-9#TRPBF be synchronized to an external clock, and what is the acceptable frequency range?

Yes, the LT1424IS8-9#TRPBF supports external synchronization via the SYNC pin (Pin 3), accepting logic-level square waves from 330kHz to 450kHz - allowing EMI reduction through frequency alignment. The internal oscillator is disabled when SYNC is active, and the part retains full regulation performance across this range per Electrical Characteristics Table on page 3.