Analog Devices Inc. LT8304IS8E-1#PBF

Overview

LT8304IS8E-1#PBF from Analog Devices (formerly Linear Technology) is a monolithic micropower isolated flyback controller IC with integrated 150V/2A DMOS switch, operating from 3V to 100V input and delivering up to 24W isolated output power. It enables opto-isolator–free regulation via primary-side flyback waveform sampling, supports boundary mode for tight load regulation, and features low-ripple Burst Mode operation with 116µA sleep current - ideal for auxiliary/housekeeping supplies in industrial and telecom systems.

For engineers reviewing the LT8304IS8E-1#PBF datasheet, LT8304IS8E-1#PBF pinout, LT8304IS8E-1#PBF application, or LT8304IS8E-1#PBF equivalent, key selection considerations include its 150V switch rating, 390µA active-mode quiescent current, 1.00V internal RREF reference, 315–385kHz max switching frequency, and thermal-enhanced 8-lead SO package with exposed GND pad.

Technical Context

The LT8304IS8E-1#PBF implements quasi-resonant boundary conduction mode at heavy loads-turning on the switch at the SW node valley when secondary current reaches zero-to minimize transformer size and eliminate subharmonic oscillation. Its sample-and-hold error amplifier directly regulates isolated output voltage by sensing the flyback pulse amplitude across RFB, eliminating need for third winding or opto-isolator.

Unlike the base LT8304, the -1 variant features extended minimum switch-on time (950ns vs. 160ns) and enhanced immunity to primary-side current ringing in high step-up (≥5:1 turns ratio) applications. It maintains identical 116µA sleep current, 390µA active current, and 150V/2A switch specs while optimizing stability under high-VIN, light-load conditions.

Key Specifications

Pinout & Package

LT8304IS8E-1#PBF is housed in an 8-lead plastic SOIC package (S8E) with exposed GND pad (Pin 9), requiring soldering to PCB ground plane for thermal and electrical integrity.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LT8304IS8E#PBF, the LT8304IS8E-1#PBF trades faster minimum on-time for superior high-step-up stability, while UCC28740DR offers higher voltage capability at the cost of added component count and no built-in temperature compensation.

Availability

LT8304IS8E-1#PBF is available at Aetrix Electronics and suitable for industrial PLC power, medical isolated bias, telecom housekeeping, and automotive body control applications requiring stable component supply, long-term lifecycle support, and guaranteed –40°C to +125°C operation.

Supply support for LT8304IS8E-1#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 and maintains its high-performance power management portfolio with rigorous automotive, industrial, and medical qualification standards.

The LT8304 family is designed specifically for simplified, low-component-count isolated flyback power supplies - targeting applications where opto-isolator elimination, micropower operation, and primary-side regulation are critical design requirements.

FAQ

What is the maximum input voltage supported by the LT8304IS8E-1#PBF?

The LT8304IS8E-1#PBF supports an absolute maximum input voltage of 100V on the VIN pin, with continuous operation specified from 3V to 100V. The internal 150V DMOS switch allows safe operation with transient spikes up to 150V on the SW pin, provided proper transformer leakage inductance management is implemented to keep flyback voltage spikes below this limit. This makes the LT8304IS8E-1#PBF suitable for harsh industrial and telecom environments where input surges occur.

How does the LT8304IS8E-1#PBF achieve regulation without an opto-isolator?

The LT8304IS8E-1#PBF achieves regulation by sampling the isolated output voltage directly from the primary-side flyback waveform across the RFB resistor. During boundary or discontinuous conduction mode, the SW node voltage rises to (VOUT × NPS) + VIN when the secondary current reaches zero - a point where parasitic impedance effects vanish. The LT8304IS8E-1#PBF's internal sample-and-hold error amplifier captures this clean voltage representation, eliminating the need for opto-isolators or third-winding feedback. This method improves reliability and reduces component count versus traditional isolated topologies.

What is the purpose of the TC pin on the LT8304IS8E-1#PBF?

The TC pin on the LT8304IS8E-1#PBF provides a proportional-to-absolute-temperature (PTAT) voltage (3.35mV/°C, 1.00V at 25°C) used to compensate for the negative temperature coefficient of the output diode's forward voltage (VF). By connecting an RTC resistor between TC and RREF pins, a PTAT current offsets VF drift - critical for maintaining ±2% output accuracy across temperature in low-VOUT applications like 3.3V or 5V supplies. Without TC compensation, VF drift alone can cause >300mV error over –40°C to +125°C.

Can the LT8304IS8E-1#PBF replace the LT8304IS8E#PBF in existing designs?

The LT8304IS8E-1#PBF is pin-compatible and functionally compatible with the LT8304IS8E#PBF but features a longer minimum switch-on time (950ns vs. 160ns) optimized for high step-up (≥5:1) applications. In designs with ≤4:1 transformer turns ratios and well-controlled SW node ringing, direct replacement is possible. However, in high-VIN, light-load scenarios with aggressive step-up, the LT8304IS8E-1#PBF prevents false current-limit triggering - making it the preferred choice for new designs targeting robustness in demanding isolated flyback implementations.

What thermal considerations apply to the LT8304IS8E-1#PBF package?

The LT8304IS8E-1#PBF uses an 8-lead SOIC package (S8E) with an exposed GND pad (Pin 9) that must be soldered to the PCB ground plane for effective thermal dissipation. With θJA = 33°C/W, the device achieves reliable operation up to +125°C junction temperature. For continuous 24W output, thermal vias under the exposed pad and a minimum 1-inch² copper pour are recommended. The TC pin voltage can be monitored to estimate real-time junction temperature - enabling dynamic derating or thermal warning in safety-critical systems.