Analog Devices Inc. LT8304HS8E-1#PBF

Overview

LT8304HS8E-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 and low-ripple Burst Mode® operation, and targets high step-up applications such as 4V–80V_IN/5V_OUT auxiliary supplies in industrial and automotive systems.

For engineers reviewing the LT8304HS8E-1#PBF datasheet, LT8304HS8E-1#PBF pinout, LT8304HS8E-1#PBF application, or LT8304HS8E-1#PBF equivalent, key selection criteria include its –40°C to 150°C junction temperature rating, 116µA sleep-mode quiescent current, 315–385kHz switching frequency range, 950ns minimum on-time (LT8304-1 variant), and thermally enhanced 8-lead SO package with exposed GND pad.

Technical Context

The LT8304HS8E-1#PBF implements quasi-resonant boundary conduction mode at heavy load-turning on the internal switch at the SW node valley when secondary current reaches zero-to achieve tight load regulation without third-winding sensing. Its sample-and-hold error amplifier captures the isolated output voltage directly from the flyback pulse amplitude, eliminating opto-isolators and reducing component count.

At light loads, it transitions to low-ripple Burst Mode® operation with 11kHz minimum frequency, maintaining >80% efficiency down to 0.5% full-load while minimizing output voltage ripple. The LT8304-1 variant features extended blanking time immunity to primary-side current ringing, making it specifically suited for ≥5:1 step-up transformer ratios in high-V_IN/low-I_OUT configurations.

Key Specifications

Pinout & Package

LT8304HS8E-1#PBF is housed in an 8-lead plastic SO package (S8E) with exposed thermal pad (Pin 9, GND). The exposed pad must be soldered to PCB ground plane for thermal and electrical integrity. θ_JA = 33°C/W.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LT8304IS8E-1#PBF, the LT8304HS8E-1#PBF delivers guaranteed operation up to 150°C junction temperature-critical for space-constrained, high-ambient designs-while UCC28740DR offers broader design flexibility at the cost of added components and reduced integration.

Availability

LT8304HS8E-1#PBF is available at Aetrix Electronics and suitable for industrial auxiliary power, automotive housekeeping supplies, medical isolated sensors, and telecom remote PHY power requiring stable component supply across extended temperature and high-reliability use cases.

Supply support for LT8304HS8E-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) is a global leader in high-performance analog, mixed-signal, and power management semiconductors.

The LT8304 family was designed specifically for micropower, isolated flyback power conversion-enabling compact, reliable, and opto-free auxiliary supplies in harsh-environment applications where size, efficiency, and temperature resilience are critical.

FAQ

What is the maximum input voltage rating for the LT8304HS8E-1#PBF?

The LT8304HS8E-1#PBF has an absolute maximum input voltage rating of 100V on the VIN pin. It operates continuously over a 3V to 100V input range, making it suitable for wide-input applications including automotive battery rails and industrial 24V/48V systems with transients. The SW pin is rated for 150V transients, but design must ensure flyback voltage spikes remain within this limit using appropriate transformer leakage control.

How does the LT8304HS8E-1#PBF achieve isolated output regulation without an optocoupler?

The LT8304HS8E-1#PBF samples the isolated output voltage directly from the primary-side flyback waveform at the SW pin. When the secondary current reaches zero, the flyback pulse amplitude equals (V_OUT + V_F) × N_PS, which is converted to a current by the RFB resistor and compared against the internal 1.00V reference at RREF. This eliminates the need for optocouplers or third-winding sensing while maintaining ±5% typical output regulation accuracy.

What is the purpose of the TC pin on the LT8304HS8E-1#PBF?

The TC pin on the LT8304HS8E-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. By connecting an RTC resistor between TC and RREF, a PTAT current offsets V_F drift-enabling stable 3.3V or 5V outputs across –40°C to +150°C without external temperature sensors.

Is the LT8304HS8E-1#PBF pin-compatible with other variants in the LT8304 family?

Yes, the LT8304HS8E-1#PBF is fully pin-compatible with all LT8304 and LT8304-1 variants in the 8-lead SO package (S8E), including LT8304ES8E-1#PBF and LT8304IS8E-1#PBF. Differences are limited to temperature grade (H-grade = –40°C to +150°C), minor parameter tolerances, and marking-no PCB layout changes are required when upgrading from E/I to H grade.

What transformer turns ratio is recommended for a 5V output using the LT8304HS8E-1#PBF with 24V–72V input?

For a 5V output with 24V–72V input, a 6:1 primary-to-secondary turns ratio is recommended-as validated in the datasheet's typical application (TA01a). This ratio balances switch voltage stress (≤110V during off-time), efficiency (>85%), and output power capability (up to 4.2A at 72V_IN). The LT8304-1 variant's enhanced ringing immunity makes it especially robust with this high step-up ratio.