Analog Devices Inc. LTC3900ES8#TRPBF

Overview

LTC3900ES8#TRPBF from Analog Devices (formerly Linear Technology) is a secondary-side N-channel synchronous rectifier driver for isolated forward converter power supplies. It drives two external MOSFETs (forward and catch), accepts pulse-transformer synchronization, features programmable timeout protection, reverse inductor current detection (10.5 mV threshold), and operates from 4.5 V to 11 V VCC - enabling high-efficiency 3.3 V/40 A telecom DC/DC conversion.

For engineers reviewing the LTC3900ES8#TRPBF datasheet, LTC3900ES8#TRPBF pinout, LTC3900ES8#TRPBF application, or LTC3900ES8#TRPBF equivalent, key selection criteria include SYNC edge sensitivity (±1.4 V thresholds), 15 ns rise/fall time at 5 V with 4700 pF load, undervoltage lockout (4.1 V), differential current sense input, and SO-8 thermal performance (θ_JA = 130°C/W).

Technical Context

The LTC3900ES8#TRPBF implements dual-edge–sensitive synchronization logic using separate positive and negative comparators (S+ and S−) with ±1.4 V thresholds and 0.2 V hysteresis. Its timer circuit resets on every SYNC negative transition and times out if SYNC pulses are missing or missequenced - disabling both drivers when TIMER exceeds 0.2 × V_CC.

Current sensing activates 250 ns after CG goes high and compares CS+–CS− voltage against a temperature-compensated 10.5 mV threshold (0.33%/°C TC) to detect reverse inductor current. The driver outputs feature matched pull-up/pull-down resistances (0.9–2.0 Ω) and deliver 2 A peak current for fast MOSFET switching.

Key Specifications

Pinout & Package

Package: 8-lead plastic SO (SO-8), 130°C/W junction-to-ambient thermal resistance, –40°C to 125°C operating junction temperature.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar synchronous rectifier driver applications.

Compared with LM5109BMM/NOPB and UCC27211D, the LTC3900ES8#TRPBF integrates forward-converter–specific functions - including dual-edge SYNC decoding, reverse-current detection, and programmable timeout - eliminating ≥4 external components and ensuring safe operation during primary-side fault conditions without redesign.

Availability

LTC3900ES8#TRPBF is available at Aetrix Electronics and suitable for 48 V telecom power supplies, industrial isolated DC/DC converters, and automotive heavy equipment PSUs requiring stable component supply, extended temperature support (–40°C to 125°C), and long-term production continuity.

Supply support for LTC3900ES8#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, Inc. (acquired Linear Technology in 2017) designs high-performance analog, mixed-signal, and power management ICs for precision, reliability, and rugged operation.

The LTC3900 product line delivers isolated secondary-side synchronous rectifier drivers optimized for forward converter topologies - addressing efficiency, safety, and timing-critical requirements in telecom, industrial, and transportation power systems.

FAQ

What is the primary function of the LTC3900ES8#TRPBF in a forward converter?

The LTC3900ES8#TRPBF serves as a secondary-side synchronous rectifier driver that replaces Schottky diodes with N-channel MOSFETs (Q3 and Q4) in isolated forward converters. It receives synchronization signals via a pulse transformer, alternately drives the forward and catch MOSFETs, and incorporates protection features including reverse current detection and programmable timeout. This functionality is integral to the LTC3900ES8#TRPBF's role in achieving >92 % efficiency in 48 V telecom power supplies.

How does the LTC3900ES8#TRPBF protect against reverse inductor current?

The LTC3900ES8#TRPBF monitors the voltage across the catch MOSFET's drain-source terminals using its differential CS+ and CS– inputs. When the inductor current reverses and causes CS+ to exceed CS– by more than 10.5 mV, the LTC3900ES8#TRPBF immediately pulls the CG output low to turn off the catch MOSFET. This action prevents avalanche breakdown and potential MOSFET damage during power-down or light-load discontinuous conduction mode.

Can the LTC3900ES8#TRPBF operate with a 3.3 V VCC supply?

No, the LTC3900ES8#TRPBF requires a minimum VCC supply of 4.5 V and operates up to 11 V. Its undervoltage lockout activates below 4.1 V, and the device remains disabled until VCC rises above 4.5 V. A 3.3 V rail cannot power the LTC3900ES8#TRPBF directly; a dedicated bias supply - such as a peak-detected winding from the main transformer - must be used to generate ≥4.5 V for reliable LTC3900ES8#TRPBF operation.

What is the purpose of the TIMER pin on the LTC3900ES8#TRPBF?

The TIMER pin on the LTC3900ES8#TRPBF connects to an external RC network (R_TMR/C_TMR) to set a programmable timeout period. The internal timer resets on every negative edge of the SYNC signal. If SYNC pulses are missing, incorrect, or missequenced, the TIMER voltage rises until it reaches 0.2 × V_CC, at which point both driver outputs (FG and CG) are disabled. This protects external MOSFETs from uncontrolled conduction during primary-side controller faults - a core safety function of the LTC3900ES8#TRPBF.

Does the LTC3900ES8#TRPBF support direct logic-level SYNC input without a pulse transformer?

Yes, the LTC3900ES8#TRPBF SYNC input accepts direct bipolar square-wave signals - not just pulse-transformer–coupled waveforms. Its ±1.4 V thresholds and ±12 V absolute maximum rating allow connection to logic gates (e.g., 74HC14) or microcontroller outputs, provided the signal swings sufficiently beyond the thresholds to ensure clean edge detection. However, galvanic isolation is lost without a pulse transformer, so this configuration is only suitable for non-isolated or internally referenced forward converter implementations using the LTC3900ES8#TRPBF.