Analog Devices Inc. LTC3900ES8#PBF

Overview

LTC3900ES8#PBF from Analog Devices (formerly Linear Technology) is a secondary-side N-channel synchronous rectifier driver for isolated forward converters, featuring programmable timeout protection, reverse inductor current detection via R_DS(ON)-based sensing, and pulse transformer synchronization. It operates with 4.5V–11V V_CC, delivers 15ns rise/fall times at 5V/4700pF, and includes undervoltage lockout at 4.1V. It enables high-efficiency 3.3V/40A telecom power supplies.

For engineers reviewing the LTC3900ES8#PBF datasheet, LTC3900ES8#PBF pinout, LTC3900ES8#PBF application, or LTC3900ES8#PBF equivalent, key selection criteria include its SO-8 package compatibility, ±1.4V SYNC threshold with hysteresis, 10.5mV current sense threshold (with +0.33%/°C TC), dual gate drive capability (FG/CG), and integrated reverse-current shutdown timing.

Technical Context

The LTC3900ES8#PBF implements edge-triggered, polarity-sensitive SYNC input logic with separate S+ and S− comparators to decode alternating positive/negative pulses from a pulse transformer. Its timer circuit uses an external RC network (RTMR/CTMR) referenced to 0.2×V_CC to generate a programmable timeout-reset on every negative SYNC edge and disabled if sequential negatives occur without intervening positives.

Current sensing is differential (CS+/CS−), active only 250ns after CG goes high, with a 10.5mV threshold that tracks MOSFET R_DS(ON) temperature coefficient. Driver outputs feature matched pull-up/pull-down resistances (0.9–2.0Ω) and support peak currents up to 2A, enabling fast switching of low-R_DS(ON) N-channel MOSFETs in high-frequency forward topologies.

Key Specifications

Pinout & Package

Package: 8-Lead Plastic Small Outline (SO-8), RoHS-compliant, –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 UCC24612DR, the LTC3900ES8#PBF uniquely combines transformer-synchronized dual-N-channel drive, R_DS(ON)-tracking current sense, and RC-programmable timeout-making it the only option qualified for high-reliability, high-current (>30A), isolated forward converters requiring deterministic fault response without MCU intervention.

Availability

LTC3900ES8#PBF is available at Aetrix Electronics and suitable for 48V telecom power supplies, industrial control system power modules, and high-voltage distributed power step-down converters requiring stable component supply and long-term lifecycle assurance.

Supply support for LTC3900ES8#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, Inc. (acquired Linear Technology in 2017) is a global leader in high-performance analog, mixed-signal, and power management semiconductors.

The LTC3900 product line was designed specifically for secondary-side synchronous rectification in isolated forward converters, emphasizing robust pulse transformer interface, MOSFET R_DS(ON)-compensated current sensing, and autonomous fault protection without host controller dependency.

FAQ

What is the function of the TIMER pin on the LTC3900ES8#PBF?

The TIMER pin on the LTC3900ES8#PBF accepts an external RC network (RTMR/CTMR) to set a programmable timeout period. The internal timer resets on every negative SYNC edge; if SYNC stops or becomes invalid, the timer charges until reaching 0.2×V_CC, then forces both FG and CG low to disable the MOSFETs. This prevents latch-up during primary controller faults or power-down sequences.

How does the LTC3900ES8#PBF detect reverse inductor current?

The LTC3900ES8#PBF detects reverse inductor current by monitoring the voltage across the drain-to-source terminals of the catch MOSFET (Q4) via the CS+ and CS− pins. When CS+ rises >10.5mV above CS−-indicating reverse current flow-the device pulls CG low within nanoseconds. This comparator activates 250ns after CG goes high to avoid turn-on ringing artifacts.

Can the LTC3900ES8#PBF drive both high-side and low-side N-channel MOSFETs simultaneously?

No-the LTC3900ES8#PBF drives two N-channel MOSFETs in complementary mode: FG controls the forward MOSFET (Q3) and CG controls the catch MOSFET (Q4). Their states are strictly anti-phase and determined solely by SYNC polarity-negative SYNC asserts FG/high and CG/low; positive SYNC asserts FG/low and CG/high. Simultaneous conduction is prevented by design.

What is the purpose of the SYNC input's ±1.4V thresholds on the LTC3900ES8#PBF?

The ±1.4V thresholds on the LTC3900ES8#PBF SYNC input enable reliable edge detection of bipolar pulses from a pulse transformer, even with amplitude variation or noise. The 0.2V hysteresis on each threshold prevents chatter during slow or noisy transitions. This dual-threshold architecture allows unambiguous decoding of alternating positive/negative SYNC edges to sequence FG and CG drive states correctly.

Does the LTC3900ES8#PBF require external components for basic operation?

Yes-the LTC3900ES8#PBF requires several external components for functional operation: a 4.7µF ceramic capacitor on V_CC-to-GND, an RC network (RTMR/CTMR) on the TIMER pin for timeout programming, series resistors (RCS1/RCS2/RCS3) on CS+ and CS− for current sense scaling and clamp protection, and a pulse transformer with appropriate CSG/RSYNC values on SYNC to ensure proper pulse amplitude and width.