Analog Devices Inc. LTC3900MPS8#TRPBF

Overview

LTC3900MPS8#TRPBF 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, pulse transformer synchronization, 4.5V–11V VCC supply range, and 15ns rise/fall times at 5V with 4700pF load. It enables high-efficiency 3.3V/40A telecom power supplies operating from 36V–72V input.

For engineers reviewing the LTC3900MPS8#TRPBF datasheet, LTC3900MPS8#TRPBF pinout, LTC3900MPS8#TRPBF application, or LTC3900MPS8#TRPBF equivalent, key selection criteria include its –55°C to 150°C extended temperature rating, differential current sense threshold (10.5mV typ.), SYNC input hysteresis (±0.2V), UVLO threshold (4.1V), and dual-driver timing precision for forward/catch MOSFET control in isolated DC/DC systems.

Technical Context

The LTC3900MPS8#TRPBF implements edge-sensitive dual-channel gate driving synchronized via external pulse transformer signals: negative SYNC edges activate FG (forward MOSFET) and deactivate CG (catch MOSFET), while positive edges do the inverse. Its internal timer resets on each SYNC negative transition and disables both drivers if SYNC is missing or malformed-preventing MOSFET latch-up during primary controller shutdown.

Current sensing uses a 250ns-delayed differential comparator monitoring CS+/CS– to detect reverse inductor current through Q4's R_DS(ON), with a 10.5mV threshold exhibiting +0.33%/°C TC matching typical MOSFET drift. The device integrates undervoltage lockout (4.1V trip, 0.5V hysteresis) and internal clamps (CS+ to 11V, TIMER to 0.5×VCC) for robust operation under transient conditions.

Key Specifications

Pinout & Package

Package: 8-lead plastic SO (SO-8), 150°C maximum junction temperature, –55°C to 150°C operating range.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LM5113SDX/NOPB and UCC27211D, the LTC3900MPS8#TRPBF uniquely integrates pulse-transformer synchronization, reverse-current detection, and programmable timeout in a single SO-8 package rated for –55°C to 150°C-making it the only drop-in solution for isolated forward converters requiring guaranteed fault-safe shutdown without external components.

Availability

LTC3900MPS8#TRPBF is available at Aetrix Electronics and suitable for 48V telecom power supplies, industrial control system PSUs, automotive heavy equipment power modules, and high-voltage distributed power systems requiring stable component supply across extended temperature ranges.

Supply support for LTC3900MPS8#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) is a global leader in high-performance analog, mixed-signal, and power management semiconductors.

The LTC3900 product line was designed specifically for isolated forward converter secondary-side synchronous rectification, emphasizing robustness, integrated protection, and seamless pulse-transformer interface compatibility in harsh thermal environments.

FAQ

What is the operating temperature range of the LTC3900MPS8#TRPBF?

The LTC3900MPS8#TRPBF is specified for operation from –55°C to 150°C junction temperature, making it suitable for military, aerospace, and extreme industrial applications. This extended range is achieved through rigorous testing and qualification per MIL-STD-883 methods, distinguishing it from commercial-grade variants like the LTC3900ES8#TRPBF (–40°C to 125°C). The LTC3900MPS8#TRPBF maintains full parameter compliance-including current sense threshold, propagation delay, and driver strength-across this entire range.

How does the LTC3900MPS8#TRPBF protect against reverse inductor current?

The LTC3900MPS8#TRPBF protects against reverse inductor current using a differential current sense comparator monitoring CS+ and CS– pins. When the inductor current reverses and flows into the catch MOSFET (Q4), causing CS+ to exceed CS– by more than 10.5mV, the LTC3900MPS8#TRPBF immediately pulls CG low. This action disables Q4 before avalanche occurs. The comparator activates 250ns after CG goes high to avoid turn-on ringing, and its 10.5mV threshold has a +0.33%/°C temperature coefficient matched to typical MOSFET R_DS(ON) drift.

Can the LTC3900MPS8#TRPBF be used with non-pulse-transformer SYNC sources?

Yes, the LTC3900MPS8#TRPBF can accept direct bipolar square-wave SYNC signals instead of pulse transformer coupling, provided the signal meets amplitude (±5V recommended), width (>75ns), and slew rate requirements. Figure 8 in the datasheet shows a symmetrical drive circuit using 74HC14/132 gates. However, galvanic isolation must be maintained externally-e.g., using digital isolators-since the LTC3900MPS8#TRPBF itself provides no internal isolation. Pulse transformer remains the preferred method for high-noise, high-CMTI environments like telecom and industrial systems.

What is the purpose of the TIMER pin on the LTC3900MPS8#TRPBF?

The TIMER pin on the LTC3900MPS8#TRPBF connects to an external RC network (RTMR/CTMR) to program a timeout period that disables both FG and CG outputs if the SYNC signal is missing or malformed. Each negative SYNC edge generates a 200ns reset pulse; if no valid edge occurs, the TIMER voltage rises until reaching 0.2×VCC, triggering shutdown. This prevents latch-up during primary controller faults or power-down sequences. Timeout duration is calculated as 0.2 × RTMR × CTMR + 0.27µs and is independent of VCC variation.

Does the LTC3900MPS8#TRPBF require external components for basic operation?

Yes, the LTC3900MPS8#TRPBF requires several external components for reliable operation: a 4.7µF ceramic capacitor from VCC to GND, an RC network (RTMR/CTMR) on the TIMER pin for timeout programming, series resistors (RCS1/RCS2/RCS3) on CS+/CS– for current sense scaling and clamp protection, and a pulse transformer (e.g., Coilcraft Q4470B) or isolated SYNC source. These are not optional-they enable core functions including UVLO bypass, fault timeout, reverse-current detection, and synchronization. No internal regulators or passive components are integrated beyond the driver stages and protection comparators.