Analog Devices Inc. LTC3900MPS8#PBF

Overview

LTC3900MPS8#PBF 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 and reverse inductor current detection, and operates across a 4.5V–11V VCC range with 15ns rise/fall times at 5V/4700pF - enabling high-efficiency 3.3V/40A telecom and industrial DC/DC conversion.

For engineers reviewing the LTC3900MPS8#PBF datasheet, LTC3900MPS8#PBF pinout, LTC3900MPS8#PBF application, or LTC3900MPS8#PBF equivalent, key selection criteria include its –55°C to 150°C extended temperature grade, differential current sense threshold (10.5mV typ.), SYNC input polarity sensitivity (±1.4V thresholds), and SO-8 package compatibility with high-voltage isolation barrier layouts.

Technical Context

The LTC3900MPS8#PBF implements dual-edge-triggered driver logic synchronized via an external pulse transformer: a negative SYNC edge forces FG high/CG low; a positive edge forces FG low/CG high. Its internal timer resets on every negative SYNC transition and disables both drivers if the timeout threshold (0.2 × VCC) is exceeded due to missing or malformed SYNC pulses.

Protection is implemented through three independent circuits: (1) undervoltage lockout (4.1V rising, 0.5V hysteresis), (2) differential current sense comparator active 250ns after CG turn-on (10.5mV threshold with +0.33%/°C TC matching MOSFET R_DS(ON)), and (3) internal clamp on CS+ (11V) and TIMER (0.5 × VCC) pins to limit transient stress during power-up/down.

Key Specifications

Pinout & Package

Package: 8-Lead Plastic Small Outline (SO-8), RoHS-compliant, lead-free finish. Pin 1 marked with dot; exposed pad not electrically connected.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LM5122MHE/NOPB and UCC24612DR, the LTC3900MPS8#PBF uniquely combines pulse-transformer synchronization, differential reverse-current detection, and VCC-independent timeout in a single SO-8 package - making it the only qualified solution for high-reliability isolated forward converters operating across –55°C to 150°C.

Availability

LTC3900MPS8#PBF is available at Aetrix Electronics and suitable for 48V telecom power supplies, high-voltage distributed power step-down systems, and automotive/industrial control power supplies requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for LTC3900MPS8#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 full product support, datasheet documentation, and application engineering for legacy Linear parts including the LTC3900 family.

The LTC3900 product line was designed specifically for high-efficiency, isolated forward converter topologies requiring robust secondary-side synchronous rectification with fail-safe protection - targeting telecom, industrial, and automotive power systems.

FAQ

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

The LTC3900MPS8#PBF is fully tested and guaranteed over –55°C to 150°C junction temperature. This MP-grade specification exceeds commercial and industrial grades, making it suitable for aerospace, military, and under-hood automotive applications where extreme thermal margins are required. The device incorporates internal thermal compensation for current sense and timing functions across this full range.

How does the LTC3900MPS8#PBF detect reverse inductor current?

The LTC3900MPS8#PBF detects reverse inductor current by monitoring the voltage across the drain-source terminals of the catch MOSFET (Q4) via its differential CS+ and CS– inputs. When CS+ rises above CS– by more than 10.5mV - indicating reverse current flow - the LTC3900MPS8#PBF pulls CG low within nanoseconds. This comparator activates 250ns after CG goes high to avoid switching noise.

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

Yes - the LTC3900MPS8#PBF accepts bipolar square-wave SYNC signals directly, provided positive and negative amplitudes exceed ±1.4V (with ±0.2V hysteresis). Figure 8 shows a symmetrical drive circuit using 74HC14/132 gates. For lowest propagation delay, amplitudes >±5V are recommended. Direct connection avoids transformer losses but requires careful isolation design.

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

The TIMER pin on the LTC3900MPS8#PBF accepts an external RC network (RTMR/CTMR) to program a timeout period. The internal timer resets on every negative SYNC edge; if SYNC is missing or malformed, the timer charges until reaching 0.2×VCC, then disables both FG and CG outputs. This prevents MOSFET latch-up and avalanche during power-down or controller faults.

Does the LTC3900MPS8#PBF require external gate resistors for MOSFET driving?

No - the LTC3900MPS8#PBF integrates low-impedance drivers (RONH/RONL ≈ 1.2Ω typ.) capable of delivering >1A peak current, eliminating need for external gate resistors in most designs. However, small series resistors (≤5Ω) may be added to damp ringing in high-dV/dt environments. Layout best practice emphasizes short, low-inductance gate traces to MOSFETs.