Analog Devices Inc. LTC3805EDD-5#TRPBF

Overview

LTC3805EDD-5#TRPBF from Analog Devices (formerly Linear Technology) is a current-mode DC/DC controller IC designed to drive an external N-channel MOSFET in flyback, boost, and SEPIC topologies. It delivers ±1.5% output voltage accuracy, supports 70kHz–700kHz adjustable switching frequency via a single resistor, features programmable overcurrent protection with automatic restart, and operates from 4.7V–8.8V VCC or high-VIN bias through its internal 9.5V shunt regulator - enabling use in automotive auxiliary power supplies.

For engineers reviewing the LTC3805EDD-5#TRPBF datasheet, LTC3805EDD-5#TRPBF pinout, LTC3805EDD-5#TRPBF application, or LTC3805EDD-5#TRPBF equivalent, key selection considerations include its 10-lead 3mm × 3mm DFN package, 100mV current sense threshold, micropower 40µA startup current, RUN pin with precision hysteresis, and synchronous capability for noise-sensitive telecom and PoE systems.

Technical Context

The LTC3805EDD-5#TRPBF implements peak current-mode control using an internal error amplifier with transconductance of 333µA/V, a programmable oscillator with slope compensation injection (10µA ramp), and dual comparator architecture - one for current sensing (ITH-controlled trip) and another for overcurrent fault detection (OC pin). Its ITH pin serves as both loop compensation node and duty-cycle modulator, clamped between 0.7V and 1.9V.

It integrates undervoltage lockout on both VCC (4.5V turn-on, 4.0V turn-off) and RUN pins (1.207V ON / 1.170V OFF), supports external soft-start/fault timeout via SSFLT capacitor, and provides gate drive with 30ns rise/fall times into 3000pF. The device operates across –40°C to +85°C and uses an exposed-pad DFN for thermal management.

Key Specifications

Pinout & Package

The LTC3805EDD-5#TRPBF is housed in a 10-lead, 3mm × 3mm plastic DFN package with exposed pad (Pin 11) that must be soldered to PCB ground for electrical integrity and thermal performance (θ_JA = 45°C/W).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar current-mode flyback/boost controller applications.

Compared with LM5022MM/NOPB and UCC28083DR, the LTC3805EDD-5#TRPBF offers superior flexibility in frequency tuning, integrated high-VIN biasing, and robust fault management - making it optimal for compact, thermally constrained, or wide-input-range applications where reliability and design margin matter.

Availability

LTC3805EDD-5#TRPBF is available at Aetrix Electronics and suitable for automotive auxiliary power, telecom housekeeping supplies, and Power over Ethernet (PoE) powered devices requiring stable component supply, long-term lifecycle support, and consistent parametric performance across temperature.

Supply support for LTC3805EDD-5#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 acquired Linear Technology in 2017 and maintains full product support, documentation, and manufacturing continuity for all Linear DC/DC controller families.

The LTC3805EDD-5#TRPBF belongs to Linear's high-performance current-mode controller product line, engineered specifically for isolated and non-isolated step-up/step-down converters where precision regulation, low quiescent power, and robust fault handling are critical in automotive, telecom, and industrial power systems.

FAQ

What is the maximum allowable input voltage applied to the VCC pin of the LTC3805EDD-5#TRPBF?

The LTC3805EDD-5#TRPBF specifies an absolute maximum VCC-to-GND rating of –0.3V to 8.8V for low-impedance sources. However, when powered from high-VIN via a series resistor, the internal 9.5V shunt regulator clamps VCC - allowing safe operation with input voltages far exceeding 8.8V, provided the shunt current remains ≤25mA. This makes the LTC3805EDD-5#TRPBF suitable for 24V or 48V automotive and telecom biasing without external regulators.

Does the LTC3805EDD-5#TRPBF support synchronous rectification?

No, the LTC3805EDD-5#TRPBF does not support synchronous rectification. It is a controller-only IC that drives a single external N-channel MOSFET in flyback, boost, or SEPIC configurations. Synchronous rectification requires a second gate driver channel and timing control logic, which are not present in the LTC3805EDD-5#TRPBF. For synchronous designs, consider the LTC3873 or LTC3780 families instead.

Can the LTC3805EDD-5#TRPBF be used in a SEPIC converter, and what are the key layout considerations?

Yes, the LTC3805EDD-5#TRPBF is explicitly qualified for SEPIC operation per its datasheet. Key layout considerations include minimizing loop area of the coupled inductor/capacitor path, placing the ISENSE resistor close to the MOSFET source and GND, routing the SSFLT capacitor directly to the exposed pad, and ensuring the FB divider ground connects near the output capacitor negative terminal to avoid noise coupling. The 100mV current sense threshold helps reduce parasitic effects in high-current SEPIC paths.

How is the RUN pin hysteresis programmed on the LTC3805EDD-5#TRPBF?

The RUN pin hysteresis on the LTC3805EDD-5#TRPBF is partially built-in (35mV) and partially programmable. The device sources 5µA from the RUN pin when enabled, creating additional hysteresis dependent on the Thevenin resistance of the external voltage divider. To set falling threshold VIN(RUN,FALLING), select R1 and R2 such that R1 × 5µA contributes the desired offset - e.g., 100kΩ adds ~0.5V hysteresis. The LTC3805EDD-5#TRPBF datasheet provides exact formulas and example calculations in the Applications Information section.

What is the purpose of the SSFLT pin on the LTC3805EDD-5#TRPBF, and how does it affect fault recovery?

The SSFLT pin on the LTC3805EDD-5#TRPBF serves dual functions: it controls soft-start ramp rate during power-up and sets the fault timeout interval after overcurrent shutdown. During startup, a capacitor on SSFLT charges at 6µA until reaching ~2.25V, enabling closed-loop regulation. After an OC fault, the same capacitor discharges at 2µA from ~4.75V to ~0.7V; only then does the LTC3805EDD-5#TRPBF attempt automatic restart. This unified timing mechanism simplifies design while ensuring predictable recovery behavior.