Analog Devices Inc. LTC3805IMSE-5#PBF

Overview

LTC3805IMSE-5#PBF 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 features programmable switching frequency (70–700 kHz), ±1.5% reference accuracy, 100 mV current sense threshold, 4.5 V undervoltage lockout, and operates across –40°C to +125°C. It enables compact, isolated auxiliary power supplies in telecom and automotive systems.

For engineers reviewing the LTC3805IMSE-5#PBF datasheet, LTC3805IMSE-5#PBF pinout, LTC3805IMSE-5#PBF application, or LTC3805IMSE-5#PBF equivalent, key selection criteria include its adjustable slope compensation, micropower startup (40 µA), RUN pin with precision hysteresis, soft-start programmability via SSFLT capacitor, and compatibility with high-VIN biasing schemes using its internal 9.5 V shunt regulator.

Technical Context

The LTC3805IMSE-5#PBF implements peak current-mode control with an error amplifier feeding the ITH node to set the current comparator threshold. Its oscillator frequency is set by a single resistor on the FS pin and supports synchronization via the SYNC input. Slope compensation is generated internally as a 10 µA linear ramp injected at the ISENSE pin.

Overcurrent protection uses dual sensing: primary current limiting via ISENSE (100 mV threshold) and fault-level detection via OC pin (also 100 mV nominal), with automatic restart after timeout. The RUN pin provides precision enable/disable control with 35 mV built-in hysteresis plus user-programmable hysteresis via external divider current sourcing.

Key Specifications

Pinout & Package

The LTC3805IMSE-5#PBF is housed in a 10-lead MSOP package with exposed pad (Pin 11) that must be soldered to PCB ground for thermal and electrical performance.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LTC3873EMSE-5#PBF and UCC28C43DR, the LTC3805IMSE-5#PBF uniquely combines programmable frequency, micropower startup, integrated VCC shunt regulation, and dual overcurrent protection-making it optimal for compact, wide-input, isolated auxiliary supplies requiring design flexibility and robust fault handling.

Availability

LTC3805IMSE-5#PBF is available at Aetrix Electronics and suitable for automotive power supplies, telecom power supplies, and isolated electronic equipment requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for LTC3805IMSE-5#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, documentation, and manufacturing continuity for all Linear power management ICs.

The LTC3805-5 belongs to Linear's high-performance current-mode controller family, engineered specifically for isolated and non-isolated DC/DC converters demanding precision regulation, wide input range operation, and robust fault management in harsh environments.

FAQ

What is the maximum allowable input voltage applied to the VCC pin of the LTC3805IMSE-5#PBF?

The LTC3805IMSE-5#PBF specifies an absolute maximum VCC-to-GND rating of –0.3 V to 8.8 V for low-impedance sources. However, its internal 9.5 V shunt regulator allows safe operation when powered from higher voltages (e.g., 24 V or 48 V) via a series current-limiting resistor, provided the shunt does not sink more than 25 mA. This makes the LTC3805IMSE-5#PBF suitable for direct high-VIN biasing without external regulators.

Does the LTC3805IMSE-5#PBF support synchronous rectification?

No, the LTC3805IMSE-5#PBF does not support synchronous rectification. It drives only a single external N-channel MOSFET in the high-side switch position and relies on external diodes (e.g., Schottky or fast recovery) for rectification in flyback, boost, or SEPIC configurations. Synchronous rectifier control signals are not provided; designers must implement separate gate drive logic if synchronous rectification is required.

How is the soft-start time programmed on the LTC3805IMSE-5#PBF?

The soft-start time on the LTC3805IMSE-5#PBF is programmed using an external capacitor (CSS) connected from the SSFLT pin (Pin 1) to GND. During startup, CSS is charged with a 6 µA internal current. Soft-start completes when SSFLT reaches ~2.25 V, resulting in a time constant tSS ≈ CSS × 2.25 V / 6 µA. For example, a 100 nF capacitor yields ~38 ms soft-start. The same capacitor also sets fault timeout duration via 2 µA discharge.

Can the LTC3805IMSE-5#PBF operate in discontinuous conduction mode (DCM)?

Yes, the LTC3805IMSE-5#PBF inherently supports DCM operation. As a current-mode controller, it regulates based on peak inductor current. When load current drops sufficiently, the controller naturally reduces duty cycle until the inductor current falls to zero each cycle - entering DCM. No additional configuration is needed; DCM behavior emerges automatically under light loads and is confirmed in typical application waveforms in the datasheet.

What is the purpose of the exposed pad (Pin 11) on the LTC3805IMSE-5#PBF MSOP package?

The exposed pad (Pin 11) on the LTC3805IMSE-5#PBF MSOP package serves as the primary thermal and electrical ground connection. It must be soldered to a PCB copper pour tied to system ground to achieve rated thermal performance (θJA = 45°C/W) and ensure stable operation. Leaving it unconnected degrades thermal dissipation, increases junction temperature, and may cause premature device failure or parameter drift - especially under sustained high-duty-cycle operation.