Analog Devices Inc. LTC3805IDD-5#TRPBF

Overview

LTC3805IDD-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 with only 360µA quiescent current. It is used in isolated auxiliary power supplies for telecom and automotive systems.

For engineers reviewing the LTC3805IDD-5#TRPBF datasheet, LTC3805IDD-5#TRPBF pinout, LTC3805IDD-5#TRPBF application, or LTC3805IDD-5#TRPBF equivalent, key selection considerations include its 10-lead 3mm × 3mm DFN package, 4.5V VCC turn-on threshold, 100mV current sense voltage, RUN pin with precision hysteresis, and compatibility with high-input-voltage biasing schemes using the internal 9.5V shunt regulator.

Technical Context

The LTC3805IDD-5#TRPBF implements peak-current-mode control with an error amplifier whose output (ITH pin) sets the current comparator trip threshold. Its oscillator frequency is set by an external resistor on the FS pin and can be synchronized to an external clock via the SYNC pin. Slope compensation is generated internally as a 10µA linear ramp injected at the ISENSE pin.

Overcurrent protection uses dual sensing: primary current limiting via ISENSE (with clamped 100mV threshold), and fault detection via OC pin (adjustable 85–115mV threshold). Soft-start and fault timeout are jointly managed by the SSFLT pin, where an external capacitor programs both ramp-up time and post-fault holdoff duration.

Key Specifications

Pinout & Package

The LTC3805IDD-5#TRPBF is housed in a 10-lead, 3mm × 3mm plastic DFN package with exposed thermal pad (Pin 11 = GND). The pad must be soldered to a PCB ground plane 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 DC/DC controller applications.

Compared with LTC3873EDD-5#TRPBF and LM5122MMX/NOPB, the LTC3805IDD-5#TRPBF uniquely balances programmable frequency, integrated slope compensation, and dual-mode soft-start/fault timeout in a thermally optimized DFN - making it optimal for space-constrained, multi-condition auxiliary supplies requiring design flexibility and robust fault recovery.

Availability

LTC3805IDD-5#TRPBF is available at Aetrix Electronics and suitable for automotive auxiliary power, telecom housekeeping supplies, and isolated sensor interfaces requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for LTC3805IDD-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, Inc. (ADI) is a global semiconductor leader specializing in high-performance analog, mixed-signal, and power management ICs, with deep expertise in precision control and energy-efficient power conversion.

The LTC3805 family was designed by Linear Technology (acquired by ADI in 2017) specifically for flexible, high-reliability DC/DC controller applications in isolated and non-isolated topologies - emphasizing low quiescent current, wide VIN bias capability, and robust fault management for mission-critical power rails.

FAQ

What is the maximum input voltage that can safely power the LTC3805IDD-5#TRPBF?

The LTC3805IDD-5#TRPBF does not have a hard maximum input voltage limit because its VCC pin includes an internal 9.5V shunt regulator. When powered via a resistor from a high-voltage source (e.g., 24V or 48V), the shunt regulates VCC to ~9.5V as long as sink current remains ≤25mA. Therefore, the practical upper limit depends on resistor selection and power dissipation - not the IC's absolute ratings. The LTC3805IDD-5#TRPBF itself draws only 360µA during operation, enabling efficient high-VIN biasing.

How does the LTC3805IDD-5#TRPBF implement slope compensation, and is an external component required?

The LTC3805IDD-5#TRPBF generates slope compensation internally via a 10µA linear current ramp injected at the ISENSE pin. This ramp begins at zero at 6% duty cycle and peaks at 80% duty cycle. An external resistor from ISENSE to ground converts this current into a voltage ramp that counteracts subharmonic oscillation. No external ramp generator is needed - only the resistor is required for designs operating above 50% duty cycle. The LTC3805IDD-5#TRPBF datasheet provides equations to calculate the optimal resistance value based on inductor value and switching frequency.

Can the LTC3805IDD-5#TRPBF be used in a synchronous rectification configuration?

The LTC3805IDD-5#TRPBF is a controller-only IC and does not integrate synchronous rectifier drivers. However, it is fully compatible with synchronous rectification when paired with external gate drivers or dedicated SR controllers. Its GATE output drives the primary-side N-channel MOSFET, while secondary-side synchronous FETs require separate timing - typically derived from the main transformer waveform or an auxiliary winding. The LTC3805IDD-5#TRPBF's precise current sensing and fast fault response make it well-suited for such configurations, especially in high-efficiency flyback or forward converters.

What is the function of the SSFLT pin on the LTC3805IDD-5#TRPBF, and how does it differ from a standard soft-start pin?

The SSFLT pin on the LTC3805IDD-5#TRPBF serves a dual purpose: it controls both soft-start ramp time and fault timeout duration. During startup, a capacitor from SSFLT to GND is charged by a 6µA current, delaying full regulation until the pin reaches ~2.25V. After an overcurrent fault, the same capacitor is discharged by a 2µA current; restart occurs when SSFLT falls to ~0.7V. This unified node eliminates the need for separate timing components - a key differentiator from conventional soft-start pins. The LTC3805IDD-5#TRPBF thus provides coordinated, capacitor-programmable recovery behavior critical for robust auxiliary supplies.

Does the LTC3805IDD-5#TRPBF support external clock synchronization, and what are the timing requirements?

Yes, the LTC3805IDD-5#TRPBF supports external clock synchronization via the SYNC pin. A rising edge on SYNC forces the beginning of a new switching cycle - i.e., the GATE pin goes high - regardless of the internal oscillator phase. The external clock frequency must be within 70kHz–700kHz, matching the LTC3805IDD-5#TRPBF's programmable range. Pulse width is flexible; minimum high time is not specified, but setup time relative to internal oscillator edge is negligible. This feature enables noise-sensitive systems (e.g., RF modules or audio circuits) to align switching edges and avoid beat frequencies. The LTC3805IDD-5#TRPBF maintains full current-mode control during synchronization.