Analog Devices Inc. LT3640IUFD#TRPBF

Overview

LT3640IUFD#TRPBF from Analog Devices (formerly Linear Technology) is a dual-channel monolithic buck switching regulator IC with integrated power-on reset and window-mode watchdog timer. It delivers 1.3A from its high-voltage nonsynchronous channel (4V–35V input, 3.3V/0.8A typical output) and 1.1A from its low-voltage synchronous channel (2.5V–5.5V input, 1.8V/0.8A typical output), operating at adjustable 350kHz–2.5MHz frequency. It is used in automotive ECU power rails requiring fault-tolerant sequencing and supervision.

For engineers reviewing the LT3640IUFD#TRPBF datasheet, LT3640IUFD#TRPBF pinout, LT3640IUFD#TRPBF application, or LT3640IUFD#TRPBF equivalent, key selection criteria include dual-output voltage tracking capability, programmable reset/watchdog timing via external capacitors, cycle-by-cycle current limiting on both channels, Burst Mode® operation for light-load efficiency, and thermal performance in the 4mm × 5mm QFN package with exposed pad.

Technical Context

The LT3640IUFD#TRPBF integrates two independent current-mode buck regulators sharing a single adjustable oscillator. The high-voltage channel uses an internal 2.4A NPN switch with 36.5V OVLO and supports up to 55V transient tolerance; the low-voltage channel employs internal synchronous MOSFETs with PMOS/NMOS R_DS(ON) of 275mΩ/200mΩ and operates down to 2.3V input. Both channels feature soft-start via SS1/SS2 pins and cycle-by-cycle current limit with foldback below 0.2V FB1.

Its supervision functions include a dual-channel power-on reset (RST1/RST2, timeout set by CPOR capacitor) and a windowed watchdog timer (WDO, boundaries set by CWDT capacitor) that monitors WDI pulse timing. The device enters low-ripple Burst Mode® below ~100mA load to maintain 290µA typical quiescent current while sustaining regulation.

Key Specifications

Pinout & Package

The LT3640IUFD#TRPBF is housed in a thermally enhanced 28-pin (4mm × 5mm) plastic QFN package with exposed pad (Pin 29) soldered to PCB ground for θ_JA = 34°C/W and θ_JC = 2.7°C/W.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar dual-buck regulator with supervision applications.

Compared with LT3640IUFD#TRPBF, LT3641IUFD#TRPBF offers higher HV current and input range while maintaining full pin compatibility and supervision features, whereas TPS65217CRSLR provides broader power integration but sacrifices programmable timing and automotive-grade supervision.

Availability

LT3640IUFD#TRPBF is available at Aetrix Electronics and suitable for automotive electronic control units, industrial PLC I/O modules, medical patient monitors, and telecom remote radio units requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for LT3640IUFD#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 technical and manufacturing continuity for the LT® product family, known for high-performance analog and power management ICs.

The LT3640IUFD#TRPBF belongs to Linear's monolithic switching regulator product line, designed specifically for space-constrained, safety-critical applications requiring dual regulated outputs with integrated system supervision and robust fault protection.

FAQ

What is the maximum input voltage the LT3640IUFD#TRPBF can withstand without damage?

The LT3640IUFD#TRPBF has an absolute maximum VIN rating of 55V for non-repetitive 1-second transients. Its overvoltage lockout (OVLO) activates at 36.5V typical, disabling switching to protect internal circuitry. Continuous operation is rated up to 35V. This makes the LT3640IUFD#TRPBF suitable for automotive battery inputs subject to load dump events, provided external TVS clamping is used for sustained >35V conditions.

How does the LT3640IUFD#TRPBF implement windowed watchdog functionality?

The LT3640IUFD#TRPBF implements windowed watchdog using the WDI, WDE, and CWDT pins. When WDE is asserted, the device monitors falling edges on WDI. If consecutive edges occur faster than t_WDL (e.g., 2ms with 820pF) or slower than t_WDU (e.g., 32ms), WDO is pulled low. The LT3640IUFD#TRPBF requires no external logic to detect both µP lockup and runaway conditions - a key differentiator from basic timeout watchdogs.

Can the LT3640IUFD#TRPBF operate with only the low-voltage channel enabled?

Yes, the LT3640IUFD#TRPBF can operate with only the low-voltage channel active. EN2 must be pulled high (>1.5V), VIN2 must exceed 2.3V, and FB1 must be above 1.165V (to satisfy the interlock condition). The HV channel remains disabled if EN/UVLO is held low or VIN is below 3.6V. This mode allows standalone 1.8V/1.1A regulation from a clean 3.3V source, with full access to RST2, PGOOD, and soft-start via SS2.

What thermal performance can be expected from the LT3640IUFD#TRPBF in its QFN package?

The LT3640IUFD#TRPBF in the 4mm × 5mm QFN package achieves θ_JC = 2.7°C/W and θ_JA = 34°C/W with proper PCB layout: the exposed pad (Pin 29) must be soldered to a ≥4cm² copper pour with ≥4 thermal vias. At 1.3A/1.1A continuous load and 25°C ambient, junction temperature rise is typically <45°C - well within the –40°C to +125°C operating range. Derating curves in the datasheet confirm full output current up to +105°C ambient.

Does the LT3640IUFD#TRPBF require external catch diodes for the high-voltage channel?

Yes, the LT3640IUFD#TRPBF high-voltage channel is nonsynchronous and requires an external Schottky catch diode connected between SW1 and GND. The DA pin senses diode anode current for valley current limiting. No external diode is needed for the low-voltage channel, as it uses internal synchronous MOSFETs. Diode selection must consider reverse voltage rating (>VIN), forward voltage (<0.5V), and thermal dissipation - typical parts include MBR0530 or SBM-20H30.