Analog Devices Inc. LT3689IMSE-5#TRPBF

Overview

LT3689IMSE-5#TRPBF from Analog Devices (formerly Linear Technology) is a 700mA monolithic step-down switching regulator with integrated power-on reset (POR) and pin-selectable watchdog timer (window or timeout mode), operating from 3.6V to 36V input, delivering fixed 5V output with ±1% accuracy over temperature, 85µA quiescent current in Burst Mode®, and robust 60V transient tolerance. It serves as a system-supervisory power solution in automotive ECU and industrial control applications requiring reliable microprocessor reset and fault detection.

For engineers reviewing the LT3689IMSE-5#TRPBF datasheet, LT3689IMSE-5#TRPBF pinout, LT3689IMSE-5#TRPBF application, or LT3689IMSE-5#TRPBF equivalent, key selection considerations include its fixed 5V output, programmable POR delay via CPOR capacitor, independent watchdog timing via CWDT, 16-pin MSOP package with exposed thermal pad, and compatibility with external catch diodes for high-voltage transient resilience.

Technical Context

The LT3689IMSE-5#TRPBF implements constant-frequency current-mode PWM control with frequency programmability (350kHz–2.2MHz via RT resistor) and automatic transition to low-ripple Burst Mode® at light loads. Its internal bipolar NPN switch, BST-boosted gate drive, and DA-pin current monitoring enable stable operation up to 36V continuous input and safe clamping during 60V transients.

Supervisory functions are hardware-decoupled: the POR comparator asserts RST low when VOUT falls below 90% of 5V (i.e., 4.5V), with delay set by CPOR capacitance (2.3ms/nF); the watchdog operates independently via WDI input and W/T pin configuration, with upper/lower boundaries (tWDU/tWDL) determined by CWDT capacitance per tWDU = 18.2·CWDT and tWDL = 0.588·CWDT (CWDT in nF, results in ms/µs).

Key Specifications

Pinout & Package

LT3689IMSE-5#TRPBF uses a 16-lead plastic MSOP package with exposed thermal pad (Pin 17 = GND), θJA = 43°C/W, requiring soldering of the exposed pad to PCB ground plane for thermal and electrical integrity.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar step-down regulator with supervisory functions applications.

Compared with LTC3637EMSE#TRPBF and MAX20004AATP/V+T, the LT3689IMSE-5#TRPBF uniquely combines 60V transient tolerance, DA-pin diode-current fault protection, and fully independent capacitor-programmable POR/watchdog timing - making it optimal for high-reliability automotive and industrial systems where fault coverage and surge resilience are non-negotiable.

Availability

LT3689IMSE-5#TRPBF is available at Aetrix Electronics and suitable for automotive electronic control units, industrial programmable logic controllers, and medical diagnostic subsystems requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for LT3689IMSE-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. (acquired Linear Technology in 2017) is a global leader in high-performance analog, mixed-signal, and power management semiconductors, serving precision instrumentation, industrial automation, and automotive markets.

The LT3689 product line was designed specifically for automotive and industrial applications demanding integrated power regulation plus deterministic microprocessor supervision - combining robust DC/DC conversion with hardware-enforced system-level safety functions.

FAQ

What is the guaranteed operating temperature range for the LT3689IMSE-5#TRPBF?

The LT3689IMSE-5#TRPBF is guaranteed to operate over a junction temperature range of –40°C to 125°C. This "I" grade rating is validated across all electrical specifications in the datasheet, including output voltage accuracy, reset threshold, and watchdog timing, making it suitable for under-hood automotive and industrial environments where ambient temperatures exceed 85°C.

Does the LT3689IMSE-5#TRPBF require an external catch diode, and what are the key selection criteria?

Yes, the LT3689IMSE-5#TRPBF requires an external Schottky catch diode connected between SW and GND. Key selection criteria include: 40V+ reverse voltage rating (to handle 60V transients), low forward voltage (<0.5V at 1A), fast recovery (<50ns), and thermal capability matching the 700mA peak inductor current. Diodes such as Diodes Inc. B140HB or Vishay VSKY120 are validated in typical applications.

How is the power-on reset timeout period set for the LT3689IMSE-5#TRPBF?

The power-on reset timeout period for the LT3689IMSE-5#TRPBF is set by an external capacitor (CPOR) connected between Pin 3 (CPOR) and GND. The relationship is linear: tRST = 2.3ms per nanofarad. For example, an 8.2nF capacitor yields a nominal 18.9ms reset delay, which is confirmed across temperature in the datasheet's Figure G33.

Can the LT3689IMSE-5#TRPBF be synchronized to an external clock, and what are the constraints?

Yes, the LT3689IMSE-5#TRPBF supports external synchronization via the SYNC pin (Pin 5). The applied clock must have positive and negative pulse widths ≥80ns. Critically, the internal RT-set switching frequency must be at least 20% lower than the lowest expected synchronization frequency to avoid instability or loss of lock - e.g., for a 1MHz sync signal, RT must be configured for ≤800kHz.

What happens to the LT3689IMSE-5#TRPBF during a 60V input transient, and how does it recover?

During a 60V input transient, the LT3689IMSE-5#TRPBF disables switching when VIN exceeds 38V (typical OVLO threshold), allowing the output to fall. The internal circuitry remains powered and functional, and RST asserts low when VOUT drops below 4.5V. Once VIN returns below 36V, the part automatically resumes regulation without latch-up or manual reset - verified in transient immunity testing per datasheet Figure G20.