Analog Devices Inc. LT3689IUD-5#TRPBF

Overview

LT3689IUD-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, and featuring 85µA quiescent current in Burst Mode® at 12V_IN–3.3V_OUT. It is used in automotive ECU power rails requiring fault-tolerant supervision.

For engineers reviewing the LT3689IUD-5#TRPBF datasheet, LT3689IUD-5#TRPBF pinout, LT3689IUD-5#TRPBF application, or LT3689IUD-5#TRPBF equivalent, key selection criteria include its programmable POR delay (via CPOR capacitor), independently adjustable watchdog upper/lower boundaries (via CWDT), 350kHz–2.2MHz synchronizable switching frequency, internal 700mA NPN switch, and 60V transient survivability - all in a thermally enhanced 3mm × 3mm QFN package.

Technical Context

The LT3689IUD-5#TRPBF implements constant-frequency current-mode PWM control with slope compensation and frequency foldback during overload. Its internal 0.8V reference regulates feedback via a fixed resistor divider for 5V output, while the EN/UVLO pin provides programmable undervoltage lockout with hysteresis (1.26V threshold, 4.3µA hysteresis current).

Its supervisory functions are hardware-decoupled: the POR comparator monitors V_OUT against 90% of regulation (4.5V for 5V output), asserting RST low for t_RST = 2.3ms/nF after crossing threshold; the watchdog uses WDI edge detection and W/T pin logic to select window mode (dual-boundary timing) or timeout mode (single upper-boundary), both set by CWDT capacitance per t_WDU = 18.2·C_WDT (ms) and t_WDL = 0.588·C_WDT (ms).

Key Specifications

Pinout & Package

LT3689IUD-5#TRPBF is housed in a 16-pin, 3mm × 3mm plastic QFN package with exposed thermal pad (GND). The package enables high-power density and low θ_JA = 68°C/W for industrial ambient operation.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LT3689IUD#TRPBF, the LT3689IUD-5#TRPBF saves two resistors and simplifies layout for 5V-only designs, while MAX5033BASA+T trades away integrated supervision to achieve higher input voltage range and lower unit cost - making it suitable only when external supervision is acceptable.

Availability

LT3689IUD-5#TRPBF is available at Aetrix Electronics and suitable for automotive electronic control units, industrial PLC I/O modules, and medical infusion pump controllers requiring stable component supply with guaranteed long-term availability and full traceability.

Supply support for LT3689IUD-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, datasheets, and application engineering for the LT3689 family.

The LT3689 product line was designed for automotive and industrial power systems requiring integrated power conversion and microprocessor supervision in a single IC - eliminating discrete supervisors and reducing design risk in safety-critical applications.

FAQ

What is the guaranteed operating temperature range for LT3689IUD-5#TRPBF?

The LT3689IUD-5#TRPBF is specified and guaranteed over the industrial temperature range of –40°C to +125°C junction temperature. This rating is validated across electrical parameters including output voltage accuracy (±1%), reset threshold (90% of 5V), and watchdog timing (t_WDU, t_WDL) per the official datasheet Rev. D. Derating applies above 125°C per Note 3.

Does LT3689IUD-5#TRPBF require external components for 5V regulation?

No. The LT3689IUD-5#TRPBF integrates the feedback resistor divider for fixed 5V output; the FB pin is internally connected and must remain unconnected in this variant. External components required are: input capacitor (≥10µF), output capacitor (≥22µF), boost capacitor (2.2µF), inductor (e.g., 12µH), catch diode, and timing capacitors CPOR and CWDT - no resistors are needed for regulation.

How does the DA pin protect the LT3689IUD-5#TRPBF during output short-circuit?

The DA pin senses current through the external catch diode. If DA current exceeds 1.2A (typical), the LT3689IUD-5#TRPBF disables switching until current falls below threshold. During sustained short, this limits inductor valley current to ~1.2A, preventing thermal runaway and enabling safe auto-recovery once fault clears - a feature confirmed in the Electrical Characteristics table (DA Current Limit = 0.85/1.2/1.5A min/typ/max).

Can LT3689IUD-5#TRPBF synchronize to an external clock?

Yes. The SYNC pin accepts logic-level input with ≥80ns positive and negative pulse widths. To ensure reliable synchronization, the LT3689IUD-5#TRPBF's RT-set switching frequency must be at least 20% lower than the lowest expected sync frequency, as stated in the Applications Information section. This prevents pulse-skipping and maintains constant-frequency operation.

What is the minimum recommended CPOR capacitor value for LT3689IUD-5#TRPBF?

The minimum recommended CPOR capacitor is 1nF, yielding a reset timeout of 2.3ms. However, the datasheet specifies guaranteed t_RST performance (17–21ms) only for CPOR ≥ 8.2nF (e.g., 8.2nF Murata GRM2195C1H822FA01). Using smaller values may result in reduced timing accuracy and increased temperature drift, as shown in Figure G35.