Analog Devices Inc. LT1737IS#TRPBF

Overview

LT1737IS#TRPBF from Analog Devices (formerly Linear Technology) is a current-mode isolated flyback controller IC designed to drive external N-channel MOSFETs in high-efficiency, galvanically isolated DC-DC converters. It operates from 4.5V to 20V supply, delivers up to tens of watts output power, and supports switching frequencies from 50kHz to 250kHz via external OSCAP capacitor. Its primary-side sensing eliminates optoisolators in medical instrument and instrumentation power supplies.

For engineers reviewing the LT1737IS#TRPBF datasheet, LT1737IS#TRPBF pinout, LT1737IS#TRPBF application, or LT1737IS#TRPBF equivalent, key selection criteria include primary-side feedback accuracy (±1.2% V_FB), discontinuous-mode regulation stability, optional load compensation, UVLO threshold (1.25V typ), and SO-16 package compatibility with industrial temperature range (–40°C to 125°C).

Technical Context

The LT1737IS#TRPBF implements a proprietary flyback error amplifier that samples the reflected flyback pulse from a third transformer winding-enabling precise primary-side regulation without optocouplers. Its control loop integrates VC pin current from a transconductance amplifier (400–1800 µmho) and uses collapse-detect timing to distinguish true flyback voltage from leakage spikes.

It features three programmable timing functions: minimum on-time (200 ns typ), enable delay (200 ns typ), and minimum enable time (200 ns typ), all set via external resistors (tON, ENDLY, MINENAB). Load compensation is implemented via ROCMP/RCMPC pins to correct for secondary impedance effects across load variations.

Key Specifications

Pinout & Package

LT1737IS#TRPBF is housed in a 16-lead plastic SO (Small Outline) package with exposed pad thermal enhancement. Pin layout follows standard SO-16 footprint with 1.27mm pitch; PGND and SGND are separate for noise isolation between power and signal grounds.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar isolated flyback controller applications.

Compared with UCC28740DR and MAX17690ATP+T, the LT1737IS#TRPBF uniquely supports primary-side load compensation and programmable timing for leakage-tolerant operation-making it the preferred choice for medical and instrumentation designs demanding <±2% regulation across full load and temperature range.

Availability

LT1737IS#TRPBF is available at Aetrix Electronics and suitable for medical instrumentation power supplies, industrial sensor interfaces, isolated data acquisition systems, and other applications requiring stable component supply with long-term lifecycle assurance.

Supply support for LT1737IS#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 leader in high-performance analog, mixed-signal, and digital signal processing semiconductors, formed through the acquisition of Linear Technology in 2017.

The LT1737IS#TRPBF belongs to ADI's legacy Linear Technology isolated power controller product line, engineered specifically for high-accuracy, optocoupler-free flyback converters in safety-critical and precision instrumentation applications.

FAQ

What is the maximum output power achievable with the LT1737IS#TRPBF?

The LT1737IS#TRPBF is rated to support "load power up to tens of Watts" when paired with a suitably rated external MOSFET, transformer, and passive components. In published reference designs (e.g., 15V/300mA), it delivers 4.5W reliably; with optimized layout, thermal management, and high-efficiency magnetics, designs exceeding 25W have been validated. Actual limit depends on MOSFET R_DS(on), transformer coupling, and PCB copper area.

Does the LT1737IS#TRPBF require an optocoupler for feedback?

No, the LT1737IS#TRPBF does not require an optocoupler. It uses primary-side sensing by monitoring the reflected flyback pulse from a third transformer winding (or primary winding), comparing it to its internal 1.245V reference at the FB pin. This architecture eliminates optocouplers, reducing cost, size, and long-term reliability risks in medical and industrial isolation applications.

How is load regulation improved using the ROCMP and RCMPC pins on the LT1737IS#TRPBF?

The ROCMP and RCMPC pins implement active load compensation on the LT1737IS#TRPBF. A voltage proportional to average switch current is developed across RCMPC and applied to ROCMP, generating a correction current injected into the FB node. This counteracts voltage droop caused by secondary impedance (diode VF, winding resistance, capacitor ESR), enabling <1% load regulation from 10mA to full rated output-without trimming or secondary-side circuitry.

What is the purpose of the ENDLY, MINENAB, and tON pins on the LT1737IS#TRPBF?

These three pins on the LT1737IS#TRPBF program critical timing windows for flyback pulse sampling: ENDLY sets delay before enabling the feedback amplifier (to avoid leakage spikes), MINENAB defines minimum duration the amplifier stays active, and tON enforces shortest MOSFET on-time per cycle. Together, they ensure reliable regulation across continuous/discontinuous modes and varying transformer leakage-key for medical-grade stability.

Can the LT1737IS#TRPBF operate with input voltages below 4.5V?

No-the absolute minimum V_CC for functional operation of the LT1737IS#TRPBF is 4.1V (min), with typical operation specified from 4.5V to 20V. Below 4.1V, internal bias circuitry fails to activate; the UVLO function (threshold 1.25V on UVLO pin) may shut down the part earlier depending on external divider configuration. For sub-4.5V inputs, a pre-regulator or alternative controller is required.