Analog Devices Inc. LT1241IN8#PBF

Overview

LT1241IN8#PBF from Analog Devices is an 8-pin PDIP-packaged, fixed-frequency current-mode PWM controller optimized for off-line and DC/DC converters. It delivers 1A totem-pole output drive, operates up to 500kHz switching frequency, features 50ns current sense delay and <250µA start-up current, and is used in isolated AC/DC power supplies with MOSFET gate driving.

For engineers reviewing the LT1241IN8#PBF datasheet, LT1241IN8#PBF pinout, LT1241IN8#PBF application, or LT1241IN8#PBF equivalent, key selection criteria include undervoltage lockout thresholds (9.6V start-up), 5V reference accuracy (±1%), oscillator trim tolerance (±5% at 50kHz), and active pull-down during UVLO on both OUTPUT and VREF pins.

Technical Context

The LT1241IN8#PBF implements a fixed-frequency current-mode control architecture with leading-edge blanking on the ISENSE comparator and a trimmed 8.2mA oscillator sink current. Its error amplifier provides 90dB open-loop gain and 1MHz unity-gain bandwidth, with internal 2.5V feedback reference derived from the 5V bandgap.

Oscillator timing is set by external RT/CT network, where CT discharge time defines deadtime and maximum duty cycle (≤48% for LT1241). Output switching frequency equals half the oscillator frequency (e.g., 100kHz oscillator → 50kHz output), enabling stable operation up to 500kHz output switching.

Key Specifications

Pinout & Package

N8 package: 8-lead plastic DIP, –40°C to 125°C operating range, 130°C/W thermal resistance.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar current-mode PWM controller applications.

Compared with UC1842N and TL3842N, the LT1241IN8#PBF delivers superior thermal margin via lower quiescent current, faster fault response through 50ns current sense path, and enhanced system reliability via active UVLO pull-down-making it preferred for industrial-grade 50–200W power supplies.

Availability

LT1241IN8#PBF is available at Aetrix Electronics and suitable for industrial AC/DC power supplies, isolated DC/DC converters, and off-line LED drivers requiring stable component supply across extended temperature ranges.

Supply support for LT1241IN8#PBF 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 (now part of Analog Devices, Inc. following merger with Linear Technology) is a global leader in high-performance analog, mixed-signal, and power management ICs.

The LT1241 series belongs to Linear Technology's legacy PWM controller product line, designed specifically for high-reliability, high-speed current-mode switching power supplies in industrial and telecom infrastructure.

FAQ

What is the maximum switching frequency supported by the LT1241IN8#PBF?

The LT1241IN8#PBF supports output switching frequencies up to 500kHz. This is achieved because its internal oscillator runs at up to 1MHz, and the LT1241 variant divides that clock by two to generate the final output waveform. The actual frequency is set by the RT/CT network, with typical configurations ranging from 50kHz to 100kHz oscillator frequency (25–50kHz output).

Does the LT1241IN8#PBF require external components for current sense filtering?

No, the LT1241IN8#PBF incorporates built-in leading-edge blanking with a 100ns window synchronized to switch turn-on, eliminating the need for external RC filters at the ISENSE pin in most applications. This preserves current loop speed while rejecting transformer leakage spikes-only extreme EMI environments may require supplemental filtering.

How does the LT1241IN8#PBF handle undervoltage lockout conditions?

During undervoltage lockout, the LT1241IN8#PBF actively pulls both the OUTPUT (Pin 6) and VREF (Pin 8) pins low using integrated Darlington PNP transistors. This ensures the external MOSFET gate remains off and allows the VREF pull-down to reset soft-start capacitors-removing the need for external pull-down resistors used in older controllers like UC1842.

Can the LT1241IN8#PBF drive logic-level MOSFETs directly?

Yes, the LT1241IN8#PBF can directly drive logic-level MOSFETs thanks to its ±1A totem-pole output stage and 18V output clamp. Its 40ns rise and 30ns fall times into 1nF loads ensure fast switching transitions, and the active low-state pull-down during UVLO guarantees safe gate discharge even before VCC reaches regulation.

What is the purpose of the COMP pin on the LT1241IN8#PBF?

On the LT1241IN8#PBF, the COMP pin (Pin 1) serves as the error amplifier output and provides access to the internal compensation node. It allows external type-II or type-III compensation networks to be added, enables clamping of the current sense threshold voltage below 1V, and supports soft-start functionality via external capacitor charging.