Analog Devices Inc. LT1247CS8#TRPBF

Overview

LT1247CS8#TRPBF from Analog Devices (formerly Linear Technology) is an 8-pin SOIC current-mode PWM controller IC designed for off-line and DC/DC converter applications. It delivers 1 MHz fixed-frequency operation, 1 A totem-pole output drive, <250 µA start-up current, and integrated leading-edge blanking - enabling stable high-speed switching in flyback, forward, and boost topologies.

For engineers reviewing the LT1247CS8#TRPBF datasheet, LT1247CS8#TRPBF pinout, LT1247CS8#TRPBF application, or LT1247CS8#TRPBF equivalent, key selection criteria include undervoltage lockout threshold (8.4 V), current sense delay (30 ns), oscillator sink current (8.2 mA), reference voltage accuracy (±1.5% over temp), and compatibility with UC1843-based designs.

Technical Context

The LT1247CS8#TRPBF implements a fixed-frequency current-mode control architecture with a trimmed oscillator (500 kHz typical with RT=6.2 kΩ, CT=500 pF), internal 2.5 V error amplifier reference, and 1 V current sense clamp. Its error amplifier features 90 dB open-loop gain and 2 MHz unity-gain bandwidth, supporting tight regulation in voltage- or current-controlled loops.

It integrates active pull-down on both OUTPUT (Pin 6) and VREF (Pin 8) during undervoltage lockout, eliminating external pull-down resistors. The 30 ns current sense comparator delay and 60 ns blanking time - dynamically adjusted by FB pin voltage - suppress noise-induced false triggering without external filtering.

Key Specifications

Pinout & Package

LT1247CS8#TRPBF is housed in an 8-lead plastic SOIC (S8) package with standard JEDEC MS-012AC dimensions (3.9 mm × 4.9 mm × 1.5 mm), rated for 0°C to 100°C junction temperature and θ_JA = 150°C/W.

Key Features

Applications

Equivalent & Alternatives

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

Compared with UC1843N8 and TL3843BDR, the LT1247CS8#TRPBF provides tighter oscillator accuracy, integrated blanking, and active UVLO management - reducing component count and improving reliability in high-noise, high-frequency converter designs.

Availability

LT1247CS8#TRPBF is available at Aetrix Electronics and suitable for AC-DC adapters, industrial DC/DC converters, LED drivers, and telecom power supplies requiring stable component supply, long-term lifecycle support, and guaranteed traceable sourcing.

Supply support for LT1247CS8#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 its legacy analog power IC portfolio with full datasheet, SPICE model, and application note support.

The LT1247CS8#TRPBF belongs to the LT124x family of high-speed current-mode PWM controllers, engineered specifically for rugged, high-efficiency off-line and isolated DC/DC power conversion in industrial and telecom environments.

FAQ

What is the UVLO behavior of the LT1247CS8#TRPBF?

The LT1247CS8#TRPBF features undervoltage lockout with a typical start-up threshold of 8.4 V and minimum operating voltage of 7.6 V, plus 0.8 V hysteresis. During UVLO, both the OUTPUT (Pin 6) and VREF (Pin 8) pins are actively pulled low to ~1 V by internal Darlington PNP transistors - eliminating the need for external pull-down resistors and ensuring clean, glitch-free startup in LT1247CS8#TRPBF-based converters.

Can the LT1247CS8#TRPBF drive a 10 nF MOSFET gate directly?

Yes, the LT1247CS8#TRPBF's ±1 A totem-pole output can drive capacitive loads up to 10 nF with sub-70 ns rise/fall times (measured at 1 nF). For 10 nF, gate charge delivery remains robust, though layout must minimize inductance - use short, wide traces and local 0.1 µF ceramic bypassing at VCC. The 18 V output clamp protects the MOSFET gate, making LT1247CS8#TRPBF suitable for direct drive in medium-power applications.

How does the current sense blanking work on the LT1247CS8#TRPBF?

The LT1247CS8#TRPBF implements fixed-duration leading-edge blanking at the ISENSE (Pin 3) comparator output: 60 ns at nominal FB = 2.5 V, scaling linearly to zero as FB approaches 0 V. This blanking window prevents false triggering from transformer leakage spikes or diode reverse-recovery noise - allowing elimination of external RC filters and preserving <30 ns current sense delay. The feature is intrinsic to LT1247CS8#TRPBF and requires no external components.

What is the maximum achievable switching frequency using the LT1247CS8#TRPBF?

The LT1247CS8#TRPBF is characterized for operation up to 1 MHz, with typical oscillator frequencies of 465–535 kHz (RT = 6.2 kΩ, CT = 500 pF) and 47.5–52.5 kHz (RT = 10 kΩ, CT = 3.3 nF). At 1 MHz, design validation is required for deadtime margin and output stage thermal performance. The 30 ns current sense delay and 20 ns fall time make LT1247CS8#TRPBF viable for 1 MHz designs when paired with fast gate drivers and optimized PCB layout.

Does the LT1247CS8#TRPBF support external synchronization?

No, the LT1247CS8#TRPBF does not support external clock synchronization. Its oscillator is self-contained and trimmed - RT/CT sets frequency and deadtime exclusively. Unlike some later-generation controllers, LT1247CS8#TRPBF lacks a SYNC pin or internal circuitry for master-slave timing alignment. Synchronization must be implemented externally via modulation of the COMP or FB node, but this compromises regulation integrity and is not recommended for production use with LT1247CS8#TRPBF.