Analog Devices Inc. LT1245CS8#TRPBF

Overview

LT1245CS8#TRPBF from Analog Devices is an 8-pin, fixed-frequency, current-mode PWM controller IC optimized for off-line and DC/DC converters. It delivers 500 kHz switching capability, features a 1 A totem-pole output stage, 50 ns current sense delay, and active undervoltage lockout with 8.4 V start-up threshold - enabling reliable gate drive for power MOSFETs in AC-DC adapters and industrial SMPS.

For engineers reviewing the LT1245CS8#TRPBF datasheet, LT1245CS8#TRPBF pinout, LT1245CS8#TRPBF application, or LT1245CS8#TRPBF equivalent, key selection criteria include its 500 kHz max switching frequency, 1 A peak output drive, 8.4 V UVLO start-up threshold, trimmed oscillator sink current (8.2 mA), and compatibility with UC1845-based designs requiring improved speed and lower quiescent current.

Technical Context

The LT1245CS8#TRPBF implements fixed-frequency current-mode control with leading-edge blanking on the ISENSE comparator input to suppress noise-induced false triggering during MOSFET turn-on. Its oscillator uses a trimmed 8.2 mA sink current and external RT/CT network to set both frequency and deadtime, supporting up to 1 MHz oscillator operation for 500 kHz output switching.

It integrates a 5 V ±1% bandgap reference (pin 8), a high-gain error amplifier (90 dB open-loop gain, 1 MHz unity-gain bandwidth), and a clamped 18 V high-side output stage. During undervoltage lockout, both VREF and OUTPUT are actively pulled low via Darlington PNP transistors - eliminating need for external pull-down resistors in gate-drive circuits.

Key Specifications

Pinout & Package

LT1245CS8#TRPBF is housed in an 8-lead plastic SO (S8) package, RoHS-compliant, with 1.27 mm lead pitch and JEDEC MS-012AC outline. Thermal resistance 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 UC1845N and UCC2802DR, LT1245CS8#TRPBF offers superior high-frequency operation (500 kHz), built-in noise immunity (100 ns blanking), and active safety features (dual pull-down during UVLO), making it optimal for space-constrained, high-reliability off-line converters demanding tight regulation and fast fault response.

Availability

LT1245CS8#TRPBF is available at Aetrix Electronics and suitable for AC-DC adapters, industrial DC-DC converters, and LED drivers requiring stable component supply, long-term lifecycle support, and RoHS-compliant packaging.

Supply support for LT1245CS8#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 (now part of Analog Devices, Inc., following merger with Linear Technology) is a global leader in high-performance analog, mixed-signal, and power management semiconductors.

The LT1241 series - including LT1245CS8#TRPBF - was designed specifically for high-efficiency, high-frequency current-mode switching power supplies targeting off-line and isolated DC-DC applications with stringent reliability and noise immunity requirements.

FAQ

What is the maximum switching frequency supported by the LT1245CS8#TRPBF?

The LT1245CS8#TRPBF supports up to 500 kHz output switching frequency, achieved by running its internal oscillator at 1 MHz. This is confirmed in the Applications Information section (Rev B, p.9), which states "the output switching frequency will be equal to one-half the oscillator frequency for LT1241, LT1244 and LT1245" and that "the oscillator will run at frequencies up to 1MHz." The 500 kHz limit is a functional specification tied to the device's current-mode architecture and propagation delays.

Does the LT1245CS8#TRPBF require an external current sense filter?

No, the LT1245CS8#TRPBF does not require an external current sense filter due to its integrated leading-edge blanking circuit. As documented on page 11, the blanking time is fixed at 100 ns under normal conditions (VFB = 2.5 V) and automatically reduces during startup or short-circuit faults. This feature eliminates the need for RC filtering at the ISENSE pin in most applications, preserving fast current-loop response while suppressing transformer leakage spikes.

What is the UVLO hysteresis value for the LT1245CS8#TRPBF?

The LT1245CS8#TRPBF has a UVLO hysteresis of 0.4 V, as specified in the Electrical Characteristics table (page 4). The start-up threshold is 8.4 V (min), and the minimum operating voltage is 7.6 V (min), yielding a 0.8 V total window; however, hysteresis is explicitly listed as 0.4 V for LT1243/LT1245 variants. This narrow hysteresis prevents oscillatory startup near the threshold and ensures clean entry/exit from lockout mode.

Can the LT1245CS8#TRPBF drive a high-side N-channel MOSFET directly?

No, the LT1245CS8#TRPBF cannot directly drive a high-side N-channel MOSFET because its OUTPUT pin is a single-ended totem-pole stage referenced to GND, not a floating high-side driver. It is designed for low-side or grounded-source configurations (e.g., flyback primary switch, buck low-side switch). For high-side N-MOSFET drive, a dedicated high-side gate driver or bootstrap circuit is required - the LT1245CS8#TRPBF itself provides no level-shifting or floating supply capability.

Is the 5 V reference output (VREF) of the LT1245CS8#TRPBF internally trimmed?

Yes, the 5 V reference output (Pin 8) of the LT1245CS8#TRPBF is trimmed to ±1% initial tolerance (4.925 V to 5.075 V at 25°C), as stated in the Electrical Characteristics table (page 3). This trimming applies across the full LT1241 series, including LT1245, and ensures stable timing current for the RT/CT network and accurate biasing for internal circuitry without external calibration.