Analog Devices Inc. LTC1147CN8-3.3#PBF

Overview

LTC1147CN8-3.3 from Analog Devices (formerly Linear Technology) is a high-efficiency, constant off-time current-mode step-down switching regulator controller driving an external P-channel MOSFET to deliver a fixed 3.3V output. It operates from 3.5V to 16V input, achieves >95% efficiency at full load, maintains regulation down to 160µA quiescent current in Burst Mode, and supports 100% duty cycle for ultra-low dropout operation - ideal for battery-powered portable instrumentation and GPS systems.

For engineers reviewing the LTC1147CN8-3.3 datasheet, LTC1147CN8-3.3 pinout, LTC1147CN8-3.3 application, or LTC1147CN8-3.3 equivalent, key selection criteria include its fixed 3.3V output voltage (±3.3% over load/temperature), 160µA sleep-mode supply current, 5µs typical off-time, 8-pin PDIP package with ground-isolated layout requirements, and compatibility with standard-threshold P-MOSFETs in 5.2–14V input rails.

Technical Context

The LTC1147CN8-3.3 implements a constant off-time current-mode architecture where the timing capacitor (CT) at Pin 2 sets switching frequency, and the SENSE+ (Pin 5)/SENSE– (Pin 4) differential pair monitors inductor current via an external sense resistor. Its internal 1.25V reference and fixed resistor divider establish the 3.3V output without external feedback components.

Burst Mode™ operation activates below ~15mA load to reduce switching losses, dropping IQ to 160µA while maintaining regulation via output capacitor discharge; shutdown is logic-controlled via SHDN (Pin 6), drawing <20µA when pulled above 0.8V. The PDRIVE (Pin 8) output swings rail-to-rail (VIN to GND) to drive P-MOSFET gates with 100–200ns transition times.

Key Specifications

Pinout & Package

Package: 8-lead plastic DIP (N8), 0.3-inch width, θ_JA = 110°C/W, lead temperature rated to 300°C for 10 sec.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar step-down controller applications.

Compared with LTC1147CS8-3.3, the LTC1147CN8-3.3 offers lower thermal resistance in through-hole designs and simpler heatsinking; versus LTC1148CN8-3.3, it trades slightly higher gate drive capability for 90µA lower sleep current - critical for multi-year battery operation.

Availability

LTC1147CN8-3.3 is available at Aetrix Electronics and suitable for portable instrumentation, GPS navigation modules, and industrial handheld scanners requiring stable component supply with long-term manufacturability and consistent parametric performance.

Supply support for LTC1147CN8-3.3 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 legacy Linear parts including the LTC series.

The LTC1147 family was designed specifically for high-efficiency, low-quiescent-current step-down regulation in space-constrained portable electronics - emphasizing Burst Mode™ operation, P-MOSFET compatibility, and wide-input flexibility.

FAQ

What is the maximum input voltage rating for the LTC1147CN8-3.3?

The LTC1147CN8-3.3 has an absolute maximum input voltage of 16V on Pin 1 (VIN). Continuous operation is specified from 3.5V to 14V, with 16V representing the absolute limit before potential damage. Exceeding 16V violates the Absolute Maximum Ratings and may cause permanent failure. For applications requiring >14V input, consider the LTC1149 synchronous controller.

Does the LTC1147CN8-3.3 require external feedback resistors to set the 3.3V output?

No, the LTC1147CN8-3.3 does not require external feedback resistors. It integrates a precision internal resistor divider that fixes the regulated output at 3.33V (±3.3%) - confirmed by datasheet Electrical Characteristics tables showing VOUT = 3.23–3.43V at 700mA load. Pin 6 (SHDN/VFB) functions solely as a shutdown control input in this fixed-output variant.

How does Burst Mode™ operation affect output voltage ripple on the LTC1147CN8-3.3?

In Burst Mode™, the LTC1147CN8-3.3 disables switching cycles to reduce IQ to 160µA, causing output voltage to decay gradually between bursts. This results in controlled low-frequency ripple (typically <50mV_P-P at I_LOAD = 0A), distinct from high-frequency switching ripple. The device's hysteresis-based wake-up ensures regulation is maintained without oscillation, and ripple remains within spec for most microcontroller and sensor applications.

Can the LTC1147CN8-3.3 drive a logic-level P-channel MOSFET?

Yes, the LTC1147CN8-3.3 can drive logic-level P-channel MOSFETs, but caution is required: its PDRIVE (Pin 8) swings from VIN to GND, so gate-source voltage (V_GS) equals –VIN. For VIN ≥ 5V, standard-threshold P-MOSFETs (|V_GS(th)| < 4V) are preferred. If VIN drops below 5V, a logic-level device (|V_GS(th)| < 2.5V) may be necessary - verify that |V_GS| never exceeds the MOSFET's absolute maximum rating.

What is the recommended value for the timing capacitor (CT) to achieve ~500kHz operation with the LTC1147CN8-3.3?

For ~500kHz continuous-mode operation with VIN = 10V and VOUT = 3.3V, the datasheet formula CT = 1 / [(1.3)(10⁴)(f)] × (VIN – VOUT)/(VIN + V_D) yields ~470pF (using V_D ≈ 0.4V for Schottky diode). Figure 3 confirms 470pF delivers 450–520kHz across 7–12V input, matching typical design targets. Use NPO/C0G ceramic for stability.