Texas Instruments LM2655MTCX-3.3

Overview

LM2655MTCX-3.3 from Texas Instruments (formerly National Semiconductor) is a 2.5A synchronous step-down DC-DC switching regulator in TSSOP-16 package, featuring internal 33mΩ high-side MOSFET, 300kHz fixed-frequency PWM control, and programmable soft-start. It delivers regulated 3.3V output with ±1.7% load regulation and supports input voltages from 4V to 14V - ideal for powering logic rails in TFT monitors and hard disk drive controllers.

For engineers reviewing the LM2655MTCX-3.3 datasheet, LM2655MTCX-3.3 pinout, LM2655MTCX-3.3 application, or LM2655MTCX-3.3 equivalent, key selection considerations include its synchronous/async mode flexibility, integrated current-sense architecture eliminating external sense resistors, shutdown current <12µA, and thermal/overvoltage/undervoltage protection with latch behavior.

Technical Context

The LM2655MTCX-3.3 implements constant-frequency current-mode PWM control with a 300kHz oscillator and patented zero-resistor current sensing. Its dual-mode operation allows designers to select asynchronous mode (external Schottky diode) for cost-sensitive designs or synchronous mode (external low-side N-MOSFET driven by LDR pin) for >90% efficiency at full load.

Protection features include input undervoltage lockout (3.8V rising threshold), output overvoltage shutdown (108% of 3.3V), output undervoltage latch (81% of 3.3V with user-programmable delay via LDELAY pin), and thermal shutdown at 165°C with 25°C hysteresis. The IC integrates all power, control, and gate-drive functions except the low-side switch in synchronous mode.

Key Specifications

Pinout & Package

LM2655MTCX-3.3 is housed in a 16-pin Thin Shrink Small Outline Package (TSSOP-16), 5mm × 4.4mm footprint, 0.65mm pitch, thermally enhanced with exposed pad (not electrically connected). Pin mapping is validated per National Semiconductor DS101284 Rev. April 2005.

Key Features

Applications

Equivalent & Alternatives

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

Compared with TPS54231DR and LM2678-3.3, LM2655MTCX-3.3 uniquely provides synchronous/async mode selection, sub-12µA shutdown, and user-configurable undervoltage latch timing - making it optimal for space-constrained, efficiency-critical, and battery-sensitive applications where design flexibility matters.

Availability

LM2655MTCX-3.3 is available at Aetrix Electronics and suitable for TFT monitors, hard disk drive controllers, and internet appliances requiring stable component supply, long-term lifecycle support, and traceable sourcing.

Supply support for LM2655MTCX-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

Texas Instruments acquired National Semiconductor in 2011 and maintains full technical support, datasheets, and simulation models for legacy power management ICs including the LM2655 family.

The LM2655 product line was designed for high-density, high-efficiency point-of-load conversion in computing and storage systems - emphasizing integration, protection, and design flexibility over raw current rating.

FAQ

What is the maximum output current capability of the LM2655MTCX-3.3?

The LM2655MTCX-3.3 is rated for continuous 2.5A output current under typical thermal conditions (T_A = 25°C, 2-layer PCB, no heatsink). Peak current limit is 3.3A (typical) at V_IN = 5V, but sustained operation above 2.5A requires careful thermal management due to 893mW max power dissipation in the TSSOP-16 package. Derating is required above 25°C ambient.

Does the LM2655MTCX-3.3 require an external feedback resistor divider?

No. The LM2655MTCX-3.3 is the fixed 3.3V output variant - its internal feedback network is trimmed to 1.238V reference and configured for 3.3V output. Pin 9 (FB) connects directly to the output; no external resistors are needed. Only the adjustable version (LM2655MTCX-ADJ) requires an external divider.

How does synchronous versus asynchronous operation affect efficiency in the LM2655MTCX-3.3?

In synchronous mode (with external low-side N-MOSFET driven by LDR pin), LM2655MTCX-3.3 achieves >90% efficiency at full 2.5A load due to reduced conduction loss. In asynchronous mode (Schottky diode only), efficiency drops ~3–5% across mid-to-high load range because of diode forward voltage drop - making synchronous mode preferred for battery life or thermal constraints.

What is the purpose of the LDELAY pin on the LM2655MTCX-3.3?

The LDELAY pin implements a user-programmable delay before undervoltage latch activation. A capacitor from LDELAY to GND sets the timeout: T_DELAY(ms) = C_DELAY(nF) × 2V ÷ 5µA. If output voltage falls below 81% of 3.3V, this current source charges the capacitor; reaching 2V triggers latch shutdown. Tying LDELAY to GND disables the latch function entirely.

Can the LM2655MTCX-3.3 operate with input voltage below 4V?

Yes - by separating power and analog supplies. Connect a stable 4–14V source to AVIN (Pin 7) to power control circuitry, while applying the lower input (e.g., 3.8V) to PVIN (Pins 3–5, 14–16). This exploits the independent AVIN/PVIN architecture, allowing functional operation down to ~3.8V on PVIN as long as AVIN remains within spec - verified in TI's application notes for extended VIN range.