Texas Instruments LM2655MTCX-3.3/NOPB

Overview

LM2655MTCX-3.3/NOPB from Texas Instruments (formerly National Semiconductor) is a 2.5A synchronous step-down DC-DC 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 4V–14V input for portable and space-constrained power rails.

For engineers reviewing the LM2655MTCX-3.3/NOPB datasheet, LM2655MTCX-3.3/NOPB pinout, LM2655MTCX-3.3/NOPB application, or LM2655MTCX-3.3/NOPB equivalent, key selection considerations include its synchronous/asynchronous 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/NOPB implements constant-frequency current-mode PWM control with patented internal current sensing-no external sense resistor required. Its 300kHz oscillator sets switching timing, while dual-mode operation allows either synchronous drive via LDR pin or asynchronous diode-based operation by floating LDR.

Protection logic includes 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 capacitor), and thermal shutdown at 165°C with 25°C hysteresis. The device integrates all control, drive, and power functions except the low-side FET in synchronous mode.

Key Specifications

Pinout & Package

LM2655MTCX-3.3/NOPB is housed in a 16-pin TSSOP (Thin Shrink Small Outline Package) with 0.65mm pitch and exposed thermal pad (not electrically connected). Package dimensions: 5.0mm × 4.4mm × 1.2mm (max height).

Key Features

Applications

Equivalent & Alternatives

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

Compared with TPS54260DGQR and LM2678SD-3.3/NOPB, the LM2655MTCX-3.3/NOPB uniquely combines fixed 3.3V output, integrated high-side FET, synchronous drive capability, and patented current sensing in a compact TSSOP-16-making it optimal for space-constrained, efficiency-critical 4–14V input systems requiring ≤2.5A.

Availability

LM2655MTCX-3.3/NOPB is available at Aetrix Electronics and suitable for hard disk drives, TFT monitors, battery-powered devices, computer peripherals, and internet appliances requiring stable component supply, long-term lifecycle support, and RoHS-compliant packaging.

Supply support for LM2655MTCX-3.3/NOPB 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 its legacy power management portfolio with full technical documentation, simulation models, and application support.

The LM2655MTCX-3.3/NOPB belongs to TI's high-efficiency synchronous buck regulator family, designed specifically for portable and space-constrained applications demanding low quiescent current, robust protection, and flexible synchronous/asynchronous operation.

FAQ

What is the output voltage tolerance of the LM2655MTCX-3.3/NOPB over temperature and load?

The LM2655MTCX-3.3/NOPB delivers a nominal 3.3V output with guaranteed tolerance of ±1.7% over full operating temperature (−40°C to +125°C) and load range (100mA to 2.5A). This specification is confirmed in the "LM2655-3.3 Electrical Characteristics" table under Load Regulation, where worst-case deviation is bounded at 1.7% maximum. The fixed 3.3V version uses an internal feedback divider, eliminating external resistor errors.

Can the LM2655MTCX-3.3/NOPB operate in synchronous mode without external components beyond the low-side MOSFET?

Yes-the LM2655MTCX-3.3/NOPB supports synchronous operation using only an external N-channel MOSFET driven by the LDR pin. No additional gate drivers or level shifters are required. The IC provides 500mA sink and 180mA source capability on LDR, and its internal 30ns dead-time control prevents shoot-through. A Schottky diode in parallel with the low-side MOSFET is recommended to improve efficiency during dead-time conduction.

How does the LDELAY pin function in the LM2655MTCX-3.3/NOPB, and what capacitor value yields a 10ms undervoltage delay?

The LDELAY pin implements a programmable undervoltage latch delay: a 5µA current source charges an external capacitor when output voltage falls below 81% of 3.3V (2.673V); latch triggers at 2V across the capacitor. For a 10ms delay, use C_DELAY = (10ms × 5µA) / 2V = 25nF. A standard 22nF or 27nF capacitor meets this requirement. Tying LDELAY to GND disables the latch entirely.

What is the minimum input voltage required for the LM2655MTCX-3.3/NOPB to regulate 3.3V output?

The LM2655MTCX-3.3/NOPB requires a minimum input voltage of 3.8V on PVIN due to its input undervoltage lockout (UVLO) threshold. However, the separate AVIN pin allows operation with PVIN as low as ~3.8V + V_OUT ≈ 7.1V if AVIN is supplied independently from a stable 4–14V source. In standard configuration with shared PVIN/AVIN, 3.8V is the absolute minimum for startup and regulation.

Does the LM2655MTCX-3.3/NOPB require an external compensation network, and what are typical values?

Yes-the LM2655MTCX-3.3/NOPB requires external compensation on the COMP pin to ensure loop stability. For typical 3.3V/2.5A designs with ≥68µF output capacitance, TI recommends C_c1 = 2.2nF and R_c = 15kΩ. These values establish a lag compensator that rolls off gain near crossover. If output capacitor ESR zero cannot be canceled by the inherent pole, a second capacitor C_c2 may be added per the compensation guidelines in the datasheet.