Texas Instruments LM2651MTCX-ADJ

Overview

LM2651MTCX-ADJ from Texas Instruments is a 1.5-A synchronous step-down DC-DC switching regulator in a 16-pin TSSOP package, featuring adjustable output voltage (via external resistor divider), 300-kHz fixed-frequency current-mode PWM operation, and automatic hysteretic mode transition at light loads to sustain >80% efficiency down to 15 mA. It integrates high- and low-side MOSFETs with 75-mΩ typical R_DS(on), patented internal current sensing, and programmable soft-start - deployed in battery-powered PDAs and handheld scanners requiring long standby life.

For engineers reviewing the LM2651MTCX-ADJ datasheet, LM2651MTCX-ADJ pinout, LM2651MTCX-ADJ application, or LM2651MTCX-ADJ equivalent, key selection criteria include its 4–14-V input range, 1.2-V feedback reference, 7-µA shutdown current, thermal shutdown at 165°C, and compatibility with Schottky diode-assisted layouts for improved noise immunity and efficiency above 95% at full load.

Technical Context

The LM2651MTCX-ADJ operates in constant-frequency (300 kHz) current-mode PWM under moderate-to-heavy loads and switches autonomously to low-frequency hysteretic mode below 100 mA to maintain high light-load efficiency. Its patented current-sensing architecture eliminates the need for an external sense resistor by measuring MOSFET conduction voltage drop directly.

Control relies on a transconductance error amplifier (G_m = 1250 µmho) with COMP pin interfacing to an RC compensation network, while the FB pin monitors a 1.238-V reference to regulate output via external R1/R2. The device incorporates undervoltage lockout (3.8 V rising threshold), cycle-by-cycle current limiting (2 A typical), and thermal shutdown with 25°C hysteresis.

Key Specifications

Pinout & Package

LM2651MTCX-ADJ is housed in a 16-pin TSSOP package (5.00 mm × 4.40 mm body size) with exposed thermal pad (not electrically connected). Pin functions are validated per TI SNVS032E Rev E datasheet.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar synchronous buck regulator applications.

Compared with TPS5430DR and LM2678SD-ADJ/NOPB, the LM2651MTCX-ADJ delivers superior light-load efficiency and smallest total footprint due to fully integrated synchronous FETs and patented current sensing - making it optimal for space-constrained, battery-sensitive designs where 1.5-A output suffices.

Availability

LM2651MTCX-ADJ is available at Aetrix Electronics and suitable for personal digital assistants, handheld scanners, battery-powered medical devices, computer peripherals, and high-efficiency 5-V conversion systems requiring stable component supply and long-term production continuity.

Supply support for LM2651MTCX-ADJ 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 is a global semiconductor leader specializing in analog, embedded processing, and power management ICs, with decades of expertise in high-efficiency DC-DC conversion and automotive-grade reliability.

The LM2651 product line was designed specifically for portable and battery-operated applications demanding ultrahigh efficiency across ultra-wide load ranges - targeting PDA, scanner, and peripheral markets where standby current and thermal performance are critical.

FAQ

What is the feedback reference voltage for LM2651MTCX-ADJ?

The LM2651MTCX-ADJ uses a precision 1.238-V internal reference at the FB pin, with ±2.5% tolerance over temperature. This value is used in the resistor-divider equation V_OUT = 1.238 × (1 + R1/R2) to set the output voltage. Designers should select 1% metal-film resistors between 10 kΩ and 100 kΩ for optimal accuracy and noise immunity in the LM2651MTCX-ADJ application.

Does LM2651MTCX-ADJ require an external Schottky diode?

Yes - TI recommends adding an external Schottky diode (D1) across the low-side MOSFET's intrinsic body diode to prevent reverse-recovery losses and improve efficiency by 1–2%, especially at higher input voltages and loads. The LM2651MTCX-ADJ's datasheet specifies D1 placement adjacent to SW and PGND pins to minimize parasitic inductance and ensure reliable turn-on during deadtime.

What is the maximum duty cycle of LM2651MTCX-ADJ?

The LM2651MTCX-ADJ supports a maximum duty cycle of 92% at VIN = 4 V, enabling operation down to output voltages as low as ~0.37 V (4 V × 0.092). This high duty-cycle capability allows the LM2651MTCX-ADJ to maintain regulation in low-V_IN/V_OUT ratio applications such as 5-V-to-3.3-V or 12-V-to-5-V conversion without requiring additional stages.

How does LM2651MTCX-ADJ enter and exit sleep mode?

The LM2651MTCX-ADJ enters sleep (hysteretic) mode when load current falls below ~100 mA, causing output voltage to rise slightly and trigger the internal hysteretic comparator. It exits sleep mode when V_OUT drops to the lower hysteresis threshold (e.g., 24 mV for ADJ version), reactivating PWM control. This automatic transition is transparent to the user and requires no external control signals in the LM2651MTCX-ADJ design.

What thermal metrics apply to LM2651MTCX-ADJ in TSSOP package?

The LM2651MTCX-ADJ in 16-pin TSSOP has R_θJA = 97.3°C/W (no heatsink), R_θJC(top) = 29.9°C/W, and R_θJB = 43.1°C/W. These values assume standard JEDEC 2-layer board layout; thermal performance improves significantly with copper pour under the exposed pad (though not electrically connected). Derating begins at 7.14 mW/°C above 25°C ambient for the LM2651MTCX-ADJ.