Texas Instruments LM2677S-ADJ

Overview

LM2677S-ADJ from Texas Instruments is a monolithic step-down (buck) DC-DC switching regulator with integrated 100-mΩ DMOS power switch, delivering up to 5 A output current across an adjustable output range of 1.2 V to 37 V. It operates from 8 V to 40 V input, achieves up to 92% efficiency, and supports external synchronization from 280 kHz to 400 kHz - used in high-current industrial power supplies and battery-charged systems requiring stable, low-quiescent regulation.

For engineers reviewing the LM2677S-ADJ datasheet, LM2677S-ADJ pinout, LM2677S-ADJ application, or LM2677S-ADJ equivalent, key selection criteria include its ±2% output voltage tolerance over line/load/temperature, 50-μA standby current in shutdown mode, internal 260-kHz oscillator, thermal shutdown protection, and ON/OFF enable control with 1.4-V threshold.

Technical Context

The LM2677S-ADJ implements a fixed-frequency PWM buck controller with internal 260-kHz oscillator or externally synchronized operation (280–400 kHz), enabling precise ripple frequency control for EMI-sensitive applications like radio equipment. Its feedback loop uses a two-stage high-gain amplifier referenced to a 1.21-V internal bandgap, supporting resistor-divider programming for output voltages from 1.2 V to 37 V.

It integrates thermal shutdown, cycle-by-cycle current limiting (6.1–8.75 A over temperature), and a bootstrap-driven high-side MOSFET gate driver requiring a 0.01-μF CB capacitor. The device enters 50-μA standby mode when the ON/OFF pin is pulled below 0.8 V, and features 0.12–0.225-Ω R_DS(ON) over –40°C to 125°C junction temperature.

Key Specifications

Pinout & Package

LM2677S-ADJ is available in TO-263 (KTW), TO-220 (NDZ), and VSON (NHM) packages. The S-suffix denotes surface-mount TO-263-7 (DDPAK) variant with exposed thermal pad (DAP) for enhanced thermal performance.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LM2677S-ADJ, LM2678-ADJ offers identical interface and layout but reduced current capability, while TPS54560B provides greater flexibility in frequency and control features at the cost of different pinout and compensation requirements.

Availability

LM2677S-ADJ is available at Aetrix Electronics and suitable for industrial power supplies, battery charging systems, communications equipment, and ruggedized embedded systems requiring stable component supply across long product lifecycles.

Supply support for LM2677S-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 company specializing in analog and embedded processing technologies, with leadership in power management ICs for industrial, automotive, and communications markets.

The LM2677 series belongs to TI's SIMPLE SWITCHER® family - designed to simplify high-efficiency DC-DC buck converter implementation using minimal external components and standardized magnetics.

FAQ

What is the minimum input voltage required for stable operation of the LM2677S-ADJ?

The LM2677S-ADJ requires a minimum input voltage of 8 V to maintain regulation across its full output range and load conditions. Below this threshold, the internal control circuitry cannot sustain proper gate drive or feedback loop stability. This specification is validated over –40°C to 125°C junction temperature and applies regardless of output voltage setting or external sync usage. Always verify input source compliance with this limit in battery-fed or unregulated supply designs involving LM2677S-ADJ.

How does the SYNC pin affect current limiting behavior in the LM2677S-ADJ?

When the SYNC pin is actively driven with an external clock signal (280–400 kHz), current-limit frequency foldback is disabled in the LM2677S-ADJ. As a result, the device maintains full current-limit threshold (6.1–8.75 A) without reduction during overload, but loses dynamic adjustment under sustained short-circuit conditions. This behavior is documented in Section 7.3.4 of the LM2677S-ADJ datasheet and must be accounted for in fault-tolerant designs. For applications requiring robust short-circuit protection with SYNC enabled, external current sensing or secondary protection is recommended alongside LM2677S-ADJ.

What is the recommended bootstrap capacitor value for the LM2677S-ADJ CB pin?

The LM2677S-ADJ datasheet specifies a 0.01-μF (10 nF) ceramic capacitor for the CB pin, connected between CB and VSW. This value ensures sufficient charge transfer to fully enhance the internal high-side DMOS FET gate above VIN, minimizing conduction losses and maintaining >90% efficiency. X7R or C0G dielectrics are preferred for stable capacitance across temperature and bias. Larger values do not improve performance and may slow startup; smaller values risk insufficient gate drive under heavy load or high ambient temperature. This requirement applies identically across all LM2677S-ADJ package variants.

Can the LM2677S-ADJ operate without an external feedback resistor divider?

No - the LM2677S-ADJ is the adjustable-output version and requires an external resistor divider connected between VOUT, FB, and GND to set the output voltage. Unlike fixed-output variants (e.g., LM2677-5.0), it contains no internal feedback resistors. The FB pin senses the divider midpoint and regulates to 1.21 V, so V_OUT = 1.21 × (1 + R1/R2). Omitting the divider results in undefined or non-regulated output. This configuration is mandatory for all LM2677S-ADJ applications and is confirmed in Section 6.8 and Figure 8 of the official datasheet.

What thermal considerations apply to the LM2677S-ADJ in TO-263 (KTW) package?

The LM2677S-ADJ in TO-263 (KTW) package has a junction-to-ambient thermal resistance (R_θJA) ranging from 26°C/W (with 7.4× package copper area) to 56°C/W (minimal copper), per Section 6.4 of the datasheet. Effective thermal design requires soldering the exposed thermal pad (DAP) directly to a large internal or bottom-side ground plane with ≥4 thermal vias. Without adequate copper, junction temperature can exceed 125°C at 5-A load even at 25°C ambient. TI recommends verifying thermal performance using the measured R_θJA value corresponding to actual PCB layout when designing with LM2677S-ADJ.