Texas Instruments LM2687LDX

Overview

LM2687LDX from Texas Instruments is a low-noise, regulated switched-capacitor voltage inverter IC that generates an adjustable negative output (−1.5V to −5.2V) from a +2.7V to +5.5V input supply. It delivers up to 10mA output current with 1mV typical output ripple, 91% typical charge-pump efficiency at 10mA, and operates at 100kHz switching frequency. It is used for GaAsFET power amplifier biasing in cellular handsets.

For engineers reviewing the LM2687LDX datasheet, LM2687LDX pinout, LM2687LDX application, or LM2687LDX equivalent, key selection criteria include its regulated negative output range, ultra-low shutdown current (0.05µA), MSOP-8/LLP-8 package compatibility, feedback-based voltage adjustment via VFB, and suitability for noise-sensitive RF bias applications.

Technical Context

The LM2687LDX integrates a fixed-frequency (100kHz typ.) switched-capacitor inverter stage followed by a low-dropout linear regulator. The charge-pump generates unregulated negative voltage at VNEG, which is then filtered and regulated at VOUT via internal LDO architecture with −1.20V feedback reference.

It uses external capacitors C1 (flyback), C2 (output smoothing), and C3 (LDO bypass) to define output resistance, ripple suppression, and transient response. Shutdown control (active-low SD) disconnects internal switches and grounds VOUT/VNEG, reducing quiescent current to 0.05µA.

Key Specifications

Pinout & Package

The LM2687LDX is housed in an 8-pin Leadless Leadframe Package (LLP-8, NS package code LDA08A), with exposed die attach pad (DAP) connected internally to VNEG for thermal and electrical performance.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar regulated negative voltage inverter applications.

Compared with MAX680ESA+ and TPS60403DBVR, the LM2687LDX uniquely combines ultra-low shutdown current (0.05µA), sub-millivolt ripple, and precise feedback-based regulation - making it optimal for battery-critical, noise-sensitive RF bias applications where long sleep duration and spectral purity are mandatory.

Availability

LM2687LDX is available at Aetrix Electronics and suitable for cellular phone power amplifier biasing, handheld instrumentation, and interface power supplies requiring stable component supply, consistent parametric performance, and long-term lifecycle support.

Supply support for LM2687LDX 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, signal chain, and high-reliability IC design.

The LM2687LDX belongs to TI's regulated charge-pump inverter product line, engineered specifically for low-noise, low-power negative voltage generation in portable wireless and instrumentation systems.

FAQ

What is the function of the VFB pin on the LM2687LDX?

The VFB pin on the LM2687LDX is the feedback input for the internal low-dropout linear regulator. It references a precise −1.20V internal voltage, enabling accurate output regulation via an external resistor divider between VOUT, VFB, and a stable reference (typically GND or VIN). This allows programmable output voltages from −1.5V to −5.2V without trimming components. The LM2687LDX relies on this pin to maintain regulation under varying load and input conditions.

Can the LM2687LDX operate from a 2.7V input supply?

Yes, the LM2687LDX is fully specified to operate from a minimum input voltage of +2.7V, delivering regulated negative output down to −1.5V (e.g., −1.5V at 2.7V input). At this rail, it maintains 10mA capability, 1mV ripple, and 91% efficiency per datasheet test conditions. The LM2687LDX is designed for single-cell Li-ion and low-voltage logic systems, ensuring robust functionality across the full 2.7V–5.5V input range.

What is the purpose of the DAP (Die Attach Pad) on the LM2687LDX LLP-8 package?

The DAP on the LM2687LDX LLP-8 package is an exposed thermal pad electrically connected to the VNEG pin. It must be soldered to a PCB copper pour tied to VNEG to improve thermal dissipation and reduce output noise by providing a low-inductance return path for charge-pump currents. Leaving the DAP unconnected degrades thermal performance and increases output ripple. The LM2687LDX datasheet explicitly requires DAP connection to VNEG for compliance with absolute maximum ratings.

How does shutdown affect the VOUT and VNEG pins of the LM2687LDX?

When the SD pin of the LM2687LDX is pulled low (≤0.5V), the device enters shutdown mode: internal switches disable, VOUT and VNEG are actively shorted to GND, and supply current drops to 0.05µA typical. This prevents reverse current flow and ensures zero output voltage during sleep. Upon exit from shutdown, the LM2687LDX resumes regulation with 120–600µs startup time depending on input voltage and capacitor values.

What capacitor types and values are recommended for the LM2687LDX?

The LM2687LDX requires three external capacitors: C1 (1µF flyback), C2 (1µF smoothing), and C3 (10µF LDO bypass), all with ≤0.3Ω ESR. Ceramic, surface-mount tantalum, or polymer electrolytic types are recommended. Larger values or lower-ESR capacitors further reduce output resistance and ripple. Using undersized or high-ESR capacitors increases dropout voltage, ripple, and reduces efficiency - directly impacting LM2687LDX performance in noise-critical applications.