Texas Instruments LP3855ESX-1.8/NOPB

Overview

LP3855ESX-1.8/NOPB from Texas Instruments is a fixed-output 1.8 V, 1.5 A ultra-low dropout linear regulator in TO-263-5 (DDPAK) package, featuring 24 mV dropout at 150 mA and 240 mV at 1.5 A, ±1.5% output voltage accuracy at 25°C, and remote sense capability for improved load regulation in microprocessor power supplies.

For engineers reviewing the LP3855ESX-1.8/NOPB datasheet, LP3855ESX-1.8/NOPB pinout, LP3855ESX-1.8/NOPB application, or LP3855ESX-1.8/NOPB equivalent, key selection considerations include dropout performance under full load, SENSE pin implementation for remote load regulation, shutdown quiescent current (10 nA), thermal derating in TO-263 package, and compatibility with ceramic or tantalum output capacitors ≥10 µF.

Technical Context

The LP3855ESX-1.8/NOPB uses a CMOS-based PMOS pass element enabling load-independent quiescent current (4 mA typical at 1.5 A) and ultra-low dropout operation. Its SENSE pin provides feedback from the remote load point, decoupling regulation from PCB trace resistance-critical for maintaining 1.8 V ±3% at high-current digital loads.

It integrates overtemperature and overcurrent protection, features an active-low shutdown input requiring external 10-kΩ pull-up, and delivers fast transient response due to high bandwidth error amplifier architecture-verified by 1-A load step tests showing <100 mV undershoot/overshoot with 2×10 µF ceramic output capacitance.

Key Specifications

Pinout & Package

LP3855ESX-1.8/NOPB is housed in a thermally enhanced DDPAK/TO-263-5 (KTT) package (10.16 mm × 8.42 mm), with exposed thermal pad for PCB heat sinking. Pin 1 = SD (shutdown input), Pin 2 = IN (input supply), Pin 3 = OUT (regulated output), Pin 4 = SENSE (remote voltage sense), Pin 5 = GND (power ground).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar ultra-low dropout linear regulator applications.

Compared with TPS7A4700RGWR and LP3878SD-1.8, LP3855ESX-1.8/NOPB uniquely balances 1.5 A output, remote sensing, and TO-263 thermal performance-making it the only option among the three capable of maintaining 1.8 V ±3% at a 1.5 A remote load over −40°C to 125°C.

Availability

LP3855ESX-1.8/NOPB is available at Aetrix Electronics and suitable for microprocessor core supplies, GTL+ bus terminators, and battery-powered DSP systems requiring stable component supply, long-term manufacturability, and automotive-grade temperature support.

Supply support for LP3855ESX-1.8/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 is a global semiconductor company designing analog ICs, embedded processors, and power management solutions for industrial, automotive, and communications markets.

The LP3855ESX-1.8/NOPB belongs to TI's LP385x ultra-low dropout linear regulator product line, engineered specifically for high-current, low-voltage microprocessor and DSP power delivery where remote sensing and fast transient response are essential.

FAQ

What is the minimum input voltage required for LP3855ESX-1.8/NOPB to regulate 1.8 V at 1.5 A?

The LP3855ESX-1.8/NOPB requires a minimum input voltage of 2.04 V (1.8 V + 240 mV dropout) to maintain regulation at 1.5 A. Per datasheet Section 8.5, dropout is specified as 240 mV typical at 1.5 A for TO-263 devices. Input below this threshold causes output to droop proportionally; the absolute minimum operating VIN is 2.5 V per Recommended Operating Conditions, but functional regulation begins at VOUT + V_DROPOUT.

How should the SENSE pin be connected if remote load regulation is not needed for LP3855ESX-1.8/NOPB?

If remote load regulation is not required, the SENSE pin of LP3855ESX-1.8/NOPB must be connected directly to the OUT pin-never left floating. This configuration ensures the feedback loop regulates at the device's output terminal, matching standard LDO behavior. Leaving SENSE unconnected risks instability or incorrect regulation, as confirmed in Section 9.3.1 and Figure 16 of the SNVS174I datasheet.

Can LP3855ESX-1.8/NOPB operate stably with only ceramic capacitors, and what are the limits?

Yes, LP3855ESX-1.8/NOPB operates stably with ceramic capacitors. Minimum C_OUT is 10 µF; maximum stable ceramic C_OUT depends on C_IN-e.g., with 10 µF ceramic C_IN, C_OUT may be up to ~150 µF at 1.5 A (per Figure 21). Exceeding this limit risks oscillation. Tantalum is also supported, and mixed dielectrics are acceptable if total C_OUT ≥10 µF and ESR stays within stable region.

What is the thermal performance of LP3855ESX-1.8/NOPB in its TO-263 package, and how does it affect maximum load?

LP3855ESX-1.8/NOPB in TO-263 (KTT) has R_θJA = 40.3°C/W (with 0.5 in², 1-oz copper). At 1.5 A and 2.04 V dropout, power dissipation is 0.36 W, yielding ~14.5°C rise above ambient. Full 1.5 A is sustainable up to ~110°C ambient with proper PCB copper area; derating is required above that. Thermal metrics are detailed in Section 8.4 of SNVS174I.

Does LP3855ESX-1.8/NOPB include reverse current protection, and what are the limits?

LP3855ESX-1.8/NOPB does not include active reverse current protection. Its internal PMOS pass device contains a parasitic body diode that conducts if V_OUT > V_IN. Per Section 9.3.4, this diode tolerates 200 mA continuous and 1 A peak reverse current. External reverse-blocking circuitry (e.g., series Schottky) is required in back-drive scenarios such as hot-swap or multi-rail systems.