Texas Instruments LP3855ESX-3.3/NOPB

Overview

LP3855ESX-3.3/NOPB from Texas Instruments is a fixed-output, ultra-low dropout linear regulator delivering 3.3 V ±1.5% at up to 1.5 A DC, with 240 mV dropout at full load, CMOS-based low-quiescent-current operation (4 mA typical), and remote-sense capability via dedicated SENSE pin for improved load regulation in distributed power systems.

For engineers reviewing the LP3855ESX-3.3/NOPB datasheet, LP3855ESX-3.3/NOPB pinout, LP3855ESX-3.3/NOPB application, or LP3855ESX-3.3/NOPB equivalent, key selection considerations include dropout performance under 1.5-A load, ceramic capacitor stability support, shutdown control timing (25 µs turn-on delay), thermal derating in SOT-223 package, and remote-sense implementation for point-of-load accuracy.

Technical Context

The LP3855ESX-3.3/NOPB uses a PMOS pass element on a CMOS process enabling load-independent quiescent current and ultra-low dropout-240 mV at 1.5 A and 26 mV at 150 mA. Its SENSE pin provides feedback directly at the remote load, decoupling output regulation from PCB trace resistance.

It features active overtemperature and overcurrent protection, 10-nA shutdown current, and an open-drain ERROR flag (not present on LP3855) - though LP3855ESX-3.3/NOPB omits ERROR in favor of SENSE. Shutdown is controlled by a logic-level SD input with 1.3–2.0 V threshold and no hysteresis.

Key Specifications

Pinout & Package

SOT-223 (NDC) package: 6.50 mm × 3.56 mm body, thermally enhanced with exposed pad (not electrically connected); designed for surface-mount assembly and moderate power dissipation without heatsink.

Key Features

Applications

Equivalent & Alternatives

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

Compared with TSS721AIDR and TPS7A4700RGWR, LP3855ESX-3.3/NOPB uniquely combines fixed 3.3-V output, 1.5-A capability, SENSE-based remote regulation, and sub-250-mV dropout - making it the only option among the three qualified for high-current, distributed-point-of-load applications demanding both accuracy and layout robustness.

Availability

LP3855ESX-3.3/NOPB is available at Aetrix Electronics and suitable for microprocessor power supplies, GTL/SSTL bus terminators, and battery-powered portable devices requiring stable component supply, long-term lifecycle assurance, and consistent parametric performance across production batches.

Supply support for LP3855ESX-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 is a global semiconductor leader specializing in analog, embedded processing, and power management ICs, with decades of expertise in high-reliability linear regulation and power system design.

The LP3855 series was developed specifically for low-voltage, high-current microprocessor and digital interface applications requiring ultra-low dropout, fast transient response, and remote-sense accuracy - targeting FPGA, DSP, and memory subsystem power delivery.

FAQ

What is the minimum input voltage required for LP3855ESX-3.3/NOPB to regulate 3.3 V at 1.5 A?

The LP3855ESX-3.3/NOPB requires a minimum input voltage of 3.54 V (3.3 V + 240 mV dropout) to maintain regulation at 1.5 A load. At lighter loads, dropout decreases - e.g., 26 mV at 150 mA - allowing operation down to ~3.33 V. Input must also meet absolute minimum of 2.5 V per datasheet operating conditions.

Can LP3855ESX-3.3/NOPB be used with only ceramic capacitors, and what are the stability limits?

Yes, LP3855ESX-3.3/NOPB is stable with ceramic output capacitors ≥10 µF. With a 10-µF ceramic input capacitor and 1.5-A load, maximum stable ceramic C_OUT is ~150 µF (per Figure 21). Exceeding this risks oscillation; total ceramic capacitance at the output - including bypass caps - must stay within the limit.

How should the SENSE pin be connected in a typical LP3855ESX-3.3/NOPB application?

In LP3855ESX-3.3/NOPB, the SENSE pin must be connected directly to the load's VCC pin using a dedicated, low-impedance trace - not to the OUT pin. If remote sensing is unused, SENSE must be tied to OUT. Never leave SENSE floating, as it will degrade regulation accuracy and may cause instability.

Does LP3855ESX-3.3/NOPB include an ERROR flag output like the LP3852?

No. LP3855ESX-3.3/NOPB does not have an ERROR pin; that function is exclusive to the LP3852 family. The LP3855 replaces ERROR with the SENSE pin. Therefore, LP3855ESX-3.3/NOPB provides no output fault indication - system-level monitoring must be implemented externally if required.

What thermal derating applies to LP3855ESX-3.3/NOPB in the SOT-223 package?

In SOT-223 (NDC), LP3855ESX-3.3/NOPB has R_θJA = 65.2°C/W (with 0.5 in², 1-oz copper). At 25°C ambient and 1.5-A load with 3.54-V input, power dissipation is ~360 mW, resulting in ~58°C junction rise - well within the −40°C to 125°C rating. Higher ambient or reduced copper area requires proportional current derating.