Texas Instruments LP3891ESX-1.5/NOPB

Overview

LP3891ESX-1.5/NOPB from Texas Instruments is a 0.8A ultra-low-dropout linear regulator with CMOS N-MOS pass transistor architecture, delivering 1.5V fixed output at ≤100mV dropout (typ, 0.8A), ±1.5% output accuracy (25°C), and 60nA shutdown current - designed for post-regulation in DSP, microcontroller core, and server I/O power supplies.

For engineers reviewing the LP3891ESX-1.5/NOPB datasheet, LP3891ESX-1.5/NOPB pinout, LP3891ESX-1.5/NOPB application, or LP3891ESX-1.5/NOPB equivalent, key selection factors include its dual-rail operation (VIN + VBIAS), bias-supply-dependent thermal shutdown, SO PowerPAD-8 package thermal performance, and strict ESR-stability requirements for 10µF tantalum output capacitors.

Technical Context

The LP3891ESX-1.5/NOPB uses an external VBIAS rail (4.5–6V) to drive the gate of its N-MOS pass transistor, enabling stable regulation even when VIN approaches VOUT - unlike bipolar LDOs, this architecture sustains <3mA ground current across full 0–0.8A load range. Its control loop requires no compensation and achieves fast transient response via wide bandwidth inherent to the N-MOS topology.

Stability relies on ≥10µF output capacitance with ESR between 0.001Ω and 1Ω (per Figure 18), mandating tantalum or specific aluminum electrolytics; ceramic capacitors alone are unstable due to sub-10mΩ ESR. Shutdown is controlled by the S/D pin, which must be actively pulled up (10–100kΩ) and asserts <0.3V threshold to disable output within 20µs.

Key Specifications

Pinout & Package

LP3891ESX-1.5/NOPB is packaged in DDPAK/TO-263 (KTT), a 5-pin surface-mount power package with exposed thermal pad soldered to PCB copper for θJA ≈ 40°C/W (1.5 in² copper plane). Pin 1 is marked by notch or dot; leads are gull-wing, RoHS-exempt, MSL Level-3 (245°C peak reflow).

Key Features

Applications

Equivalent & Alternatives

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

Compared with LP3891ESX-1.5/NOPB, TPS7A4701RGWR offers lower noise but forfeits ultra-low-VIN capability, while MCP1826T-1502E/DB trades dropout and protection for footprint and cost - making LP3891ESX-1.5/NOPB optimal for thermally constrained, multi-rail industrial designs demanding <100mV dropout and −40°C to +125°C operation.

Availability

LP3891ESX-1.5/NOPB is available at Aetrix Electronics and suitable for server I/O power, DSP core supply, and SMPS post-regulation applications requiring stable component supply, long-term lifecycle support, and traceable sourcing for industrial and telecom deployments.

Supply support for LP3891ESX-1.5/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 regulators and power solutions.

The LP3891 series was engineered for high-current, ultra-low-dropout applications in DSP, microcontroller, and server power domains - emphasizing thermal robustness, dual-supply flexibility, and stability with minimal external components.

FAQ

What is the minimum input voltage required for LP3891ESX-1.5/NOPB to regulate 1.5V output?

The LP3891ESX-1.5/NOPB requires VIN ≥ (VOUT + VDO), where typical dropout is 100mV at 0.8A. Thus, minimum VIN is 1.6V under full load. However, VBIAS must also be present (4.5–6V) to enable gate drive - VIN alone cannot sustain regulation without VBIAS. Below 1.6V, output collapses proportionally.

Can LP3891ESX-1.5/NOPB operate without the VBIAS supply?

No. LP3891ESX-1.5/NOPB requires an external 4.5–6V VBIAS rail to drive the N-MOS pass transistor gate. Without VBIAS, the device remains in under-voltage lockout (UVLO) and delivers no output, regardless of VIN level. The VBIAS pin must not be left floating or tied to VIN.

What output capacitor types are validated for stable operation with LP3891ESX-1.5/NOPB?

Tantalum capacitors are explicitly recommended for LP3891ESX-1.5/NOPB output due to their stable ESR (0.001–1Ω) across temperature. Aluminum electrolytics may be used only if rated for ≥10°C operation and specified ESR at ≥100kHz. Ceramic capacitors alone cause instability; up to 15% ceramic can supplement tantalum but not replace it.

How does the S/D pin function on LP3891ESX-1.5/NOPB, and what pull-up value is required?

The S/D pin is an active-low shutdown input. It must be pulled up to VBIAS (or VIN) via 10–100kΩ resistor for normal operation. Driving S/D <0.3V disables output within 20µs and reduces quiescent current to 60nA. If driven by rail-to-rail CMOS logic, the pull-up resistor is optional.

What thermal design considerations apply to LP3891ESX-1.5/NOPB in DDPAK/TO-263 package?

LP3891ESX-1.5/NOPB in DDPAK/TO-263 achieves θJA ≈ 40°C/W when soldered to ≥1.5 in² copper plane. Power dissipation PD = (VIN−1.5V)×IOUT + VIN×IGND must keep junction temperature ≤125°C. For 0.8A at VIN=2.5V, PD ≈ 0.8W - requiring ≥1.5 in² copper or forced air if ambient exceeds 85°C.