Texas Instruments LP3856ESX-ADJ/NOPB

Overview

LP3856ESX-ADJ/NOPB from Texas Instruments is an adjustable ultra-low-dropout linear regulator delivering up to 3A DC output current with dropout as low as 39 mV at 300 mA and 390 mV at 3A. It operates from 2.5 V to 7.0 V input, features 1.216 V internal reference, 10 nA shutdown quiescent current, and supports ceramic or tantalum output capacitors. It serves as a primary post-regulator in microprocessor power supplies requiring fast transient response and tight load regulation (0.08%).

For engineers reviewing the LP3856ESX-ADJ/NOPB datasheet, LP3856ESX-ADJ/NOPB pinout, LP3856ESX-ADJ/NOPB application, or LP3856ESX-ADJ/NOPB equivalent, key selection considerations include dropout voltage vs. load, ADJ-pin bias current impact on resistor-divider accuracy, stability with ceramic COUT under varying ILOAD, thermal derating for TO-263 package, and reverse-current protection limits (200 mA continuous).

Technical Context

The LP3856ESX-ADJ/NOPB uses a PMOS pass element fabricated on a CMOS process, enabling low quiescent current independent of load and operation under ultra-low dropout conditions. Its feedback loop relies on a precision 1.216 V bandgap reference at the ADJ pin, with typical ADJ pin current of 10 nA-critical for minimizing resistor-divider error.

It integrates overtemperature and overcurrent protection, with short-circuit current limited to 6 A and thermal shutdown activating when junction temperature exceeds +125°C. Shutdown control is CMOS-compatible, with threshold voltages of 1.3 V (rising) and 0.3 V (falling), and requires active pull-up if driven by open-drain sources.

Key Specifications

Pinout & Package

LP3856ESX-ADJ/NOPB is packaged in DDPAK/TO-263-5 (surface-mount), with exposed thermal pad for enhanced heat dissipation. Thermal resistance θJA = 60°C/W with 0.5 in² 1 oz. copper area.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar adjustable LDO regulator applications.

Compared with TPS75733KTTT and LT1963AES8-ADJ, LP3856ESX-ADJ/NOPB uniquely combines ultra-low dropout (39 mV), adjustable output, TO-263 thermal capability, and 10 nA shutdown-making it optimal for high-efficiency, thermally demanding, programmable-rail applications where both precision and power density matter.

Availability

LP3856ESX-ADJ/NOPB is available at Aetrix Electronics and suitable for microprocessor power supplies, GTL bus terminators, DSP power management, SCSI active termination, and battery-charger reference rails requiring stable component supply across industrial temperature ranges and long production lifecycles.

Supply support for LP3856ESX-ADJ/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 designing analog, embedded processing, and connectivity technologies for industrial, automotive, and communications markets.

The LP3856ESX-ADJ/NOPB belongs to TI's ultra-low-dropout linear regulator family, engineered specifically for high-current, low-voltage digital systems where fast transient response, minimal dropout, and thermal robustness are mandatory.

FAQ

What is the minimum input voltage required for LP3856ESX-ADJ/NOPB to regulate a 1.5 V output?

The minimum input voltage is the greater of [VOUT(NOM) + VDROPOUT] or 2.5 V. For 1.5 V output, dropout is not specified below 2.5 V output per datasheet Section 4.4; thus, LP3856ESX-ADJ/NOPB is not characterized for 1.5 V operation. Valid outputs start at 1.216 V (reference), but full specs apply only at ≥2.5 V. Use LP3856ESX-ADJ/NOPB only for VOUT ≥2.5 V to ensure guaranteed dropout, line/load regulation, and thermal performance.

Can LP3856ESX-ADJ/NOPB use all-ceramic input and output capacitors?

Yes-LP3856ESX-ADJ/NOPB supports all-ceramic designs, but COUT must be ≤500 µF when CIN = 10 µF and ILOAD = 1 A (per Figure 26). At 3 A load, CIN and COUT must be nearly equal (≈1:1 ratio) for stability. X5R/X7R dielectrics are mandatory; Z5U/Y5V are prohibited due to severe capacitance loss with voltage/temperature. Always verify stability with actual layout and worst-case ESR/temperature.

How does the ADJ pin bias current affect output voltage accuracy in LP3856ESX-ADJ/NOPB?

LP3856ESX-ADJ/NOPB ADJ pin draws 10 nA (typ), flowing through R2 in the feedback divider. With R2 = 10 kΩ, this adds ~0.1 mV error-negligible. But with R2 = 1 MΩ, error rises to ~10 mV, degrading accuracy. To hold total error <1%, use R1 + R2 ≤ 200 kΩ and 1% resistors. The LP3856ESX-ADJ/NOPB datasheet explicitly warns against R1 > 100 kΩ for precision applications.

What is the maximum continuous reverse current the LP3856ESX-ADJ/NOPB can tolerate from VOUT to VIN?

LP3856ESX-ADJ/NOPB contains a parasitic body diode between VIN and VOUT. When VOUT > VIN, this diode conducts. The device tolerates 200 mA continuous reverse current and 1 A peak (per Absolute Maximum Ratings, Section 6.5). Exceeding 200 mA risks thermal overstress or latch-up. External reverse-blocking diodes are recommended in applications prone to output voltage overshoot or backup power scenarios.

Does LP3856ESX-ADJ/NOPB require a feed-forward capacitor (CFF), and how is it calculated?

Yes-CFF is required for phase compensation. Its value depends on R1: Fz = 45 kHz = 1/(2π × R1 × CFF). For R1 = 100 kΩ, CFF ≈ 35 pF. Use X5R/X7R ceramic; place close to ADJ and VOUT pins. Omitting CFF causes instability with ceramic COUT, especially at high load currents. The LP3856ESX-ADJ/NOPB Application Hints (Section 9.1) mandate CFF for all designs using R1 > 10 kΩ.