Texas Instruments LP38859SX-1.2/NOPB

Overview

LP38859SX-1.2/NOPB from Texas Instruments is a 3-A, fast-response, high-accuracy LDO linear regulator with dual-rail operation (VIN and VBIAS), 1.2-V fixed output, 240-mV typical dropout at full load, ±1% output accuracy at 25°C, and programmable soft-start via external capacitor. It powers DSP/FPGA core rails and SMPS post-regulation in servers and graphics cards.

For engineers reviewing the LP38859SX-1.2/NOPB datasheet, LP38859SX-1.2/NOPB pinout, LP38859SX-1.2/NOPB application, or LP38859SX-1.2/NOPB equivalent, key selection factors include its ultra-low dropout under 3-A load, bias-supply independence (3–5.5 V), ceramic-capacitor stability (10 µF min), thermal shutdown (160°C), and soft-start timing control (r_SS = 16 kΩ).

Technical Context

The LP38859SX-1.2/NOPB uses an N-MOS pass transistor driven by a separate VBIAS rail (3–5.5 V), enabling stable regulation even when VIN approaches VOUT + 240 mV. Its CMOS architecture delivers low quiescent current (12 mA from VIN, 3.8 mA from VBIAS at 25°C) and wide bandwidth for fast transient response.

It integrates undervoltage lockout (UVLO threshold ≈2.45 V, 150-mV hysteresis), overcurrent protection (6.2-A short-circuit limit), and thermal shutdown (160°C, 10°C hysteresis). Soft-start is implemented via internal 16-kΩ resistor charging an external CSS capacitor, yielding controllable rise time (e.g., 800 µs with 10-nF CSS).

Key Specifications

Pinout & Package

LP38859SX-1.2/NOPB is housed in a 5-pin DDPAK/TO-263 package (10.16 mm × 8.42 mm) with exposed thermal tab electrically connected to GND. The tab serves as primary heat sink and must be soldered to a large copper pour for optimal thermal performance.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LP38859SX-1.2/NOPB, TPS7A8300RGRT offers lower dropout but no VBIAS flexibility, limiting ultra-low VIN use; LT3086EFE#PBF provides current sensing and higher temp rating but sacrifices 0.9 A of output current and adds external components - making LP38859SX-1.2/NOPB optimal for high-current, dual-rail, fixed-output server and FPGA applications.

Availability

LP38859SX-1.2/NOPB is available at Aetrix Electronics and suitable for server power delivery, FPGA core regulation, and SMPS post-regulation requiring stable component supply, long-term lifecycle support, and traceable sourcing for industrial and embedded OEM programs.

Supply support for LP38859SX-1.2/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 power solutions for industrial, automotive, and computing markets.

The LP38859 product line delivers high-current, low-dropout regulation with dual-rail architecture for demanding digital core and I/O supplies - designed specifically for next-generation servers, graphics accelerators, and reconfigurable logic platforms.

FAQ

What is the minimum input voltage required for LP38859SX-1.2/NOPB to regulate 1.2 V output?

The LP38859SX-1.2/NOPB requires VIN ≥ VOUT + VDO. With a typical dropout voltage of 240 mV at 3-A load, the minimum functional VIN is 1.44 V. However, the datasheet specifies absolute minimum VIN as 1.1 V - operation below 1.44 V results in unregulated output. Always verify actual dropout under your load and temperature conditions using the electrical characteristics table in the LP38859SX-1.2/NOPB datasheet.

Can LP38859SX-1.2/NOPB operate without a VBIAS supply?

No. LP38859SX-1.2/NOPB requires a valid VBIAS supply between 3 V and 5.5 V to power its internal control circuitry and drive the N-MOS pass transistor gate. If VBIAS falls below the UVLO threshold (~2.45 V), the device disables output regardless of VIN level. Leaving BIAS unconnected or shorted will prevent regulation - always connect a stable, bypassed 3–5.5-V source to the BIAS pin of LP38859SX-1.2/NOPB.

What is the purpose of the SS pin on LP38859SX-1.2/NOPB, and how is it configured?

The SS (soft-start) pin on LP38859SX-1.2/NOPB controls output voltage ramp rate via an external capacitor (CSS). An internal 16-kΩ resistor charges CSS, producing exponential VOUT rise. For LP38859SX-1.2/NOPB, typical r_SS = 16 kΩ yields 800 µs soft-start with 10-nF CSS. Connect CSS from SS to GND; leave SS open only if soft-start is intentionally disabled - though minimal capacitance is still recommended to reduce noise sensitivity.

Which output capacitors are compatible with LP38859SX-1.2/NOPB?

LP38859SX-1.2/NOPB is stable with ≥10-µF ceramic capacitors (X5R or X7R dielectrics) placed within 1 cm of the OUT pin and returned directly to the GND pin. Tantalum capacitors may be used in parallel but are not required. Avoid Z5U/Y5F ceramics due to capacitance loss over temperature. Aluminum electrolytics are discouraged below 0°C due to rising ESR. The LP38859SX-1.2/NOPB does not require ESR tuning - unlike older LDOs - thanks to its CMOS architecture.

Does LP38859SX-1.2/NOPB include built-in protection features?

Yes. LP38859SX-1.2/NOPB integrates overcurrent protection (6.2-A short-circuit limit), thermal shutdown (160°C junction, 10°C hysteresis), and undervoltage lockout (UVLO at ~2.45 V on VBIAS with 150-mV hysteresis). These protections are fully internal - no external components needed. Thermal shutdown is auto-recovering; current limit operates in foldback mode to minimize power dissipation during fault conditions. All protections are active across the full –40°C to +125°C operating range of LP38859SX-1.2/NOPB.