Texas Instruments LP38858SX-1.2/NOPB

Overview

LP38858SX-1.2/NOPB from Texas Instruments is a 1.5A fast-response, high-accuracy LDO linear regulator with dual-rail operation (VIN for power path, VBIAS for control circuitry), 1.2V fixed output, 130 mV typical dropout at full load, ±2.0% output accuracy over 0°C to +125°C, and stable operation with 10 µF ceramic output capacitance - used in FPGA core voltage regulation and SMPS post-regulation.

For engineers reviewing the LP38858SX-1.2/NOPB datasheet, LP38858SX-1.2/NOPB pinout, LP38858SX-1.2/NOPB application, or LP38858SX-1.2/NOPB equivalent, key selection considerations include its dual-supply architecture (VIN/VBIAS), soft-start programmability via CSS, ultra-low ground current (3.8 mA from VBIAS), thermal shutdown at 160°C, and compatibility with low-ESR ceramic capacitors without external compensation.

Technical Context

The LP38858SX-1.2/NOPB employs an N-MOS pass transistor driven by a separate VBIAS rail (3.0–5.5V), enabling ultra-low VIN operation down to VOUT + VDO. Its CMOS-based control loop delivers fast transient response and operates stably with only 10 µF ceramic COUT.

Soft-start is implemented via internal 16.0 kΩ SS-pin resistance (rSS) and external CSS capacitor, yielding programmable startup time (e.g., 800 µs with 10 nF). Under-voltage lockout activates below ~2.45V on VBIAS with 150 mV hysteresis, ensuring controlled enable/disable sequencing.

Key Specifications

Pinout & Package

LP38858SX-1.2/NOPB uses the DDPAK/TO-263 (KTT0005B) 5-lead package with exposed thermal tab soldered to PCB copper plane for enhanced heat dissipation (θJC = 3°C/W).

Key Features

Applications

Equivalent & Alternatives

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

Compared with TPS7A8300RGRT and LT3045EMSE#PBF, LP38858SX-1.2/NOPB uniquely combines 1.5A capability, dual-rail operation, programmable soft-start, and thermal protection - making it optimal for high-current, thermally constrained digital core regulation where VIN may approach VOUT.

Availability

LP38858SX-1.2/NOPB is available at Aetrix Electronics and suitable for FPGA power delivery, server I/O regulation, and industrial DSP core supplies requiring stable component supply, long-term lifecycle support, and RoHS-exempt packaging for legacy manufacturing.

Supply support for LP38858SX-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 linear regulators and power solutions.

The LP38858 product line was designed specifically for high-current, fast-transient digital core regulation in computing and communications infrastructure - emphasizing dual-rail efficiency, ceramic capacitor compatibility, and thermal robustness.

FAQ

What is the minimum input voltage required for LP38858SX-1.2/NOPB to regulate at full 1.5A?

The LP38858SX-1.2/NOPB requires VIN ≥ VOUT + VDO = 1.2V + 0.13V = 1.33V (typical) at 1.5A load. However, VIN must also remain ≤ VBIAS, and VBIAS must be maintained between 3.0V and 5.5V. Therefore, the practical minimum VIN is 1.33V, provided VBIAS is independently supplied within spec. The device will not regulate if VIN falls below this threshold under load.

Can LP38858SX-1.2/NOPB operate without a soft-start capacitor?

Yes, LP38858SX-1.2/NOPB can operate with the SS pin left open - the soft-start function is optional. However, omitting CSS removes inrush current limiting, potentially causing large output voltage overshoot or triggering upstream current-limit protection during startup. For reliable system behavior, TI recommends using at least 1 nF; the LP38858SX-1.2/NOPB datasheet specifies 10 nF for ~800 µs controlled rise time.

What is the maximum allowable PCB copper area for thermal performance of LP38858SX-1.2/NOPB?

LP38858SX-1.2/NOPB uses the DDPAK/TO-263 (KTT) package with a thermal tab that must be soldered to PCB copper. Per TI's Figure 28, increasing copper area beyond 1 square inch yields diminishing returns; the minimum achievable θJA is ~32°C/W. No upper limit exists - larger copper planes improve thermal performance, but mechanical clearance and layer stackup constraints typically govern practical implementation.

Does LP38858SX-1.2/NOPB require specific capacitor dielectrics for stability?

Yes, LP38858SX-1.2/NOPB requires X5R or X7R ceramic capacitors for CIN and COUT (minimum 10 µF each) to ensure stability across temperature. Z5U and Y5F types are explicitly excluded due to insufficient capacitance retention at temperature extremes. CBIAS (≥1 µF) also benefits from X5R/X7R, though other high-quality ceramics are acceptable per TI's Application Information section.

How does the VBIAS undervoltage lockout (UVLO) behave during power-down sequencing?

LP38858SX-1.2/NOPB features a VBIAS UVLO threshold of ~2.45V with 150 mV hysteresis. When VBIAS falls below 2.45V, the device disables output and actively discharges CSS until VBIAS drops to ~500 mV. This ensures clean, monotonic shutdown and prevents erratic behavior during brownout conditions - critical for systems requiring deterministic power sequencing in server or telecom applications.