Texas Instruments LP38691SDX-1.8

Overview

LP38691SDX-1.8 from Texas Instruments is a 500-mA, 1.8-V fixed-output low-dropout CMOS linear regulator in WSON-6 package with PMOS pass transistor, 250 mV dropout at 500 mA (V_OUT = 5 V), ±2% output accuracy over –40°C to 125°C, and stable operation with 1-µF ceramic output capacitor. It serves as a primary voltage rail for microcontroller core supplies in portable instrumentation.

For engineers reviewing the LP38691SDX-1.8 datasheet, LP38691SDX-1.8 pinout, LP38691SDX-1.8 application, or LP38691SDX-1.8 equivalent, key selection considerations include dropout voltage at 1.8 V output, ground pin current under full load, thermal performance in WSON-6, and compatibility with ultra-low-ESR ceramic capacitors without external compensation.

Technical Context

The LP38691SDX-1.8 uses a precision trimmed bandgap reference and PMOS pass element, eliminating DC base-drive current and maintaining ground pin current ≤55 µA across load, input voltage, and temperature. Its internal foldback current limiting activates based on VIN–VOUT differential: ~350 mA limit when ΔV > 5 V, ~850 mA when ΔV < 4 V.

No enable pin is present-unlike LP38693-so regulation is always active when VIN ≥ 2.7 V and ≥ (VOUT + VDO). Thermal shutdown triggers at ~160°C junction temperature with ~10°C hysteresis, and remote sense (SNS) is available only on WSON variants for load-side voltage correction.

Key Specifications

Pinout & Package

LP38691SDX-1.8 is housed in a 3.0 mm × 3.0 mm WSON-6 package with exposed thermal pad (DAP) on bottom for enhanced heat dissipation. The DAP must be soldered to a PCB copper plane per TI AN-1187 for thermal compliance.

Key Features

Applications

Equivalent & Alternatives

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

Compared with TPL7407LPGQ and TPS7A0518PDBVR, LP38691SDX-1.8 uniquely delivers 500-mA capability with remote sensing, 1.8-V precision, and WSON thermal performance-making it the only viable option for high-fidelity 1.8-V power delivery in compact industrial and portable systems.

Availability

LP38691SDX-1.8 is available at Aetrix Electronics and suitable for hard disk drives, notebook computers, and battery-powered medical sensors requiring stable component supply, long-term lifecycle support, and guaranteed traceability.

Supply support for LP38691SDX-1.8 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 company headquartered in Dallas, Texas, designing and manufacturing analog and embedded processing chips for industrial, automotive, and personal electronics markets.

The LP3869x family was developed specifically for portable, battery-powered digital systems requiring fast start-up, tight output tolerance, and stable operation with miniature ceramic capacitors-targeting space- and efficiency-constrained applications.

FAQ

What is the maximum input voltage rating for LP38691SDX-1.8?

The absolute maximum input voltage for LP38691SDX-1.8 is 12 V, but the recommended operating range is 2.7 V to 10 V. Exceeding 10 V may degrade long-term reliability even if within absolute max limits, and operation below 2.7 V prevents regulation. LP38691SDX-1.8 requires VIN ≥ (1.8 V + V_DO) to maintain output regulation-typically ≥1.9 V at light load and ≥2.0 V at 500 mA.

Does LP38691SDX-1.8 include an enable pin?

No, LP38691SDX-1.8 does not have an enable (EN) pin. Unlike the LP38693 variant, the LP38691 series operates continuously whenever VIN is within specification. To disable output, VIN must be removed or dropped below 2.7 V. This simplifies design in always-on applications but removes software-controlled power gating capability-confirm LP38691SDX-1.8 is appropriate before selecting for systems requiring dynamic enable control.

Can LP38691SDX-1.8 be used with a 1-µF output capacitor?

Yes, LP38691SDX-1.8 is explicitly designed and characterized for stability with a single 1-µF ceramic output capacitor-no additional ESR or capacitance is required. This is enabled by its CMOS architecture and internal compensation. Using larger values (e.g., 10 µF) is acceptable and may improve transient response, but the 1-µF minimum ensures robustness in size- and cost-sensitive layouts. LP38691SDX-1.8 achieves this without external components, unlike many older LDOs requiring 10–22 µF tantalum caps.

What is the purpose of the SNS pin on LP38691SDX-1.8?

The SNS (sense) pin on LP38691SDX-1.8 enables remote voltage sensing at the load to compensate for IR drop in PCB traces between the regulator and target IC. It must be connected directly to the load-side VOUT node-not the regulator's OUT pin-to improve regulation accuracy at the point-of-load. This feature is exclusive to WSON-package LP38691 devices and is inactive if left floating or tied to GND. LP38691SDX-1.8 achieves ±2% output accuracy at the load using SNS, versus ±4% without it under worst-case trace resistance.

How does thermal performance of LP38691SDX-1.8 compare across packages?

LP38691SDX-1.8 is only offered in the WSON-6 package, which provides R_θJA = 50.6°C/W (high-K board) and R_θJB = 24.9°C/W-superior to SOT-223 (R_θJA = 68.5°C/W) and comparable to TO-252 (R_θJA = 50.5°C/W). Its exposed thermal pad (DAP) must be soldered to ≥4 thermal vias connected to an inner ground plane to achieve published thermal metrics. Without proper DAP layout, junction temperature rise increases significantly-potentially triggering thermal shutdown at <300 mA under 60°C ambient.