Texas Instruments LP38691QSD-1.8/NOPB

Overview

LP38691QSD-1.8/NOPB from Texas Instruments is a 500-mA, 1.8-V fixed-output CMOS low-dropout linear regulator in a 6-pin WSON package with exposed thermal pad. It features 2% output accuracy at 25°C, 250 mV typical dropout at 500 mA (V_OUT = 5 V), stable operation with 1-µF ceramic output capacitors, and operates across 2.7 V to 10 V input range. It delivers precise voltage regulation for microcontroller core supplies in portable instrumentation.

For engineers reviewing the LP38691QSD-1.8/NOPB datasheet, LP38691QSD-1.8/NOPB pinout, LP38691QSD-1.8/NOPB application, or LP38691QSD-1.8/NOPB equivalent, key selection considerations include dropout voltage at 1.8 V output, ground pin current under full load, thermal performance in WSON-6, remote sense capability (SNS pin), and foldback current limiting behavior across input–output differentials.

Technical Context

The LP38691QSD-1.8/NOPB uses a PMOS pass transistor architecture enabling ultra-low ground pin current (55 µA typical at full load) independent of load, input voltage, or temperature. Its internal trimmed bandgap reference ensures 2% output tolerance over –40°C to 125°C, and it incorporates thermal shutdown (160°C activation, 10°C hysteresis) and foldback current limiting that scales load current based on VIN–VOUT differential (e.g., ~350 mA limit when ΔV > 5 V).

No enable pin is present-unlike the LP38693 variant-so the device operates continuously when powered. The SNS pin supports remote voltage sensing for precision regulation at the load, and the WSON-6 package includes an exposed thermal pad (DAP) soldered to PCB copper for enhanced thermal dissipation (R_θJB = 24.9°C/W).

Key Specifications

Pinout & Package

The LP38691QSD-1.8/NOPB is housed in a 6-pin WSON package (NGG) with 3.00 mm × 3.00 mm body size and an exposed thermal pad (DAP) on the bottom for PCB-level heat sinking.

Key Features

Applications

Equivalent & Alternatives

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

Compared with TPL7407LPGEDR and TPS7A0518PDBVR, the LP38691QSD-1.8/NOPB uniquely supports 500-mA continuous output with remote sensing and foldback protection-making it the only option among the three capable of precision, high-current regulation in thermally demanding portable instrumentation.

Availability

LP38691QSD-1.8/NOPB is available at Aetrix Electronics and suitable for portable instrumentation, battery-powered microcontrollers, and hard disk drive servo control requiring stable component supply, long-term lifecycle support, and automotive-grade reliability validation.

Supply support for LP38691QSD-1.8/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 company designing analog ICs, embedded processors, and system-on-chip solutions for industrial, automotive, and personal electronics markets.

The LP38691QSD-1.8/NOPB belongs to TI's LP3869x family of CMOS LDOs engineered for portable, battery-powered digital systems requiring fast start-up, tight output tolerance, and ceramic-capacitor compatibility-especially where low ground current and thermal robustness are critical.

FAQ

What is the minimum input voltage required for LP38691QSD-1.8/NOPB to regulate 1.8 V output?

The LP38691QSD-1.8/NOPB requires VIN ≥ (VOUT + VDO). At 500 mA, typical dropout is 250 mV for 5 V output-but for 1.8 V output, datasheet curves (Figure 22) show ~100 mV dropout at 500 mA and 25°C. Thus, minimum VIN is approximately 1.9 V. However, per recommended operating conditions, VIN must also be ≥2.7 V for full internal circuit functionality-so 2.7 V is the practical minimum input voltage for guaranteed regulation.

Does LP38691QSD-1.8/NOPB have an enable pin?

No, LP38691QSD-1.8/NOPB does not include an enable (EN) pin. It is always active when input voltage is applied and within specification (VIN ≥2.7 V). This distinguishes it from the LP38693 variant, which adds EN functionality. For applications requiring controlled power sequencing, external MOSFET switching on the IN rail is necessary when using LP38691QSD-1.8/NOPB.

Can the SNS pin of LP38691QSD-1.8/NOPB be left unconnected?

No, the SNS pin of LP38691QSD-1.8/NOPB must be connected directly to the OUT pin if remote sensing is not used. Per the datasheet, "SNS pin must be tied to OUT" for WSON-package devices. Leaving it floating violates the specified operating condition and may cause regulation instability or output inaccuracy. When remote sensing is implemented, SNS connects to the load side of the output trace-not to OUT.

What is the thermal performance of LP38691QSD-1.8/NOPB in its WSON-6 package?

LP38691QSD-1.8/NOPB in WSON-6 has R_θJA = 50.6°C/W (high-K board), R_θJB = 24.9°C/W, and R_θJC(bot) = 5.4°C/W. With the exposed thermal pad (DAP) properly soldered to ≥1 cm² of 2-oz copper, junction-to-board resistance drops significantly-enabling full 500-mA operation up to 85°C ambient. Thermal shutdown activates at 160°C junction temperature with 10°C hysteresis, providing reliable overload protection.

Is LP38691QSD-1.8/NOPB suitable for automotive applications?

LP38691QSD-1.8/NOPB is not AEC-Q100 qualified. For automotive use, TI offers the pin-compatible LP38691-Q1 variant (same WSON-6 package, 1.8 V output), which is qualified to AEC-Q100 Grade 1 (–40°C to 125°C) and specified for automotive environments. LP38691QSD-1.8/NOPB is intended for industrial and consumer applications meeting the same temperature range but without automotive qualification testing.