STMicroelectronics LD2979M38TR

Overview

LD2979M38TR from STMicroelectronics is a very low dropout linear voltage regulator delivering a fixed 3.8 V output with 50 mA maximum load current, 0.2 V typical dropout at 50 mA, and 500 µA typical quiescent current in active mode. It features TTL-compatible logic-controlled shutdown (INHIBIT pin), internal thermal/current limiting, and operates across –25 °C to 125 °C for use in battery-powered sensor nodes and portable instrumentation.

For engineers reviewing the LD2979M38TR datasheet, LD2979M38TR pinout, LD2979M38TR application, or LD2979M38TR equivalent, key selection criteria include dropout voltage at 50 mA, shutdown threshold (V_IH = 2 V), output noise (160 µV RMS), supply voltage rejection (63 dB), and SOT23-5L footprint compatibility in space-constrained designs.

Technical Context

The LD2979M38TR implements a PNP-based LDO architecture enabling ultra-low dropout (200–400 mV at 50 mA) and stable regulation with only 1 µF ceramic output capacitance. Its inhibit input accepts TTL-level logic (V_IL ≤ 0.18 V, V_IH ≥ 2 V) and draws negligible current (<1 µA at 0 V, <15 µA at 5 V), supporting precise power gating.

It maintains output accuracy of ±2% over temperature (–25 °C to 125 °C) and line regulation of 0.028%/V, with 63 dB PSRR at 120 Hz and 160 µV RMS output noise (300 Hz–50 kHz bandwidth). Internal protection includes thermal foldback and current limiting up to 100 mA.

Key Specifications

Pinout & Package

LD2979M38TR is housed in a RoHS-compliant, lead-free SOT23-5L package (3.0 × 1.75 × 1.3 mm), optimized for automated placement and thermal performance in high-density PCB layouts.

Key Features

Applications

Equivalent & Alternatives

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

Compared with AP2210K-3.8TRG1 and TPS78038DRVR, LD2979M38TR uniquely balances sub-0.25 V dropout, TTL-compatible inhibit, and 1 µF stability-making it optimal for compact, battery-fed systems needing both efficiency and controllability without sacrificing noise performance.

Availability

LD2979M38TR is available at Aetrix Electronics and suitable for portable medical sensors, industrial wireless transceivers, and automotive cabin sensors requiring stable component supply with long lifecycle visibility and consistent parametric performance.

Supply support for LD2979M38TR 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

STMicroelectronics is a global semiconductor leader headquartered in Geneva, Switzerland, designing and manufacturing microcontrollers, power management ICs, analog chips, and MEMS sensors for industrial, automotive, and consumer markets.

The LD2979 series belongs to ST's ultra-low-dropout linear regulator product line, engineered specifically for energy-constrained, noise-sensitive applications where minimal input-to-output voltage differential and precise logic-controlled power gating are critical.

FAQ

What is the minimum input voltage required for regulation at full 50 mA load?

The LD2979M38TR requires input voltage ≥ VO + V_DROP. With 3.8 V nominal output and max 600 mV dropout at 50 mA and 125 °C, minimum VI is 4.4 V. At room temperature, 4.0 V suffices due to typical 200–400 mV dropout. Input below this causes output collapse or unregulated behavior.

Can the INHIBIT pin be left unconnected?

No. The INHIBIT pin has no internal pull-up or pull-down. Leaving it floating risks undefined state and unintended shutdown or oscillation. Per ST's datasheet, it must be actively driven to ≥2 V for ON or ≤0.18 V for OFF-never left open. A 100 kΩ pull-up to VI is acceptable if always-on operation is intended.

Is an output capacitor mandatory, and what type is recommended?

Yes-a minimum 1 µF ceramic capacitor is mandatory between VO and GND for stability. ST specifies X5R or X7R dielectrics with ≤100 mΩ ESR. Tantalum or aluminum electrolytic caps are not recommended due to higher ESR and potential instability. Larger values (e.g., 2.2 µF) improve transient response but are not required.

Does LD2979M38TR support reverse polarity or reverse current protection?

No. The device lacks built-in reverse-voltage or reverse-current blocking. If input can be reversed (e.g., during hot-swap or battery insertion), an external series Schottky diode or ideal diode controller is required. Reverse current flow from VO to VI may damage the IC or cause latch-up if VI falls below VO while powered.