STMicroelectronics LD2979M33TR

Overview

LD2979M33TR from STMicroelectronics is a very low dropout linear voltage regulator delivering a fixed 3.3 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 current/thermal protection, and operates across –25 °C to 125 °C for use in battery-powered microcontroller subsystems and low-noise sensor interfaces.

For engineers reviewing the LD2979M33TR datasheet, LD2979M33TR pinout, LD2979M33TR application, or LD2979M33TR equivalent, key selection criteria include dropout voltage at 50 mA, shutdown logic threshold (2 V high / 0.18 V low), stability with 1 µF ceramic output capacitor, supply voltage rejection (63 dB at 120 Hz), and SOT23-5L thermal performance in space-constrained designs.

Technical Context

The LD2979M33TR implements a PNP-based LDO architecture enabling ultra-low dropout by minimizing base-emitter voltage overhead. Its inhibit input directly controls the pass transistor bias, allowing full shutdown with near-zero quiescent current (<1 µA) when INHIBIT < 0.18 V.

Stability is achieved with only 1 µF ceramic output capacitance due to internal compensation optimized for low-ESR capacitors. The device maintains ±2% output accuracy over temperature (–25 °C to 125 °C) and line regulation of 0.064 %/V across 3.85 V to 16 V input range.

Key Specifications

Pinout & Package

SOT23-5L package: 5-pin surface-mount, 1.3 mm height, 2.8 × 1.75 mm footprint, ECOPACK® lead-free, rated for 125 °C junction operation.

Key Features

Applications

Equivalent & Alternatives

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

Compared with AP2204K-3.3TRG1 and MCP1700T-3302E/TT, the LD2979M33TR uniquely combines 0.2 V dropout, 500 µA active I_Q, and integrated TTL-compatible inhibit - making it optimal for compact, dynamically powered embedded systems where efficiency, noise, and control integration are jointly constrained.

Availability

LD2979M33TR is available at Aetrix Electronics and suitable for wireless sensor nodes, industrial PLC I/O modules, automotive body control units, and medical wearable front-ends requiring stable component supply with guaranteed long-term availability.

Supply support for LD2979M33TR 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 silicon solutions for automotive, industrial, and consumer markets since 1987.

The LD2979 series belongs to ST's precision analog LDO portfolio, engineered specifically for ultra-low-power, low-noise local regulation in battery-operated and thermally demanding embedded systems.

FAQ

What is the minimum input voltage required for stable 3.3 V output at 50 mA load?

The LD2979M33TR requires input voltage ≥3.5 V to maintain regulation at 50 mA, based on its 200–400 mV dropout specification. At 3.7 V input, it delivers full 3.3 V output with margin; operation below 3.5 V risks dropout and output collapse. Input must also exceed 3.3 V + V_d(I_O) across temperature and process variation.

Can the INHIBIT pin be left floating during PCB layout?

No - the INHIBIT pin is not internally pulled up or down and must never be left floating. Floating states cause unpredictable enable/disable behavior and potential shoot-through current. Tie to VI via 10 kΩ resistor for default-on operation, or to GND for default-off. Always verify logic thresholds (VIH ≥2 V, VIL ≤0.18 V) with driving source.

Is a 1 µF ceramic capacitor sufficient for stability across all operating conditions?

Yes - ST specifies 1 µF X5R/X7R ceramic capacitor (with ESR < 1 Ω) as sufficient for stability per datasheet Figure 12–14. Larger values (e.g., 2.2 µF) improve transient response but are not required. Avoid high-ESR types like aluminum electrolytic; ensure capacitor placement is within 2 mm of VO and GND pins to preserve high-frequency PSRR.

Does the LD2979M33TR support reverse-voltage or reverse-current protection?

No - the device lacks built-in reverse-voltage or reverse-current protection. If input polarity reversal is possible (e.g., battery insertion error), external protection (series diode or MOSFET-based circuit) is required. Reverse current flow from VO to VI may damage the internal pass transistor and is not rated per absolute maximum ratings table.