STMicroelectronics LD2979Z33

Overview

LD2979Z33 from STMicroelectronics is a very low dropout (LDO) linear voltage regulator in SOT23-5L package, delivering fixed 3.3 V output at up to 50 mA. It features 0.2 V typical dropout at 50 mA, 500 µA typical quiescent current in active mode, and logic-controlled inhibit for power management in battery-powered systems.

For engineers reviewing the LD2979Z33 datasheet, LD2979Z33 pinout, LD2979Z33 application, or LD2979Z33 equivalent, key selection criteria include dropout voltage under load, shutdown leakage (<1 µA), supply voltage rejection (63 dB), output noise (160 µV RMS), and thermal/overcurrent protection integrity across –25 °C to 125 °C.

Technical Context

The LD2979Z33 uses a PNP pass transistor architecture enabling ultra-low dropout voltage-just 200–400 mV at 50 mA-and maintains regulation down to VI = VO + 0.2 V. Its inhibit input (TTL-compatible, VIH ≥ 2 V, VIL ≤ 0.18 V) directly controls internal biasing without external pull-ups, and the device disables fully with <1 µA standby current when inhibited.

Stability requires only 1 µF ceramic output capacitance (ESR < 1 Ω), and internal current/thermal limiting ensures safe operation under overload or junction temperature rise. Supply voltage rejection remains ≥63 dB at 120 Hz with 10 µF output capacitor, supporting noise-sensitive analog rails.

Key Specifications

Pinout & Package

SOT23-5L surface-mount package (3.0 × 1.75 × 1.3 mm), RoHS-compliant and ECOPACK® certified, with exposed pad not connected internally.

Key Features

Applications

Equivalent & Alternatives

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

Compared with AP2112K-3.3TRG1 and MCP1700T-3302E/TT, LD2979Z33 uniquely combines sub-0.2 V dropout, integrated inhibit, and <1 µA off-state leakage-making it optimal for battery-constrained systems requiring dynamic power gating and tight input headroom.

Availability

LD2979Z33 is available at Aetrix Electronics and suitable for portable medical sensors, industrial IoT edge nodes, automotive body control modules, and smart metering subsystems requiring stable component supply across extended temperature and long-lifecycle programs.

Supply support for LD2979Z33 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, sensors, and analog devices for industrial, automotive, and consumer markets.

The LD2979 series belongs to ST's high-efficiency linear regulator product line, engineered specifically for ultra-low-power, low-noise, and space-constrained applications where precise voltage regulation and intelligent power control are critical.

FAQ

What is the minimum input voltage required for LD2979Z33 to maintain 3.3 V regulation at 50 mA?

The LD2979Z33 requires a minimum input voltage of 3.5 V to sustain regulation at 50 mA load, based on its maximum dropout voltage of 400 mV (typ. 200 mV). Below this threshold, output voltage drops linearly with input, and internal current limiting may activate if VI falls below ~3.0 V.

Can the NC pin (Pin 4) be connected to ground or left floating?

Pin 4 is internally unconnected and must remain floating-neither grounded nor tied to any voltage rail. Connecting it risks parasitic coupling or unintended current paths. The datasheet explicitly states "Not to be connected," and ST validation confirms no electrical or thermal benefit from grounding this terminal.

Does LD2979Z33 require an input capacitor, and if so, what value and type?

An input capacitor is recommended but not strictly required for stability. A 1 µF X5R/X7R ceramic capacitor placed within 2 mm of Pin 1 (VI) and Pin 2 (GND) improves transient response and reduces high-frequency noise coupling from upstream supplies. Bulk capacitance (e.g., 10 µF) is optional and depends on source impedance.

How does the inhibit function behave during power-up, and is an external pull-up needed?

The inhibit pin has no internal pull-up; it must be actively driven to ≥2 V to enable regulation. If left floating, the device remains disabled due to undefined logic state. During power-up, the host MCU should assert VIH after its own supply stabilizes-no external pull-up resistor is needed or recommended, as it would increase standby current.