STMicroelectronics LD2981ABM38TR

Overview

LD2981ABM38TR from STMicroelectronics is a 100mA ultra-low-dropout linear voltage regulator with fixed 3.8V output, logic-controlled inhibit function, 0.17V dropout at 100mA, 80µA typical quiescent current in active mode, and 160µVRMS output noise. It operates across –40°C to +125°C and targets low-power portable electronics requiring stable local regulation with fast transient response.

For engineers reviewing the LD2981ABM38TR datasheet, LD2981ABM38TR pinout, LD2981ABM38TR application, or LD2981ABM38TR equivalent, key selection criteria include dropout voltage at light/heavy load, inhibit input logic thresholds (0.18V low, 1.6V high), thermal shutdown at 170°C, SOT23-5L package footprint, and compatibility with low-ESR ceramic capacitors ≥2.2µF.

Technical Context

The LD2981ABM38TR integrates a PNP pass transistor enabling ultra-low dropout (7mV typ. at 1mA; 180mV typ. at 100mA) and supports TTL-compatible inhibit control on Pin 3. Its internal feedback network delivers ±0.75% initial output voltage tolerance and maintains stability with 2.2µF X7R ceramic output capacitors.

It features internal current limiting, thermal shutdown at 170°C, reverse-current protection (no body diode), and supply voltage rejection of 63dB at 1kHz. Quiescent current drops below 1µA in inhibit-off state, making it suitable for battery-backed subsystems requiring microamp-level standby power.

Key Specifications

Pinout & Package

SOT23-5L package: 2.9mm × 1.6mm × 1.3mm body, 5-pin surface-mount, lead-free ECOPACK® compliant.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MCP1700T-3802E/TT and NCP1117DT38RKG, the LD2981ABM38TR uniquely balances 100mA capability, sub-200mV dropout, integrated TTL inhibit, and 1µA shutdown - making it optimal for compact, battery-critical systems needing precise enable control without external components.

Availability

LD2981ABM38TR is available at Aetrix Electronics and suitable for portable medical sensors, industrial IoT edge nodes, automotive cabin infotainment, and smart home voice assistants requiring stable component supply with guaranteed long-term manufacturability.

Supply support for LD2981ABM38TR 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, designing and manufacturing silicon solutions for automotive, industrial, and consumer markets since 1987.

The LD2981 series belongs to ST's ultra-low-IQ LDO portfolio, engineered specifically for energy-constrained portable electronics where microamp-level shutdown current and ceramic-capacitor compatibility are mandatory design requirements.

FAQ

What is the minimum output capacitance required for stability with LD2981ABM38TR?

The LD2981ABM38TR requires a minimum 2.2µF X7R ceramic capacitor on the output for stable operation across –40°C to +125°C. This value is specified in ST's Application Notes Section 6.3 for 3.8V output versions. Using a lower-value capacitor risks oscillation unless a series resistor is added to emulate required ESR - but ST recommends adhering strictly to the 2.2µF guideline for robust performance.

Can LD2981ABM38TR be used with an input voltage below 2.5V?

No - the absolute maximum ratings table specifies 2.5V as the minimum operating input voltage (V_OP). Attempting to operate below this threshold may result in undefined regulation behavior or failure to start up. For sub-2.5V applications, ST recommends evaluating the LD2980 series or alternative ultra-low-V_IN regulators explicitly rated for such conditions.

Is the INHIBIT pin internally pulled up or pulled down?

The INHIBIT pin is not internally pulled up or down - it must never be left floating. ST's datasheet explicitly states "Inhibit is not internally pulled-up; it cannot be left floating." To ensure reliable ON operation, tie Pin 3 directly to VIN. For controlled shutdown, drive it actively to GND or ≤0.18V using a logic gate or open-drain output.

Does LD2981ABM38TR support reverse current protection?

Yes - the LD2981ABM38TR uses a PNP pass transistor without an inherent body diode, preventing reverse current flow from VOUT to VIN when output voltage exceeds input. Under reverse-bias conditions (e.g., V_REV applied to VOUT), only ~160µA flows through internal feedback resistors to GND, as confirmed in Section 6.6 and Figure 21 of the datasheet. This eliminates need for external blocking diodes in back-powering scenarios.