STMicroelectronics L4957AD3.3

Overview

L4957AD3.3 from STMicroelectronics is a 3.3V fixed-output ultra-low-dropout linear regulator with internal N-channel MOSFET (200mΩ typical R_DS(on)), capable of delivering up to 5A continuous output current across 3V–14V input range, featuring 0.6V max dropout at 2A, ±2% output voltage tolerance (including line/load variation), and integrated thermal shutdown and short-circuit protection. It serves as a post-regulator for SMPS in processor I/O supplies and low-voltage memory systems.

For engineers reviewing the L4957AD3.3 datasheet, L4957AD3.3 pinout, L4957AD3.3 application, or L4957AD3.3 equivalent, key selection criteria include dropout voltage at full load, quiescent current under light load, thermal resistance (R_thJC = 3°C/W), stability with ≥22µF output capacitance, and compatibility with 3.3V bus-to-3.3V rail regulation where minimal voltage overhead is required.

Technical Context

The L4957AD3.3 employs an internal charge-pump-assisted N-channel DMOS pass transistor to achieve ultra-low dropout, enabling operation with (V_IN – V_OUT) as low as 0.6V at 2A. Its error amplifier uses on-chip trimmed voltage reference to maintain ±2% total output accuracy over temperature and load.

Thermal protection activates at ~150°C junction temperature with 29°C hysteresis, while current limiting engages at 5.1–7.5A depending on junction temperature. Ripple rejection reaches 60–75dB at 120Hz, supporting use after switching regulators without additional filtering.

Key Specifications

Pinout & Package

Supplied in D2PAK (TO-263) package: single-row 3-pin surface-mount outline with exposed thermal pad (pin 2 = GND, electrically and thermally connected to tab).

Key Features

Applications

Equivalent & Alternatives

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

Compared with TLV1117-33CDCY and NCP1117DT33T5G, the L4957AD3.3 uniquely delivers 5A continuous current with 0.6V dropout and 3°C/W junction-to-case thermal resistance - making it the only viable option for high-density, high-power motherboard and graphics card LDO applications requiring both current and thermal headroom.

Availability

L4957AD3.3 is available at Aetrix Electronics and suitable for motherboard power delivery, processor I/O regulation, and graphics card auxiliary rail applications requiring stable component supply, long-term lifecycle support, and traceable sourcing for industrial and computing OEMs.

Supply support for L4957AD3.3 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 analog, microcontroller, power, and sensor solutions for automotive, industrial, and consumer markets.

The L4957A series was developed specifically for high-current, ultra-low-dropout regulation in computing infrastructure - targeting cost-effective replacement of discrete MOSFET+controller LDO designs in motherboards, chipsets, and graphics subsystems.

FAQ

What is the minimum input voltage required for stable 3.3V output at 5A?

The L4957AD3.3 requires (V_OUT + dropout) = 3.3V + 0.6V = 3.9V minimum input to sustain 5A output. At lower input voltages, current limit reduces progressively - e.g., at 3.5V input, maximum sustainable output current drops to ~3.2A per Figure 6 in the datasheet.

Can the L4957AD3.3 operate without an input bypass capacitor?

No. The datasheet mandates ≥10µF capacitor on the IN pin to stabilize internal charge pump operation and prevent oscillation. Omitting it risks erratic regulation, increased ripple, and potential thermal shutdown due to gate drive instability.

Is the D2PAK package lead-free and RoHS-compliant?

Yes. Per ST's ECOPACK® documentation, the L4957AD3.3 uses lead-free second-level interconnects and complies with RoHS Directive 2011/65/EU. The package marking and inner box label indicate compliance per JEDEC JESD97.

How does thermal shutdown interact with continuous 5A operation?

At 5A and 3.9V input, power dissipation is ~3W (5A × 0.6V). With R_thJC = 3°C/W and proper PCB copper pour, junction temperature rise is ~9°C above case - well below 150°C shutdown threshold. Sustained 5A operation is thermally feasible with ≥25mm² 2oz copper thermal pad.