STMicroelectronics L4973D5.1

Overview

L4973D5.1 from STMicroelectronics is a monolithic step-down switching regulator delivering 3.5 A at a fixed 5.1 V ±1% output, operating from 8 V to 55 V input, featuring internal D-MOS (R_DS(on) = 0.15 Ω typ.), adjustable switching frequency up to 300 kHz, and integrated soft-start, thermal shutdown, and overvoltage protection - deployed in industrial power supplies and automotive body control modules.

For engineers reviewing the L4973D5.1 datasheet, L4973D5.1 pinout, L4973D5.1 application, or L4973D5.1 equivalent, key selection criteria include input voltage range (8–55 V), output accuracy (±1% at 5.1 V), current capability (3.5 A continuous), package thermal resistance (R_thJA = 80 °C/W), and synchronization support for multi-regulator systems.

Technical Context

The L4973D5.1 implements voltage-mode PWM control with feed-forward compensation, using an internal error amplifier (transconductance = 2.5 mS) and oscillator with external R/C programming (90–300 kHz). Its bootstrap gate drive enables high-side N-channel MOSFET operation without external high-voltage biasing.

Protection architecture includes pulse-by-pulse current limiting (4.5 A typ.), hiccup-mode short-circuit response, feedback disconnection detection, and thermal shutdown at 150 °C. The device supports zero-load operation (2.7 mA quiescent current) and deep sleep via INH pin (100 µA standby at V_CC = 24 V).

Key Specifications

Pinout & Package

Package: SO-20 (12+4+4) surface-mount package with exposed thermal pad (R_thJA = 80 °C/W, R_thJP = 15 °C/W), rated for 4 W max power dissipation at T_pins = 90 °C.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar step-down regulator applications.

Compared with LM2596S-5.0 and TPS54360B, the L4973D5.1 uniquely combines fixed 5.1 V ±1% accuracy, externally accessible reference, hiccup-mode protection, and synchronization - making it optimal for systems demanding precision, reliability, and coordinated multi-rail operation without added components.

Availability

L4973D5.1 is available at Aetrix Electronics and suitable for industrial PLC power supplies, automotive body control modules, and telecom remote radio units requiring stable component supply across extended temperature and voltage ranges.

Supply support for L4973D5.1 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 power management applications.

The L4973 series belongs to ST's high-voltage monolithic DC-DC converter product line, engineered specifically for rugged, high-current buck regulation in harsh environments where wide input range, thermal resilience, and integrated protection are mandatory.

FAQ

What is the minimum input voltage required for L4973D5.1 to regulate 5.1 V output?

The L4973D5.1 requires a minimum input voltage of 8 V to maintain regulation at 5.1 V output. Below this threshold, the internal control loop cannot sustain duty cycle or gate drive, resulting in dropout. Dropout voltage is typically 0.4 V at 3.5 A, so 5.5 V input would be insufficient - 8 V is the absolute functional limit per datasheet Section 4.

Can L4973D5.1 be used with an adjustable output voltage below 5.1 V?

No - the L4973D5.1 is factory-trimmed for fixed 5.1 V output and lacks internal circuitry to support outputs below that level. Attempting to force lower voltages via external feedback risks instability or failure to regulate; ST explicitly states in Section 2.2 that outputs less than 3.3 V require the L4973V3.3 variant and special design considerations (see Figure 30).

How does the SYNC pin function in master vs. slave configuration?

When configured as master, the SYNC pin outputs a 4–4.5 V logic pulse (0.2–0.35 µs width) synchronized to the internal oscillator. As slave, it accepts external clock signals ≥3.5 V high-level threshold and locks internal frequency/phase. No external pull-up/down is required - mode is determined by whether the pin drives or receives the signal in the application circuit.

Is thermal derating required when operating L4973D5.1 at 3.5 A continuous current?

Yes - at 3.5 A and 55 V input, power dissipation exceeds 4 W (per Figure 29), exceeding the SO-20 package's 4 W maximum at T_pins = 90 °C. Derating is mandatory: at ambient 70 °C with standard PCB layout, maximum sustainable current drops to ~2.8 A unless enhanced copper area or forced airflow is applied per Table 3 thermal data.