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Home > Products > Integrated Circuits (ICs) > Power Management (PMIC) > Voltage Regulators - DC DC Switching Regulators

STMicroelectronics L4973D3.3

Name: L4973D3.3
Brand: STMicroelectronics
SKU: L4973D3.3
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: L4973D3.3

Manufacturer:: STMicroelectronics

Category:: Voltage Regulators - DC DC Switching Regulators

Package:: 20-SOIC (0.295", 7.50mm Width)

Datasheet:: L4973D3.3.pdf

Description:: IC REG BUCK ADJ/0.5V 3.5A 20SO

Quantity:: RFQ Add To RFQ list

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Inventory:1,161

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Product details

Overview

L4973D3.3 from STMicroelectronics is a monolithic step-down switching regulator delivering 3.5 A at a fixed 3.3 V ±1% output, operating from 8 V to 55 V input, featuring internal D-MOS with 0.15 Ω typical R_DS(on), adjustable frequency up to 300 kHz, and soft-start functionality - used in industrial power supplies requiring high-efficiency DC-DC conversion.

For engineers reviewing the L4973D3.3 datasheet, L4973D3.3 pinout, L4973D3.3 application, or L4973D3.3 equivalent, key selection criteria include input voltage range (8–55 V), output current capability (3.5 A), thermal shutdown behavior, feedback disconnection protection, and SO-20 package compatibility with board-level thermal management.

Technical Context

The L4973D3.3 integrates a BCD-technology power D-MOS transistor and error amplifier with voltage feed-forward regulation, enabling stable output under wide input variation. Its oscillator supports external R/C programming for 90–300 kHz operation, and synchronization capability allows master/slave multi-regulator coordination.

Internal protections include pulse-by-pulse current limiting, hiccup-mode short-circuit response, overvoltage lockout on output, and thermal shutdown at 150 °C junction temperature. The device operates down to zero load (1 mA min.) and supports inhibit-driven sleep mode with 100 µA standby current at 24 V V_CC.

Key Specifications

Parameter	Value and Actual Design Meaning
Output voltage	Fixed 3.3 V ±1% - ensures stable logic rail generation without external resistor divider.
Max output current	3.5 A continuous - supports high-current microcontroller or FPGA core rails.
Input voltage range	8 V to 55 V - accommodates 12 V/24 V/48 V industrial bus systems with transient margin.
R_DS(on)	0.15 Ω typical - minimizes conduction loss and enables >85% efficiency at 3.3 V/3.5 A.
Switching frequency	Adjustable 90–300 kHz - balances EMI control, inductor size, and efficiency trade-offs.
Reference voltage	5.1 V ±1.5% externally available - enables precision auxiliary bias or sensing circuits.
Soft-start time	Programmable via capacitor - prevents inrush current during power-up in sensitive systems.
Thermal shutdown	Activates at 150 °C junction - protects against sustained overload or poor heatsinking.

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), optimized for industrial PCB thermal relief and automated assembly.

Pin/Terminal	Circuit Role	Design Meaning
1, 2, 3	OUT	Main power output node - connects to LC filter and load; pins 2 & 3 are paralleled for current sharing.
4–7, 14–17	GND	Signal and power ground - 12 dedicated GND pins minimize ground bounce and improve noise immunity.
8, 9	V_CC	Unregulated input supply - powers internal circuitry; requires local 100 nF decoupling.
10	INH	Inhibit control - active-high logic disables switching and reduces quiescent current to 100 µA.
11	COMP	Error amplifier output - connects to RC compensation network for loop stability tuning.
12	OSC	Oscillator timing node - sets switching frequency via external R/C (e.g., 20 kΩ + 2.7 nF = 100 kHz).
13	V_FB	Feedback input - tied directly to output for 3.3 V regulation; open for fixed-output configuration.
18	V_5.1	Precision 5.1 V reference - usable as external bias source with ±1.5% accuracy over temperature.
19	SYNC	Synchronization I/O - accepts external clock or drives slave regulators to reduce beat-frequency EMI.
20	BOOT	Bootstrap gate drive - connects to output via 100 nF capacitor to enable high-side D-MOS gate drive.

Key Features

Feature	Design Value
Voltage feed-forward regulation	Compensates for input ripple in real time - maintains tight output regulation during line transients.
Pulse-by-pulse current limiting	Clamps peak switch current cycle-by-cycle - prevents MOSFET failure during short-circuit events.
Hiccup-mode short-circuit protection	Enters low-duty-cycle restart after fault - limits average power dissipation during sustained overload.
Zero-load operation	Stable regulation down to 1 mA output - supports always-on subsystems without auxiliary bias.
Feedback disconnection protection	Shuts down if V_FB floats - avoids dangerous overvoltage conditions due to broken feedback trace.
Soft-start function	Gradually ramps output voltage - eliminates inrush current into large output capacitors or downstream loads.

Applications

Industrial PLC Power Supply

Automotive Body Control Module

Use Scenario: Converts 24 V vehicle battery or 48 V industrial bus to clean 3.3 V for microcontroller and CAN transceiver rails.

IC Role / Device Role / Timing Role: Primary buck regulator providing regulated core voltage with hiccup-mode fault recovery and thermal shutdown.

Use Value: Enables single-stage conversion from wide-input bus without pre-regulation, reducing bill-of-materials count and board area.

Use Scenario: Powers 3.3 V logic in body control units where ambient temperature exceeds 105 °C and input voltage dips to 8 V during cranking.

IC Role / Device Role / Timing Role: High-reliability step-down converter with 150 °C thermal shutdown and 8–55 V input tolerance.

Use Value: Eliminates need for external current-sense resistors or discrete protection ICs due to integrated pulse-by-pulse limiting and OVP.

Telecom Remote Radio Unit

Factory Automation Sensor Hub

Use Scenario: Supplies 3.3 V to RF front-end ICs and ADCs in outdoor base station radios exposed to wide temperature swings and EMI.

IC Role / Device Role / Timing Role: Synchronized buck regulator operating at 200 kHz to avoid interference with LTE/5G bands.

Use Value: SYNC pin enables phase alignment across multiple L4973D3.3 units, minimizing conducted EMI peaks in dense power layouts.

Use Scenario: Powers isolated sensor interface circuits in programmable logic controllers with strict EMC requirements.

IC Role / Device Role / Timing Role: Fixed-output DC-DC converter with voltage feed-forward and low-noise reference (V_5.1) for analog signal conditioning.

Use Value: External 5.1 V reference provides stable bias for precision op-amps and ADC references, improving measurement accuracy.

Equivalent & Alternatives

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

Alternative Part	Technical Difference	Application Difference	Selection Advice
LM2596S-3.3	3 A max output, 4.5–40 V input, no sync or hiccup mode, lower R_DS(on) (0.16 Ω typ.) but no V_5.1 reference.	Lacks thermal shutdown reset hysteresis and feedback disconnect protection - requires external supervision.	Choose when cost sensitivity outweighs protection robustness and 3.5 A headroom is unnecessary.
MP2315GJ-Z	3.5 A, 4.5–36 V input, 1.2 MHz fixed frequency, integrated MOSFETs, no external V_REF or sync I/O.	Higher switching frequency reduces inductor size but increases EMI filtering complexity and reduces efficiency at 48 V input.	Prefer for space-constrained designs with ≤36 V input and no requirement for multi-regulator synchronization.

Compared with LM2596S-3.3 and MP2315GJ-Z, the L4973D3.3 uniquely combines 55 V input tolerance, hiccup-mode fault recovery, and an accessible 5.1 V reference - making it optimal for industrial and automotive systems demanding wide VIN, safety-critical protection, and auxiliary analog bias.

Availability

L4973D3.3 is available at Aetrix Electronics and suitable for industrial PLCs, automotive body control modules, telecom remote radio units, and factory automation sensor hubs requiring stable component supply across extended temperature and voltage ranges.

Supply support for L4973D3.3 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, Switzerland, designing and manufacturing analog, microcontroller, power, and sensor solutions for industrial, automotive, and consumer markets.

The L4973 series belongs to ST's high-voltage monolithic DC-DC regulator product line, engineered specifically for rugged industrial and transportation applications needing wide-input, high-current, and fault-tolerant power conversion.

FAQ

What is the minimum input voltage required for stable 3.3 V output at full 3.5 A load?

The L4973D3.3 requires a minimum input voltage of 8 V to maintain regulation at 3.5 A output. Below this threshold, dropout occurs due to internal D-MOS R_DS(on) and diode forward drop - measured as ~0.6 V dropout at 3.5 A and 25 °C, increasing with temperature.

Can the L4973D3.3 be synchronized to an external clock, and what are the voltage thresholds?

Yes, the SYNC pin supports both master and slave operation. As input, it triggers switching on rising edge with high threshold ≥3.5 V and low threshold ≤0.9 V (V_CC = 8–55 V). As output, it delivers 4–4.5 V pulses at 3 mA sink, enabling precise phase alignment across multiple regulators.

How does the hiccup-mode protection behave during sustained output short-circuit?

Under sustained short-circuit, the L4973D3.3 enters hiccup mode after initial pulse-by-pulse limiting fails: it shuts down for ~20 ms, then attempts one switching cycle before repeating if fault persists. This limits average power dissipation to <0.5 W, preventing thermal runaway without manual reset.

Is the 3.3 V output trimmed using an external resistor divider, or is it internally fixed?

The 3.3 V output is internally fixed - V_FB is internally connected to the 3.3 V reference, so no external resistor divider is needed. Connecting V_FB directly to OUT configures the device for nominal 3.3 V operation with ±1% tolerance over line, load, and temperature.

L4973D3.3 Specifications

Product attributes: Attribute value

Manufacturer:: STMicroelectronics

Series:: -

Package/Case:: 20-SOIC (0.295", 7.50mm Width)

Packaging:: Tube

Product Status:: Obsolete

Function:: Step-Down

Output Configuration:: Positive

Topology:: Buck

Output Type:: Adjustable (Fixed)

Number of Outputs:: 1

Voltage - Input (Min):: 8V

Voltage - Input (Max):: 55V

Voltage - Output (Min/Fixed):: 0.5V (3.3V)

Voltage - Output (Max):: 50V

Current - Output:: 3.5A

Frequency - Switching:: 100kHz ~ 300kHz

Synchronous Rectifier:: No

Operating Temperature:: -40°C ~ 150°C (TJ)

Grade:: -

Qualification:: -

Mounting Type:: Surface Mount

Supplier Device Package:: 20-SO

L4973D3.3 FAQ

1.How can I place an order for L4973D3.3 through Aetrix?

Please submit a Request for Quotation (RFQ) for L4973D3.3 on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.

2.Are the price and stock information for L4973D3.3 reliable?

The price and inventory of L4973D3.3 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for L4973D3.3 is usually 5 days.

3.What payment methods are accepted for L4973D3.3?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for L4973D3.3 transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for L4973D3.3?

L4973D3.3 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your L4973D3.3 order is processed, you will receive an email with the shipment details and tracking number.

Note: Tracking information may take up to 24 hours to appear. Express delivery typically takes 3–5 business days.

5.How can I obtain technical support or documentation for L4973D3.3?

For technical support, including L4973D3.3 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your L4973D3.3 requirements.

6.How does Aetrix verify that L4973D3.3 is sourced from the original manufacturer or authorized distributors?

All L4973D3.3 products on Aetrix are procured from qualified distributors and authorized channels. Our dedicated quality assurance team conducts strict verification, including traceability checks and, if necessary, third-party testing. This ensures that L4973D3.3 meets industry standards.

7.What is the process for return or replacement of L4973D3.3?

All L4973D3.3 units undergo pre-shipment inspection (PSI). If there is an issue with L4973D3.3, returns or replacements are accepted under the following conditions:

1.Quantity discrepancies, incorrect items, or visible external defects (such as breakage or corrosion), acknowledged by Aetrix.

2.The issue is reported within 90 days of delivery.

3.The L4973D3.3 part is unused and in its original packaging.

Return procedure for L4973D3.3:

1.Submit a request within 90 days.

2.Obtain a Return Material Authorization (RMA) from Aetrix.

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