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

STMicroelectronics L4978

Name: L4978
Brand: STMicroelectronics
SKU: L4978
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: L4978

Manufacturer:: STMicroelectronics

Category:: Voltage Regulators - DC DC Switching Regulators

Package:: 8-DIP (0.300", 7.62mm)

Datasheet:: L4978.pdf

Description:: IC REG BUCK ADJ 2A 8DIP

Quantity:: RFQ Add To RFQ list

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Inventory:497

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Product details

Overview

L4978 from STMicroelectronics is a monolithic step-down switching regulator IC with integrated 2A D-MOS power transistor (R_DS(on) = 0.25Ω typ.), operating from 8V to 55V input and delivering adjustable output from 3.3V to 50V. It features internal 3.3V ±1% reference, voltage feedforward control, pulse-by-pulse current limiting, and thermal shutdown-used in industrial power supplies requiring high-efficiency DC-DC conversion at up to 300kHz.

For engineers reviewing the L4978 datasheet, L4978 pinout, L4978 application, or L4978 equivalent, key selection criteria include its wide input range (8–55V), soft-start programmability via external capacitor, feedback disconnection protection, zero-load operation capability, and dual-package availability (DIP-8 and SO16W) for through-hole or SMD assembly.

Technical Context

The L4978 implements voltage-mode PWM control with feedforward compensation, where oscillator frequency is set by external R_OSC and C_OSC, and duty cycle is modulated by error amplifier output driving an internal RS latch. Its internal 3.3V reference feeds both feedback comparator and soft-start circuitry, enabling precise regulation across temperature (±0.4mV/°C drift) and line (≤10mV line regulation).

Protection architecture includes hiccup-mode short-circuit response triggered by overcurrent detection, thermal shutdown at T_j ≥ 150°C, and inhibit-driven zero-quiescent-current sleep mode (I_QST-BY = 100–300µA). The BOOT pin supports high-side gate drive via external bootstrap capacitor, enabling efficient N-channel MOSFET switching without external high-voltage level shifters.

Key Specifications

Parameter	Value and Actual Design Meaning
Input Voltage Range	8V to 55V - supports wide-range industrial and automotive battery-fed systems without pre-regulation.
Output Voltage Range	3.3V to 50V adjustable - set via external resistor divider on FB pin; 3.3V fixed when FB tied directly to output.
Max Output Current	2A continuous - enabled by integrated 0.25Ω R_DS(on) D-MOS switch and thermal design margin up to 150°C junction.
Switching Frequency	Adjustable up to 300kHz - set externally via R/C on OSC pin; enables optimization of size vs. efficiency trade-off.
Reference Voltage	3.3V ±1% at 25°C - high-precision internal bandgap reference ensures stable output regulation under load and line variation.
Quiescent Current	4–6mA operating / 100–300µA standby - enables low-power sleep mode during system idle without external enable circuitry.
Efficiency	87% at 3.3V/2A - achieved via low R_DS(on), optimized gate drive, and voltage feedforward reducing loop gain dependency on input.

Pinout & Package

Available in two packages: plastic DIP-8 (through-hole) and SO16W (wide-body surface-mount). Both packages share identical pin functions but differ in thermal resistance (DIP-8: 90°C/W, SO16W: 110°C/W) and pin count mapping due to NC pins.

Pin/Terminal	Circuit Role	Design Meaning
1, 7, 8, 9, 10, 15, 16	No Connect (NC)	Not internally bonded - must be left floating or grounded per layout guidelines; no electrical function.
2	GND	Power and signal ground reference for internal circuits, error amplifier, and oscillator.
3	SS_INH	Active-low inhibit/soft-start control: grounding disables device; capacitor to GND sets soft-start time.
4	OSC	Oscillator timing node: external R to V_CC and C to GND set switching frequency and enable line feedforward.
5	OUT	Power switch output node - connects to external inductor and freewheeling diode/capacitor network.
6	V_CC	Unregulated input supply - powers internal logic, gate driver, and bias circuits; must be ≥8V.
11	BOOT	Bootstrap capacitor connection - lifts gate drive voltage above OUT to fully enhance internal N-MOSFET.
12	COMP	Error amplifier output - connects to external RC compensation network for loop stability.
13	FB	Feedback input - senses output voltage via resistive divider; open-loop if disconnected (protected).
14	V_CC	Duplicate V_CC pin - electrically tied to pin 6; used for decoupling and current sharing in SO16W package.

Key Features

Feature	Design Value
Voltage Feedforward Regulation	Compensates for input ripple without increasing loop gain - improves transient response and reduces output filter requirements.
Pulse-by-Pulse Current Limiting	Real-time overcurrent detection per switching cycle - prevents MOSFET failure during overload or short-circuit events.
Hiccup-Mode Short-Circuit Protection	Auto-retry shutdown after fault clears - avoids thermal runaway while maintaining system recoverability.
Zero-Load Operation	Maintains regulation down to 0A output - eliminates need for dummy loads in battery-powered or standby applications.
Feedback Disconnection Protection	Clamps output to safe voltage if FB pin opens - prevents uncontrolled overvoltage damage to downstream circuitry.

Applications

Industrial Power Supply

Automotive Body Control Module

Use Scenario: 24V truck battery powering 5V microcontroller and CAN transceiver rails.

IC Role / Device Role / Timing Role: Primary step-down regulator converting 8–36V nominal battery to stable 5.1V output.

Use Value: Wide input range accommodates cold-crank (6V) and load-dump (60V) transients without external clamping.

Use Scenario: Central body controller supplying 12V actuator drivers and 3.3V sensor interface from 12V battery.

IC Role / Device Role / Timing Role: Dual-output capable regulator (via external divider) delivering isolated 12V and 3.3V rails.

Use Value: Internal 3.3V reference and hiccup-mode protection ensure reliable startup and fault recovery in harsh EMI environments.

Programmable Logic Controller (PLC) I/O Module

Telecom Remote Radio Unit (RRU)

Use Scenario: DIN-rail mounted PLC module converting 48V telecom supply to 3.3V FPGA core and 5V I/O voltage.

IC Role / Device Role / Timing Role: High-efficiency buck converter supporting 2A peak load with minimal heatsink requirement.

Use Value: 87% efficiency at full load reduces thermal stress in sealed enclosures; soft-start prevents inrush into bulk capacitance.

Use Scenario: Outdoor base station RRU requiring 28V bias supply for RF power amplifiers from -48V DC plant.

IC Role / Device Role / Timing Role: Step-up compatible buck topology (with external components) generating 28V from -48V input.

Use Value: Adjustable 3.3–50V output and 300kHz max frequency allow compact magnetics design for space-constrained outdoor housing.

Equivalent & Alternatives

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

Alternative Part	Technical Difference	Application Difference	Selection Advice
LM2596-ADJ	Fixed 150kHz freq, no voltage feedforward, lower max input (40V), no hiccup mode.	Lacks protection for sustained short-circuit; unsuitable for automotive load-dump conditions.	Prefer L4978 where input exceeds 40V or hiccup-mode safety is required.
TPS54202	Higher integration (integrated FETs, light-load PFM), but max input only 28V and no feedforward.	Better light-load efficiency but limited to low-voltage industrial use; no 55V tolerance.	Choose L4978 for >40V input or feedforward-dependent transient performance.

Compared with LM2596-ADJ and TPS54202, the L4978 uniquely combines 55V input rating, voltage feedforward, hiccup-mode protection, and zero-load operation-making it optimal for ruggedized 24/48V systems where reliability under fault and transient conditions is critical.

Availability

L4978 is available at Aetrix Electronics and suitable for industrial power supplies, automotive body controllers, PLC I/O modules, and telecom remote radio units requiring stable component supply across extended temperature and voltage ranges.

Supply support for L4978 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, specializing in power management, analog, microcontrollers, and automotive-grade ICs.

The L4978 belongs to ST's legacy high-voltage DC-DC regulator product line, designed specifically for robust industrial and transportation applications demanding wide-input, high-current, and fault-tolerant power conversion.

FAQ

What is the minimum input voltage required for L4978 to regulate 3.3V output?

The L4978 requires a minimum input voltage of 8V to maintain regulation at any output voltage, including 3.3V. This is due to internal bias circuitry and gate drive voltage requirements-not dropout-limited like linear regulators. Below 8V, the device ceases switching and enters undervoltage lockout.

Can L4978 operate without an external soft-start capacitor?

Yes, but not recommended. Leaving SS_INH open or unconnected results in immediate full-duty startup, causing high inrush current into output capacitors. A capacitor (typically 100nF–1µF) between SS_INH and GND is required to control ramp rate and limit peak input current during startup.

How does the L4978 handle feedback loop disconnection?

When the FB pin is disconnected or open-circuited, the internal error amplifier clamps COMP output low, forcing PWM duty cycle to minimum and limiting output voltage to ≈3.3V + V_drop. This failsafe behavior prevents destructive overvoltage and is confirmed in Electrical Characteristics Table 6 under "Protection against feedback disconnection".

Is the BOOT pin mandatory for operation, and what capacitor value is recommended?

Yes, the BOOT pin is mandatory-it supplies gate drive voltage above the OUT node to fully enhance the internal N-MOSFET. A 100nF ceramic capacitor (X7R, 16V+ rating) between BOOT and OUT is standard; values from 47nF to 220nF are acceptable depending on switching frequency and load current.

L4978 Specifications

Product attributes: Attribute value

Manufacturer:: STMicroelectronics

Series:: -

Package/Case:: 8-DIP (0.300", 7.62mm)

Packaging:: Tube

Product Status:: Active

Function:: Step-Down

Output Configuration:: Positive

Topology:: Buck

Output Type:: Adjustable

Number of Outputs:: 1

Voltage - Input (Min):: 8V

Voltage - Input (Max):: 55V

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

Voltage - Output (Max):: 50V

Current - Output:: 2A

Frequency - Switching:: 100kHz ~ 300kHz

Synchronous Rectifier:: No

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

Grade:: -

Qualification:: -

Mounting Type:: Through Hole

Supplier Device Package:: 8-DIP

L4978 FAQ

1.How can I place an order for L4978 through Aetrix?

Please submit a Request for Quotation (RFQ) for L4978 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 L4978 reliable?

The price and inventory of L4978 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for L4978 is usually 5 days.

3.What payment methods are accepted for L4978?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for L4978 transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for L4978?

L4978 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your L4978 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 L4978?

For technical support, including L4978 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your L4978 requirements.

6.How does Aetrix verify that L4978 is sourced from the original manufacturer or authorized distributors?

All L4978 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 L4978 meets industry standards.

7.What is the process for return or replacement of L4978?

All L4978 units undergo pre-shipment inspection (PSI). If there is an issue with L4978, 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 L4978 part is unused and in its original packaging.

Return procedure for L4978:

1.Submit a request within 90 days.

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

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