STMicroelectronics L4963D

Overview

L4963D from STMicroelectronics is a monolithic step-down switching regulator delivering 1.5A output current with adjustable output voltage from 5.1V to 36V, operating in discontinuous variable-frequency mode. It integrates a precise 5.1V on-chip reference (±2%), internal current limiting, thermal shutdown, open-collector reset and power-fail outputs, and TTL-level remote inhibit - used in industrial power supplies requiring stable mid-power DC-DC conversion.

For engineers reviewing the L4963D datasheet, L4963D pinout, L4963D application, or L4963D equivalent, key selection considerations include its 5.1–36V adjustable output range, 1.5A load capability, SO20 package thermal performance (R_{th j-amb} = 85°C/W), oscillator frequency programmability via external R/C, and dual monitoring outputs for microprocessor supervision.

Technical Context

The L4963D implements a self-oscillating discontinuous conduction mode (DCM) buck topology without requiring external frequency compensation. Regulation relies on two comparators comparing feedback voltage against a 5.1V internal reference, with latch-controlled power stage timing determined by inductor discharge detection at –0.1V.

Its reset circuit provides programmable delay via external capacitor on pin 10, while the power-fail monitor senses input voltage via an external divider on pin 7 (threshold ~19V typical when open). The device supports remote on/off control via TTL-compatible inhibit input (pin 16) and delivers reference voltage (pin 12) and oscillator waveform (pin 17) for system integration.

Key Specifications

Pinout & Package

Package: SO20 (Small Outline, 20-pin, body size 12.6 × 7.6 mm, lead pitch 1.27 mm, max height 2.65 mm).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar switching regulator applications.

Compared with LM2596S-ADJ and MP1584EN-LF-Z, the L4963D uniquely integrates microprocessor supervision (reset + power-fail), operates up to 46V input, and eliminates compensation components - making it optimal for industrial systems needing robust, self-contained DC-DC regulation with deterministic startup/shutdown behavior.

Availability

L4963D is available at Aetrix Electronics and suitable for industrial PLC power supplies, embedded microcontroller boards, test equipment power modules, and motor drive control boards requiring stable component supply and long-term lifecycle support.

Supply support for L4963D 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, power, microcontroller, and sensor solutions for industrial, automotive, and consumer markets.

The L4963D belongs to ST's legacy power management IC portfolio targeting rugged, cost-effective DC-DC conversion in industrial automation and embedded control systems where integrated supervision and wide-input operation are essential.

FAQ

What is the minimum input voltage required for stable 5.1V output?

The L4963D requires a minimum input voltage of 9 V to maintain regulation at 5.1 V output under full 1.5 A load, as specified in the Electrical Characteristics table. Below 9 V, dropout behavior occurs - output voltage drops linearly with input, and internal regulation ceases. This ensures sufficient headroom for the internal switch and control circuitry to function reliably.

Can the L4963D generate a 3.3V output directly?

No - the L4963D's internal reference is fixed at 5.1 V, and its feedback architecture is designed for output voltages ≥5.1 V. To achieve 3.3 V, an external LDO (e.g., LD1117V33) must be used downstream, or a different regulator with lower reference voltage (e.g., LM2678-3.3) should be selected. Attempting to force sub-5.1 V operation violates the regulation loop design.

How is the reset delay time calculated for the L4963D?

The reset delay is set by a capacitor (C_DELAY) connected between pin 10 (Reset Delay Input) and ground. Typical delay ranges from ~10 ms (100 nF) to ~500 ms (10 µF), based on empirical characterization in Figure 3b and evaluation board documentation. No exact formula is provided in the datasheet; designers select C_DELAY experimentally or via reference designs like Fig. 26.

Does the L4963D support synchronous rectification?

No - the L4963D uses an internal N-channel power MOSFET driving an external catch diode (e.g., BYW98). It does not provide gate drive signals for a synchronous rectifier FET. The discontinuous conduction mode and open-drain output stage are incompatible with synchronous rectification control, and no secondary gate driver pins or timing signals are provided.