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Home > Products > Integrated Circuits (ICs) > Power Management (PMIC) > DC DC Switching Controllers

STMicroelectronics L5991AD

Name: L5991AD
Brand: STMicroelectronics
SKU: L5991AD
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: L5991AD

Manufacturer:: STMicroelectronics

Category:: DC DC Switching Controllers

Package:: 16-SOIC (0.154", 3.90mm Width)

Datasheet:: L5991AD.pdf

Description:: IC REG CTRLR FLYBACK 16SO

Quantity:: RFQ Add To RFQ list

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Product details

Overview

L5991AD from STMicroelectronics is a primary-side current-mode PWM controller IC for offline and DC-DC flyback power supplies, featuring 1 MHz switching frequency, <120 µA start-up current, 1 A peak output drive, programmable soft-start, and integrated standby mode that reduces oscillator frequency under light load. It implements precise duty cycle control (0–100%), 100 ns leading-edge blanking, and latch-type overcurrent protection with hiccup-mode restart.

For engineers reviewing the L5991AD datasheet, L5991AD pinout, L5991AD application, or L5991AD equivalent, key selection criteria include its dual-frequency standby operation, synchronous capability (master/slave), VREF accuracy (5.0 V ±1.5%), UVLO hysteresis (0.5–0.8 V), and SO16 package compatibility with board-level thermal management in compact AC/DC adapters and industrial SMPS designs.

Technical Context

This controller uses fixed-frequency current-mode architecture with an internal error amplifier (60–90 dB open-loop gain, 1.7–4 MHz bandwidth) and a precision 5.0 V reference (±1.5% over temperature). Its oscillator supports independent programming of normal (f_osc) and standby (f_SB) frequencies via external R_A, R_B, and C_T, with f_osc/f_SB ratio limited to ≤5.5 to prevent oscillation.

The IC integrates fully latched PWM logic with double-pulse suppression, programmable maximum duty cycle (via pin 3 voltage and pin 15 configuration), and real-time fault handling: overcurrent detection at 1.2 V on ISEN triggers soft-start intervention and hiccup-mode recovery. Standby activation monitors VCOMP voltage thresholds (VT1 = 2.5 V falling, VT2 = 4.0 V rising) to modulate switching frequency without external circuitry.

Key Specifications

Parameter	Value and Actual Design Meaning
VREF Output	5.0 V ±1.5% at 25°C; stable reference for feedback and timing circuits
Switching Frequency	Up to 1 MHz; externally programmable for both normal and standby modes
Start-up Current	<120 µA; minimizes losses in high-resistance start-up networks
Output Drive	1 A peak source/sink; directly drives power MOSFET gates without buffer stage
Leading Edge Blanking	100 ns internal; eliminates false overcurrent trips during switch turn-on
UVLO Hysteresis	0.5–0.8 V; ensures clean power-on/power-off sequencing across input voltage transients
Standby Thresholds	VT1 = 2.5 V (falling), VT2 = 4.0 V (rising); enables automatic light-load frequency reduction

Pinout & Package

Package: SO16 (Small Outline, 16-pin, surface-mount).

Pin/Terminal	Circuit Role	Design Meaning
1 SYNC	In/Out synchronization interface	Master mode: delivers 4 V, 7 mA sync pulses; slave mode: edge-triggered input with 1 V low / 3.5 V high thresholds
2 RCT	Oscillator timing node	Connects external R_A, R_B, C_T to set f_osc and f_SB; CT charges through RA//RB (normal) or RA only (standby)
3 DC	Duty cycle control input	0–3 V input sets max duty cycle (0–100%); <1 V disables output; floating = no limit
4 VREF	5.0 V reference output	±1.5% accuracy; supplies external circuitry; requires 0.1 µF bypass to SGND
10 OUT	High-current gate driver output	1 A peak drive; 1.0 V low / 10.5 V high at 20 mA; clamped to 13 V for MOSFET protection
13 ISEN	Current sense input	1.2 V fault threshold; 100 ns blanking window; 3–15 µA input bias
14 DIS	Disable input	2.4–2.6 V threshold; latched shutdown; must not float - tie to SGND if unused
16 ST-BY	Standby mode control	Resistor-to-RCT sets standby entry point; connects to VREF or floats when disabled

Key Features

Feature	Design Value
Programmable dual-frequency operation	Independent f_osc and f_SB set via single RCT network - reduces light-load switching losses by >60% without sacrificing heavy-load regulation
Fully latched PWM with hiccup recovery	Overcurrent fault triggers soft-start reset instead of hard latch-off - maintains system controllability during sustained short-circuit conditions
Integrated 100 ns leading-edge blanking	Hardware-based blanking eliminates need for external RC filters or delay circuits on current-sense path
1 A totem-pole output stage	Drives 10 nC MOSFET gates directly at 1 MHz - avoids gate driver ICs and associated layout complexity
VREF-regulated oscillator timing	Uses stable 5.0 V reference as CT charging source - improves frequency stability vs. supply voltage variation

Applications

AC/DC Adapters

Industrial SMPS

Use Scenario: 12–24 W universal-input wall adapters for IoT sensors and smart home devices.

IC Role / Device Role / Timing Role: Primary-side controller managing flyback regulation, standby frequency scaling, and overvoltage protection via DIS pin.

Use Value: Achieves <300 mW no-load consumption using standby mode and <120 µA start-up current - meets DOE Level VI and EU CoC Tier 2 efficiency requirements.

Use Scenario: 48 V input, 12 V/2 A isolated power supply for PLC I/O modules.

IC Role / Device Role / Timing Role: Fixed-frequency current-mode controller with synchronized multi-unit operation (via SYNC pin) and hiccup-mode fault recovery.

Use Value: Enables parallel operation of three identical PSUs with automatic master election - eliminates external clock distribution circuitry.

LED Driver Power Stages

Medical Equipment Power Supplies

Use Scenario: Constant-voltage LED drivers for architectural lighting with dimming interface.

IC Role / Device Role / Timing Role: Primary controller implementing analog dimming via DC pin voltage modulation and soft-start-controlled inrush limiting.

Use Value: 0–100% programmable duty cycle allows precise LED current adjustment without secondary-side feedback components.

Use Scenario: 5 W auxiliary supply in Class II medical devices requiring reinforced isolation and low EMI.

IC Role / Device Role / Timing Role: Flyback controller with 100 ns blanking and precise VREF for stable feedback loop under ESD/EMI stress.

Use Value: 5.0 V ±1.5% reference and 1.7–4 MHz error amplifier bandwidth enable tight regulation (<±2%) across 0–100% load range.

Equivalent & Alternatives

The following parts are listed as comparable options for similar primary-side PWM controller applications.

Alternative Part	Technical Difference	Application Difference	Selection Advice
UC3844BD1R2G	Fixed 250 kHz frequency; no standby mode; 1 A output; no sync capability; 16 V UVLO	Lacks light-load frequency scaling and synchronization - unsuitable for ultra-low-no-load or multi-controller systems	Select when cost sensitivity outweighs efficiency requirements and system complexity is minimal
ICE2A265	Integrated 650 V MOSFET; 65 kHz fixed frequency; no programmable duty cycle; no hiccup mode	Monolithic solution with built-in switch - eliminates external MOSFET but forfeits design flexibility and high-frequency operation	Select for space-constrained, low-power (<15 W), non-synchronous designs where BOM count reduction is critical

Compared with UC3844BD1R2G and ICE2A265, the L5991AD uniquely combines 1 MHz operation, dual-frequency standby, and master/slave synchronization - enabling high-density, multi-rail, and ultra-efficient flyback topologies unattainable with legacy or monolithic alternatives.

Availability

L5991AD is available at Aetrix Electronics and suitable for AC/DC adapters, industrial SMPS, LED driver power stages, and medical equipment power supplies requiring stable component supply, long-term lifecycle support, and SO16-compatible thermal performance.

Supply support for L5991AD 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 specializing in power management, analog, and microcontroller solutions for industrial, automotive, and consumer markets.

The L5991AD belongs to ST's MultiPower BCD technology family - engineered for high-voltage, high-current, mixed-signal power conversion ICs targeting offline flyback and forward converters with stringent efficiency and reliability demands.

FAQ

What is the purpose of the ST-BY pin, and how is it configured?

The ST-BY pin enables automatic standby mode by reducing oscillator frequency under light load. It is configured with a resistor between ST-BY and RCT; connecting ST-BY to VREF or leaving it floating disables standby. The internal thresholds (VT1 = 2.5 V, VT2 = 4.0 V) monitor VCOMP to trigger frequency scaling without external circuitry.

How does the L5991AD implement hiccup-mode overcurrent protection?

Hiccup mode activates when ISEN voltage exceeds 1.2 V, indicating severe overload or short circuit. The IC disables PWM, discharges SS capacitor, then re-initiates soft-start. Recovery cycles repeat at a frequency determined by ISSC and ISSD currents and CSS value - maintaining thermal safety without permanent latch-off.

Can the L5991AD synchronize multiple controllers, and what are the timing constraints?

Yes - via the SYNC pin operating in master (outputting 4 V, 7 mA pulses) or slave (edge-triggered, 1 V/3.5 V thresholds) mode. When multiple units operate in parallel, the fastest automatically becomes master. For reliable synchronization, f_osc must be set 10–20% below the master frequency, and f_osc/f_SB ≤5.5 to prevent unstable transitions.

What is the role of the 100 ns leading-edge blanking, and how does it affect current sensing?

The 100 ns internal blanking window suppresses false overcurrent detection caused by MOSFET turn-on spikes and transformer leakage inductance ringing. It disables the current-sense comparator immediately after PWM turn-on, ensuring only steady-state primary current is evaluated - eliminating need for external RC filtering on the ISEN path.

L5991AD Specifications

Product attributes: Attribute value

Manufacturer:: STMicroelectronics

Series:: -

Package/Case:: 16-SOIC (0.154", 3.90mm Width)

Packaging:: Tube

Product Status:: Active

Output Type:: Transistor Driver

Function:: Step-Up/Step-Down

Output Configuration:: Positive, Isolation Capable

Topology:: Flyback

Number of Outputs:: 1

Output Phases:: 1

Voltage - Supply (Vcc/Vdd):: 7.6V ~ 20V

Frequency - Switching:: Up to 1MHz

Duty Cycle (Max):: 93%

Synchronous Rectifier:: Yes

Clock Sync:: No

Serial Interfaces:: -

Control Features:: Current Limit, Frequency Control, Soft Start

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

Grade:: -

Qualification:: -

Mounting Type:: Surface Mount

Supplier Device Package:: 16-SO

L5991AD FAQ

1.How can I place an order for L5991AD through Aetrix?

Please submit a Request for Quotation (RFQ) for L5991AD 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 L5991AD reliable?

The price and inventory of L5991AD are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for L5991AD is usually 5 days.

3.What payment methods are accepted for L5991AD?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for L5991AD transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for L5991AD?

L5991AD orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your L5991AD 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 L5991AD?

For technical support, including L5991AD datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your L5991AD requirements.

6.How does Aetrix verify that L5991AD is sourced from the original manufacturer or authorized distributors?

All L5991AD 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 L5991AD meets industry standards.

7.What is the process for return or replacement of L5991AD?

All L5991AD units undergo pre-shipment inspection (PSI). If there is an issue with L5991AD, 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 L5991AD part is unused and in its original packaging.

Return procedure for L5991AD:

1.Submit a request within 90 days.

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

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