Send an Inquiry

To receive a quote for your project, please fill in the following information, and we’ll get back to you promptly.

Submit Inventory List

Please fill in the following information, and we’ll get back to you promptly.

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

STMicroelectronics E-L5991AD

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

Compare

Part No.:: E-L5991AD

Manufacturer:: STMicroelectronics

Category:: DC DC Switching Controllers

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

Datasheet:: E-L5991AD.pdf

Description:: IC REG CTRLR FLYBACK 16SOIC

Quantity:: RFQ Add To RFQ list

Payment:

Shipping:

Inventory:1,780

Please send an inquiry. Send us your inquiry, and we will respond immediately.

Product details

Overview

E-L5991AD from STMicroelectronics is a primary-side current-mode PWM controller IC for offline and DC-DC flyback power supplies, featuring programmable soft-start (ISSC = 14–26 µA), standby mode with oscillator frequency reduction, 1 A peak totem-pole output drive, and internal 100 ns leading-edge blanking on current sense. It operates up to 1 MHz, supports IN/OUT synchronization, and integrates precise 5.0 V ±1.5% reference, UVLO with hysteresis (VCCON = 7.8–8.4 V), and latched disable for overvoltage protection.

For engineers reviewing the E-L5991AD datasheet, E-L5991AD pinout, E-L5991AD application in flyback converters, or E-L5991AD equivalent for primary-side control, this device delivers verified current-mode regulation, programmable duty cycle (0–93%), dual-threshold standby activation (VT1 = 2.5 V, VT2 = 4.0 V), and fault-handling via hiccup-mode overcurrent protection with restart delay.

Technical Context

The E-L5991AD implements fixed-frequency current-mode PWM control using a BCD60II process, with oscillator timing set by external RCT network (RA, RB, CT) and dual-frequency operation-normal (fosc) and standby (fSB)-programmable via pin 16 (ST-BY) and pin 15 (DC-LIM). Its error amplifier (pin 5/6) provides 60–90 dB open-loop gain and 1.7–4 MHz unity-gain bandwidth, with compensation networks referenced to VFB and COMP.

Standby mode activates when VCOMP falls below VT1 (2.5 V), reducing switching frequency to minimize light-load losses; recovery occurs at VT2 (4.0 V) with hysteresis to prevent oscillation. Current sensing uses internal 100 ns blanking and a 1.1–1.3 V fault threshold (Vt), while pulse-by-pulse limiting transitions to hiccup mode upon sustained overcurrent detection at ISEN.

Key Specifications

Parameter	Value and Actual Design Meaning
VREF Output	5.0 V ±1.5% at 25°C; powers external circuitry and sets oscillator timing
Max Switching Frequency	1 MHz; enables compact magnetics and high-efficiency flyback designs
Start-up Current	< 120 µA; minimizes auxiliary supply losses during initial power-up
Output Drive Capability	1 A peak source/sink; directly drives Power MOSFET gates without external buffers
UVLO Thresholds	VCCON = 7.8–8.4 V, VCCOFF = 7.0–7.6 V, hysteresis = 0.5–0.8 V; ensures clean enable/disable under brownout
Soft-Start Charge Current	14–26 µA; sets controlled ramp time for VCOMP to prevent inrush current
Current Sense Fault Threshold	1.1–1.3 V at ISEN; triggers hiccup-mode protection before transformer saturation
Standby Thresholds	VT1 = 2.5 V (falling), VT2 = 4.0 V (rising); defines load-dependent oscillator frequency shift

Pinout & Package

Package: SO16 (small-outline integrated circuit, 16-pin, surface-mount).

Pin/Terminal	Circuit Role	Design Meaning
1 SYNC	In/Out synchronization interface	Master: outputs 4 V, 7 mA sync pulses; slave: edge-triggered input with 1 V low / 3.5 V high thresholds
2 RCT	Oscillator timing node	Connects external RA, RB, CT to set fosc and fSB; CT charges through RA//RB (normal) or RA only (standby)
3 DC	Duty cycle control input	Bias voltage (1–3 V) sets max duty cycle 0–93%; floating = no limit; <1 V disables output
4 VREF	Internal 5 V reference output	±1.5% accuracy; sinks 30–150 mA; requires 0.1 µF bypass to SGND for stability
5 VFB	Error amplifier inverting input	Compares feedback signal to 2.5 V internal reference; connects to compensation network with COMP
6 COMP	Error amplifier output	Drives PWM comparator; low-impedance voltage-mode output; crossover must be ≤ fSB/5 for stability
7 SS	Soft-start capacitor node	Charged by 14–26 µA current; clamps COMP during start-up and hiccup recovery
8 VCC	Signal section supply	UVLO-enabled (7.8–8.4 V turn-on); internal 25 V Zener clamp; decouple with local film capacitor
9 VC	Power stage supply	Supplies gate driver; connect bulk capacitor to PGND; optional series resistor controls MOSFET dV/dt
10 OUT	High-current gate driver output	1 A peak totem-pole; 1.0 V low / 10 V high at 200 mA; 13 V clamp protects against inductive kickback
11 PGND	Power ground return	Separate from SGND to avoid noise coupling into control loop; ties to transformer primary return
12 SGND	Signal ground reference	Reference for VREF, VFB, COMP, SS, DIS; must be star-connected near IC for noise immunity
13 ISEN	Current sense input	Monitors primary current via sense resistor; 100 ns internal blanking prevents false triggering on switch turn-on
14 DIS	Latched disable input	Logic-high (>2.6 V) forces shutdown; must not float; tie to SGND if unused
15 DC-LIM	Duty cycle limiter select	Connect to VREF → 50% max duty; floating/grounded → full range (0–93%)
16 ST-BY	Standby mode control	Resistor to RCT sets standby threshold; connect to VREF or float if unused; enables automatic fosc→fSB transition

Key Features

Feature	Design Value
Programmable soft-start	14–26 µA charge current enables millisecond-scale ramp control of COMP voltage to limit inrush
Auto-adaptive standby mode	Reduces oscillator frequency under light load by monitoring VCOMP, cutting switching losses without sacrificing heavy-load performance
Integrated 100 ns leading-edge blanking	Suppresses false overcurrent trips during MOSFET turn-on, enabling reliable use of low-value sense resistors
Hiccup-mode overcurrent protection	Replaces latch-off with periodic restarts (Thic ≈ 4.5·(1/ISSC + 1/ISSD)·Css), maintaining thermal control during sustained faults
IN/OUT synchronization capability	Supports master/slave operation across multiple controllers, eliminating beat frequencies in multi-channel PSUs
Full-cycle PWM logic with double-pulse suppression	Prevents erroneous multiple switching events per oscillator period, ensuring stable duty cycle control

Applications

AC-DC Adapter

Industrial SMPS

Use Scenario: 12 V/3 A universal-input offline adapter for consumer electronics with <50 mW no-load consumption requirement.

IC Role / Device Role / Timing Role: Primary-side PWM controller managing transformer primary current, regulating output via optocoupler feedback to VFB, and entering standby mode below 10% load.

Use Value: Achieves <120 µA start-up current and auto-reducing fosc cuts light-load losses by >40% versus fixed-frequency alternatives.

Use Scenario: 24 V/10 A industrial power supply with overvoltage lockout and remote enable/disable functionality.

IC Role / Device Role / Timing Role: Core controller implementing current-mode regulation, using DIS pin for hardware OVP shutdown and SYNC pin for system-level clock alignment.

Use Value: Latched disable ensures fail-safe shutdown; 1 A gate drive eliminates external buffer stages, reducing BOM count and layout area.

LED Driver

Telecom DC-DC Module

Use Scenario: Constant-current LED driver for street lighting, operating from 300–400 VDC bus with analog dimming interface.

IC Role / Device Role / Timing Role: Flyback controller modulating peak primary current via DC pin voltage to adjust LED current; uses VREF as dimming reference source.

Use Value: Programmable 0–93% duty cycle enables wide dimming range; 5.0 V ±1.5% VREF ensures stable dimming reference across temperature.

Use Scenario: Isolated 48 V to 5 V/3 A telecom module requiring tight output regulation and EMI compliance.

IC Role / Device Role / Timing Role: Primary controller synchronizing to system clock via SYNC pin to reduce conducted EMI peaks; uses soft-start to meet inrush limits.

Use Value: IN/OUT sync enables deterministic switching harmonics; 100 ns blanking allows use of 50 mΩ sense resistors, minimizing conduction loss.

Equivalent & Alternatives

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

Alternative Part	Technical Difference	Application Difference	Selection Advice
UC3844BD1R2G	Fixed 52 kHz frequency, no standby mode, 1 A output, no sync pin, no programmable duty cycle limit	Suitable for cost-sensitive, fixed-frequency designs without light-load optimization needs	Select when simplicity and legacy compatibility outweigh adaptive efficiency features
TL3845P	Higher start-up current (1 mA), no soft-start, no standby, no sync, 200 mA output drive (requires external buffer)	Fits basic flyback designs where gate drive strength and light-load behavior are secondary	Choose only for non-critical, low-power applications where BOM cost is paramount

Compared with UC3844BD1R2G and TL3845P, the E-L5991AD uniquely combines programmable standby frequency reduction, 1 A integrated gate drive, and IN/OUT synchronization-enabling higher efficiency across load range and lower EMI in multi-rail systems without external components.

Availability

E-L5991AD is available at Aetrix Electronics and suitable for AC-DC adapters, industrial SMPS, LED drivers, and telecom DC-DC modules requiring stable component supply, long-term lifecycle support, and consistent parametric performance across temperature and voltage ranges.

Supply support for E-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 technologies, with broad manufacturing scale and automotive-grade quality systems.

The L5991 series belongs to ST's MultiPower BCD technology product line, designed specifically for high-voltage, high-efficiency primary-side switching controllers in offline and isolated DC-DC power conversion.

FAQ

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

The ST-BY pin enables automatic standby mode by connecting an external resistor to RCT. When VCOMP falls below 2.5 V, the IC reduces oscillator frequency to minimize light-load losses. If unused, ST-BY must be tied to VREF or left floating-never grounded. Configuration details and timing equations are provided in Figures 21 and 23 of the datasheet.

How does the hiccup-mode overcurrent protection operate?

Hiccup mode activates when ISEN exceeds 1.2 V for longer than the minimum on-time, triggering a full shutdown followed by soft-start restart. The hiccup period Thic ≈ 4.5·(1/ISSC + 1/ISSD)·Css ensures thermal safety during sustained faults. Unlike latch-off, it permits automatic recovery once the overload clears, supporting robust field operation.

Can the E-L5991AD synchronize to an external clock, and what are the voltage requirements?

Yes-pin 1 (SYNC) operates in slave mode with 1 V low / 3.5 V high logic thresholds and ≤0.5 mA input current. For reliable synchronization, the external master clock must exceed the programmed fosc by 10–20% to prevent instability. Internal 600 µA pull-down ensures defined state during startup.

What is the maximum recommended value for the soft-start capacitor (Css)?

Css should be selected to achieve a soft-start time (Tss) in the millisecond range-typically 1–10 ms-based on Tss ≈ 3·Rsense·IQpk/(ISSC·Css). Values above 100 nF risk excessive start-up delay and reduced fault response speed; ST recommends 10–47 nF ceramic capacitors with X7R dielectric for stability and low ESR.

E-L5991AD Specifications

Product attributes: Attribute value

Manufacturer:: STMicroelectronics

Series:: -

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

Packaging:: Tube

Product Status:: Obsolete

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

E-L5991AD FAQ

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

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

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

3.What payment methods are accepted for E-L5991AD?

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

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for E-L5991AD?

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

Once your E-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 E-L5991AD?

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

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

All E-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 E-L5991AD meets industry standards.

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

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

Return procedure for E-L5991AD:

1.Submit a request within 90 days.

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

Tech Hub

2026-08-21 What Is an LED Driver? Types, Circuits, Dimming, and Selection

An engineering guide to LED driver operation, constant-current and constant-voltage outputs, linear and switching topologies, dimming, IC selection, calculations, replacement compatibility, and fault c…

2026-08-18 Operational Amplifier (Op Amp): Basics, Configurations, Feedback and Applications

Operational amplifier guide covering op amp basics, feedback, ideal vs real op amps, common configurations, buffer circuits, offset, bias current, gain-bandwidth, slew rate, rail-to-rail limits and sel…

2026-08-14 Jumper Cables: How to Use, Connect and Choose Them Safely

Jumper cables guide covering safe connection order, red and black clamp placement, final ground connection, cable gauge, length, clamp quality, copper vs CCA cables, jump starter comparison and battery…

2026-08-11 LDO Regulator: Dropout Voltage, Noise, PSRR and Power Dissipation

LDO regulator guide covering low dropout voltage, power dissipation, thermal design, PSRR, output noise, capacitor stability, adjustable LDO circuits, LDO vs buck converter and datasheet selection chec…

2026-08-06 Conditional Access Module: CAM, CI/CI+ and DVB Security

Conditional Access Module guide covering CAM meaning, CI/CI+ interface, smart card authorization, DVB security workflow, TV and set-top box compatibility, internal electronics, ESD protection, connecto…

2026-08-03 Electronic Component Obsolescence: EOL Risks, Replacement Options and Last-Time Buy Strategy

Guide to electronic component obsolescence covering EOL risk, PCN/PDN notices, last-time buy planning, replacement options, form-fit-function validation, counterfeit risk and BOM lifecycle management.

2026-07-29 18650 Battery: Voltage, Capacity, Charging and Pack Design

18650 battery guide covering lithium-ion cell basics, 3.6V/3.7V voltage, 4.2V charging, mAh and Wh capacity, protected cells, chargers, BMS, series-parallel packs, holders, welding and sourcing checks.…

2026-07-27 Hall Effect Sensor: Working Principle, Types, Circuits and Applications

Hall effect sensor guide covering working principle, linear and digital sensors, Arduino circuits, current sensing, speed detection, automotive applications, A3144 examples, signal filtering and datash…

2026-07-20 Product Change Notification (PCN) in Electronic Components: Meaning and Supply Chain Response

Product Change Notification guide for electronic components, covering PCN meaning, PCN vs PDN/EOL, common change types, risk levels, form-fit-function review, engineering validation, BOM control, LTB/L…

2026-07-19 Blend Door Actuator: Symptoms, Location, Reset and Replacement Guide

A practical guide to blend door actuators, covering HVAC function, symptoms, location, AC and heater issues, reset and calibration, replacement cost, electrical diagnosis, compatibility checks, and rep…