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STMicroelectronics L5991
- Part No.:
- L5991
- Manufacturer:
- STMicroelectronics
- Category:
- AC DC Converters, Offline Switches
- Package:
- 16-DIP (0.300", 7.62mm)
- Datasheet:
-
L5991.pdf
- Description:
- IC OFFLINE SWITCH MULT TOP 16DIP
- Quantity:
- Payment:
- Shipping:
Inventory:1,365
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Product details
Overview
L5991 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 0–100% duty cycle, and integrated standby mode with oscillator frequency reduction under light load.
For engineers reviewing the L5991 datasheet, L5991 pinout, L5991 application, or L5991 equivalent, this device supports precise duty-cycle control, internal 100 ns leading-edge blanking, latch-type overcurrent protection with hiccup-mode restart, IN/OUT synchronization, and dual-supply architecture (VCC for signal, VC for power stage) in DIP16/SO16 packages.
Technical Context
The L5991 implements fixed-frequency current-mode control using a sawtooth oscillator (pin 2) synchronized via pin 1, with duty cycle set by analog voltage on pin 3 (0–3.2 V) and limited to 50% when pin 15 is tied to VREF. Its error amplifier (pins 5–6) drives PWM logic directly, enabling fast transient response and loop stability across wide load ranges.
Standby operation is triggered by monitoring VCOMP (pin 6): when VCOMP falls below VT1 = 2.5 V (falling), oscillator frequency drops to fSB; recovery occurs at VT2 = 4.0 V (rising), with hysteresis preventing chatter. Internal 100 ns blanking on ISEN (pin 13) suppresses noise during MOSFET turn-on, while pulse-by-pulse current limiting and latch-off hiccup mode provide robust fault handling.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VREF Output | 5.0 V ±1.5% @ 25°C - stable reference for feedback and timing circuits |
| Switching Frequency | Up to 1 MHz - enables compact magnetics and high-power-density designs |
| Start-up Current | <120 µA - minimizes losses in high-resistance startup networks |
| Output Drive | 1 A peak sink/source - directly drives gate of power MOSFET without external buffer |
| Current Sense Threshold | 1.2 V typical - sets precise pulse-by-pulse current limit for primary-side protection |
| UVLO Hysteresis | 5 V ON / 10 V OFF with 4.5 V hysteresis - prevents oscillation near turn-on threshold |
| Leading Edge Blanking | 100 ns internal - eliminates false overcurrent trips during MOSFET turn-on transients |
| Soft Start Charge Current | 20 µA typical - controls ramp rate of SS capacitor for controlled output voltage rise |
Pinout & Package
Available in DIP16 and SO16 packages per ordering codes L5991/L5991A (DIP16) and L5991D/L5991AD (SO16). Thermal resistance: 80 °C/W (DIP16), 120 °C/W (SO16).
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 SYNC | In/Out synchronization interface | Master: outputs 4 V sync pulses; Slave: edge-triggered input for external clock alignment |
| 2 RCT | Oscillator timing node | Connects external CT, RA, RB to set fosc (RA//RB) and fSB (RA only) independently |
| 3 DC | Duty cycle control input | 0–3.2 V analog input sets max duty cycle from 0% to 100%; <1 V disables output |
| 4 VREF | 5 V reference output | ±1.5% accuracy; supplies timing, feedback, and external circuitry up to 10 mA |
| 5 VFB | Error amp inverting input | Compares optocoupler feedback to internal 2.5 V reference for closed-loop regulation |
| 6 COMP | Error amp output | Drives PWM comparator; monitored for standby activation and compensation network connection |
| 7 SS | Soft-start capacitor node | 20 µA internal charge current ramps control voltage linearly to prevent inrush |
| 8 VCC | Signal supply rail | UVLO at 7.8–9 V (L5991); internal 25 V Zener clamp protects against overvoltage |
| 9 VC | Power stage supply | Separate rail for driver output; decoupled to PGND to sustain pulsed gate currents |
| 10 OUT | High-current gate driver output | 1 A peak drive; low 1.0 V VOL @ 250 mA ensures strong MOSFET turn-on |
| 11 PGND | Power ground return | Low-inductance path for switch current; isolated from SGND to reduce noise coupling |
| 12 SGND | Signal ground reference | Reference for VREF, VFB, COMP, SS; must be star-connected near pins 4, 5, 6, 7, 12 |
| 13 ISEN | Current sense input | 100 ns blanked; 1.2 V threshold triggers hiccup mode on sustained overcurrent |
| 14 DIS | Latched disable input | 2.5 V threshold; ties to SGND if unused; used for OVP or system-level shutdown |
| 15 DC-LIM | Duty cycle limiter select | Tie to VREF → 50% max duty; floating → no limit; enables topology-specific safety margins |
| 16 ST-BY | Standby mode control | Resistor-to-RCT sets standby threshold; reduces fosc under light load to cut switching losses |
Key Features
| Feature | Design Value |
|---|---|
| Programmable dual-frequency oscillator | fosc and fSB set independently via RA/RB/CT - optimizes efficiency across full load range |
| Fully latched PWM logic with double-pulse suppression | Prevents multiple switching events per cycle - ensures clean gate drive and EMI control |
| Integrated hiccup-mode overcurrent protection | Auto-restart after fault clearance - maintains regulation without manual reset or latch-off |
| Separate VCC and VC supplies | Isolates signal integrity from power-stage noise - improves stability and reduces coupling |
| IN/OUT synchronization capability | Enables multi-controller parallel operation or master-slave coordination - essential for multi-output or interleaved designs |
| 100% duty cycle support | Enables zero-voltage-switching (ZVS) topologies and extended conduction in low-Vin conditions |
Applications
| AC-DC Adapter | Industrial SMPS |
|---|---|
Use Scenario: 12 V/3 A universal-input offline adapter for IoT gateways. IC Role / Device Role / Timing Role: Primary-side PWM controller regulating output via optocoupler feedback; sets 500 kHz switching and 65% max duty cycle. Use Value: Standby mode cuts no-load consumption to <300 µA; soft-start prevents inrush into bulk cap. | Use Scenario: 24 V/10 A industrial power supply with OVP and brownout protection. IC Role / Device Role / Timing Role: Core controller managing primary MOSFET drive, current sensing, and UVLO/overvoltage shutdown. Use Value: 1 A gate drive eliminates external buffer; hiccup mode sustains operation during intermittent short circuits. |
| LED Driver (Flyback) | Telecom DC-DC Module |
Use Scenario: Constant-current 48 V LED string driver with dimming interface. IC Role / Device Role / Timing Role: Primary controller implementing CC regulation via secondary-sense feedback; uses DIS pin for PWM dimming enable. Use Value: Programmable duty cycle allows precise current scaling; 100 ns blanking rejects LED-string switching noise. | Use Scenario: Isolated 48 V to 5 V/3 A telecom brick with tight hold-up time. IC Role / Device Role / Timing Role: High-frequency (800 kHz) flyback controller with sync input locked to system clock bus. Use Value: SYNC pin enables phase alignment across multiple rails; separate VC supply isolates gate drive from digital noise. |
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 |
|---|---|---|---|
| UC3844B | Fixed 52 kHz frequency; no standby mode; 200 mA output drive; no sync or soft-start charge control | Lacks light-load efficiency optimization and high-current gate drive - unsuitable for >5 W adapters | Select only for cost-sensitive, low-power, fixed-frequency legacy designs without hiccup protection |
| TL3845P | Higher start-up current (1 mA); no programmable duty cycle; no internal blanking; 500 mA output | Requires external blanking circuit; cannot support >10 W without gate driver; no frequency reduction in standby | Choose only where BOM count reduction outweighs efficiency and protection trade-offs |
Compared with UC3844B and TL3845P, the L5991 delivers superior light-load efficiency via standby frequency scaling, eliminates external blanking components, supports higher power with 1 A drive, and integrates hiccup-mode fault recovery - making it optimal for modern energy-efficient flyback converters.
Availability
L5991 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-lifecycle availability, and consistent parametric performance across temperature and line variations.
Supply support for L5991 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 L5991 belongs to ST's MultiPower BCD60II product line - engineered for high-voltage, high-efficiency offline power conversion with integrated protection and adaptive control features.
FAQ
What is the difference between L5991 and L5991A?
The L5991A features tighter UVLO thresholds (7.8 V turn-on / 7.0 V turn-off) versus L5991 (9 V / 10 V), optimized for lower-voltage auxiliary supplies. Both share identical pinout, functionality, and electrical specs except UVLO hysteresis and start-up current tolerance - L5991A guarantees ≤75 µA start-up current vs. ≤120 µA for L5991.
How does the standby function reduce power loss?
Under light load, the L5991 monitors VCOMP (pin 6); when it falls below 2.5 V, the oscillator switches from fosc to lower fSB (e.g., 100 kHz instead of 500 kHz), cutting switching losses - which dominate no-load dissipation in flyback converters - while retaining full regulation capability upon load increase.
Can L5991 drive a SiC MOSFET directly?
No - the L5991's 1 A peak output and 10 V VOH are rated for standard silicon MOSFETs. Driving SiC devices requires higher gate drive strength, negative turn-off bias, and faster slew rates. An external gate driver (e.g., STGAP2SIC) is required for SiC compatibility.
Why is separate VCC and VC supply necessary?
VCC powers low-noise analog circuitry (error amp, references, logic); VC supplies the high-current output stage. Separating them prevents switching transients on VC from modulating reference or feedback nodes - preserving loop stability and reducing EMI susceptibility in sensitive regulation paths.
L5991 Specifications
- Product attributes
- Attribute value
- Manufacturer:
- STMicroelectronics
- Series:
- -
- Package/Case:
- 16-DIP (0.300", 7.62mm)
- Packaging:
- Tube
- Product Status:
- Obsolete
- Output Isolation:
- Isolated
- Internal Switch(s):
- No
- Voltage - Breakdown:
- -
- Topology:
- Boost, Flyback
- Voltage - Start Up:
- 15 V
- Voltage - Supply (Vcc/Vdd):
- 10V ~ 20V
- Duty Cycle:
- 93%
- Frequency - Switching:
- Up to 1MHz
- Power (Watts):
- -
- Fault Protection:
- Current Limiting, Over Voltage
- Control Features:
- Frequency Control, Soft Start, Sync
- Operating Temperature:
- -40°C ~ 150°C (TJ)
- Grade:
- -
- Qualification:
- -
- Supplier Device Package:
- 16-DIP
- Mounting Type:
- Through Hole
L5991 FAQ
1.How can I place an order for L5991 through Aetrix?
Please submit a Request for Quotation (RFQ) for L5991 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 L5991 reliable?
The price and inventory of L5991 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for L5991 is usually 5 days.
3.What payment methods are accepted for L5991?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for L5991 transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for L5991?
L5991 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your L5991 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 L5991?
For technical support, including L5991 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your L5991 requirements.
6.How does Aetrix verify that L5991 is sourced from the original manufacturer or authorized distributors?
All L5991 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 L5991 meets industry standards.
7.What is the process for return or replacement of L5991?
All L5991 units undergo pre-shipment inspection (PSI). If there is an issue with L5991, 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 L5991 part is unused and in its original packaging.
Return procedure for L5991:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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