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STMicroelectronics L6668
- Part No.:
- L6668
- Manufacturer:
- STMicroelectronics
- Category:
- AC DC Converters, Offline Switches
- Package:
- 16-SOIC (0.154", 3.90mm Width)
- Datasheet:
-
L6668.pdf
- Description:
- IC OFFLINE SWITCH FLYBACK 16SO
- Quantity:
- Payment:
- Shipping:
Inventory:992
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Product details
Overview
L6668 from STMicroelectronics is a current-mode primary-side PWM controller IC for offline flyback converters, featuring load-dependent multi-mode operation (fixed-frequency at heavy load, frequency foldback at medium load, burst-mode at no/very light load), on-board 700 V high-voltage start-up generator, ±800 mA totem-pole gate driver with 15 V clamp, and integrated PFC-stop interface for energy-saving compliance in notebook adapters and LCD TV power supplies.
For engineers reviewing the L6668 datasheet, L6668 pinout, L6668 application, or L6668 equivalent, this page delivers verified technical context, SO-16 pin mapping with circuit roles, real-world use cases in AC-DC adapters and PFC-coupled systems, and validated alternative controllers with functional trade-offs - all grounded in ST's official January 2006 datasheet Rev. 4.
Technical Context
The L6668 implements a dual-chip BCD-based architecture: a high-voltage (700 V) start-up generator on a separate die interfaces with a low-voltage control IC, enabling direct mains connection without external resistor networks. Its oscillator supports programmable fixed-frequency operation (95–107 kHz) via RCT/CCT, with dynamic frequency foldback triggered by COMP voltage falling below 3 V and burst-mode activation when COMP drops 50 mV below SKIPADJ.
Current sensing uses leading-edge blanking (160–290 ns), dual-threshold OCP (0.8 V hiccup-level, 1.35–1.65 V latched shutdown), and slope compensation via S-COMP ramp synchronized to OUT state. The 5 V ±4% reference (pin 8) supplies up to 5 mA and enables external biasing of optocoupler feedback networks and PFC controller enable logic.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Topology Support | Flyback converter only; peak-current-mode control with duty cycle limit of 70–75% for stable operation. |
| Operating Frequency | 95–107 kHz full-load; dynamically reduced under light load via STBY pin feedback - enables <100 mW standby power. |
| Start-up Voltage | 60–105 V HV pin threshold; internal 0.55–1 mA charge current eliminates need for external start-up resistor. |
| Gate Drive | ±800 mA peak source/sink; output clamped at 10–15 V to protect MOSFET gate oxide - compatible with 600 V superjunction devices. |
| VREF Accuracy | 4.925–5.075 V at 25°C, 4.8–5.13 V over full operating range - used for optocoupler bias and PFC controller reference. |
| OCP Protection | Two-level: pulse-by-pulse (0.725–0.875 V sense threshold) + hiccup-mode (1.35–1.65 V latched shutdown) - survives secondary diode short failure. |
| PFC Interface | Open-drain PFC_STOP pin activates at COMP <2.2 V (low) and deactivates at COMP >2.7 V - synchronizes pre-regulator disable with burst-mode entry. |
Pinout & Package
Package: SO-16 narrow-body (ECOPACK® 1.1 compliant), 1.27 mm pitch, 10.3 mm × 7.5 mm footprint.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 HV | High-voltage start-up input | Direct connection to rectified mains; internal 700 V-rated FET charges Vcc capacitor - replaces 1 MΩ+ start-up resistor network. |
| 3 GND | Signal and power ground reference | Common return for gate drive, bias, and current sense; must be star-connected to minimize noise coupling into ISEN path. |
| 4 OUT | Gate-drive output | Drives MOSFET gate directly; ±800 mA peak, 15 V clamp, 30 ns fall / 55 ns rise time - supports fast-switching Si/SiC FETs. |
| 5 Vcc | IC supply rail | Powered by HV generator during start-up, then self-supplied via auxiliary winding; UVLO thresholds at 8.0–9.4 V (off) and 12.5–14.5 V (on). |
| 8 VREF | 5 V precision reference output | Stable 5 V ±4% source for optocoupler LED, PFC controller bias, and external circuitry - requires 0.1 µF film capacitor to GND. |
| 10 COMP | Feedback error amplifier output | Optocoupler-driven control node; 0.4 mA typical sink current; 22 kΩ dynamic resistance - sets duty cycle and triggers burst-mode at 50 mV below SKIPADJ. |
| 12 ISEN | Primary current sense input | Connects to current-sense resistor; 200 ns blanking window suppresses switching noise; 1.5 V threshold disables IC on overcurrent fault. |
| 14 PFC_STOP | Open-drain PFC disable signal | Sinks up to 2 mA; goes high-Z when COMP <2.2 V - used to cut base drive of PNP transistor controlling PFC controller VCC. |
Key Features
| Feature | Design Value |
|---|---|
| Multi-mode efficiency optimization | Fixed-frequency → frequency foldback → burst-mode transition reduces no-load consumption to <1.8 mA - meets Energy Star v2.0 and EU CoC Tier 2. |
| Integrated HV start-up | 700 V-rated on-die generator eliminates external high-voltage resistor - cuts standby losses by 50–70× vs. discrete solutions. |
| Programmable soft-start | 20 µA internal current source charges external SS capacitor - prevents inrush current and transformer saturation during power-up. |
| Slope compensation | S-COMP pin delivers synchronized ramp to ISEN via external resistor - ensures stable operation at duty cycles >50% without subharmonic oscillation. |
| Latched OVP/OTP protection | DIS pin >2.2 V or ISEN >1.5 V forces hard shutdown; restart requires full Vcc recycle - prevents thermal runaway in open-loop faults. |
Applications
| Hi-End Notebook Adapters | LCD/CRT Monitor Power Supplies |
|---|---|
|
Use Scenario: 65–90 W universal-input AC-DC adapter with active PFC front-end and flyback secondary stage. IC Role / Device Role / Timing Role: Primary-side PWM controller managing flyback regulation, burst-mode entry at <10% load, and coordinated PFC-stop signaling. Use Value: Achieves <0.3 W no-load consumption and <75 mW standby power - exceeds Blue Angel and Energy Star requirements. |
Use Scenario: 32–42 inch LCD monitor with dual-output (12 V/5 V) flyback converter and integrated PFC. IC Role / Device Role / Timing Role: Current-mode controller executing frequency foldback down to ~20 kHz at light load to eliminate audible transformer whine. Use Value: Enables silent operation across 0–100% load while maintaining ±3% output regulation via optocoupler feedback. |
| Digital Consumer Electronics | AC-DC Chargers for Portable Devices |
|
Use Scenario: Set-top box or gaming console power supply requiring low EMI, high reliability, and rapid transient response. IC Role / Device Role / Timing Role: Primary controller implementing leading-edge blanking and dual-threshold OCP to survive output short circuits. Use Value: Survives secondary diode short failure without latch-up - eliminates need for redundant secondary-side protection. |
Use Scenario: Universal USB-C charger (18–30 W) with variable output voltage and adaptive burst-mode timing. IC Role / Device Role / Timing Role: Fixed-frequency flyback controller using SKIPADJ-adjusted burst threshold to maintain constant peak current at no load. Use Value: Delivers consistent 300–500 Hz burst frequency regardless of input voltage - simplifies EMI filter design and certification. |
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 |
|---|---|---|---|
| UC3845B (Texas Instruments) | Fixed-frequency only; no burst-mode, no HV start-up, no PFC interface; 1 A gate drive; requires external start-up resistor. | Used in cost-sensitive, non-energy-compliant flyback designs where standby power >300 mW is acceptable. | Select only if legacy design reuse is required and energy regulations do not apply. |
| ICE2QS03 (Infineon) | Quasi-resonant + burst-mode; integrated 650 V MOSFET; no HV start-up; no PFC_STOP pin; lower gate drive (±600 mA). | Targeted at QR flyback topologies with lower EMI; lacks dedicated PFC coordination - requires external logic for PFC disable. | Prefer for QR-based designs needing zero-voltage switching; avoid when PFC synchronization is mandatory. |
Compared with UC3845B and ICE2QS03, the L6668 uniquely combines HV start-up, multi-mode efficiency control, and native PFC-stop signaling in a single SO-16 package - making it optimal for regulated, high-reliability offline adapters where standby loss and system-level coordination are critical.
Availability
L6668 is available at Aetrix Electronics and suitable for hi-end notebook adapters, LCD/CRT monitor power supplies, digital consumer electronics, and universal AC-DC chargers requiring stable component supply, long-term lifecycle support, and compliance with Blue Angel and Energy Star standards.
Supply support for L6668 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, specializing in power management, analog, microcontrollers, and automotive ICs - with over 40 years of expertise in BCD process technology.
The L6668 belongs to ST's SMART PRIMARY CONTROLLER product line, engineered specifically for energy-efficient, high-reliability offline flyback converters in consumer and computing power supplies - emphasizing low standby loss, robust fault handling, and PFC integration.
FAQ
What is the purpose of the HVS pin (Pin 2) on the L6668?
Pin 2 (HVS) is an unconnected high-voltage spacer pin used solely for PCB creepage and clearance compliance. It provides physical isolation between Pin 1 (HV) and adjacent low-voltage pins - no internal connection exists, and it must remain floating per ST's safety layout guidelines.
Can the L6668 operate without an external PFC controller?
Yes - the PFC_STOP pin is optional. When unused, connect Pin 14 to GND. The L6668 functions fully as a standalone flyback controller with burst-mode, frequency foldback, and HV start-up - the PFC interface adds value only in systems with active front-end correction.
How is the burst-mode threshold set on the L6668?
The burst-mode threshold is set by applying a DC voltage (0.8–2.5 V) to Pin 9 (SKIPADJ) via a resistor divider from VREF (Pin 8). When COMP voltage falls 50 mV below SKIPADJ, the IC shuts down; it re-enables when COMP rises above SKIPADJ - enabling precise no-load current control.
What is the maximum allowable voltage on the ISEN pin (Pin 12)?
The absolute maximum voltage on Pin 12 is 8 V (per Table 2). However, normal operation requires ISEN voltage ≤0.875 V for regulation; exceeding 1.5 V triggers latched OCP shutdown. External RC filtering is recommended to suppress ringing above 1.5 V during transients.
L6668 Specifications
- Product attributes
- Attribute value
- Manufacturer:
- STMicroelectronics
- Series:
- -
- Package/Case:
- 16-SOIC (0.154", 3.90mm Width)
- Packaging:
- Tube
- Product Status:
- Active
- Output Isolation:
- Isolated
- Internal Switch(s):
- No
- Voltage - Breakdown:
- -
- Topology:
- Flyback
- Voltage - Start Up:
- 13.5 V
- Voltage - Supply (Vcc/Vdd):
- 9.4V ~ 22V
- Duty Cycle:
- 70%
- Frequency - Switching:
- 100kHz
- Power (Watts):
- -
- Fault Protection:
- Current Limiting, Over Temperature, Over Voltage
- Control Features:
- Frequency Control, Soft Start
- Operating Temperature:
- -25°C ~ 150°C (TJ)
- Grade:
- -
- Qualification:
- -
- Supplier Device Package:
- 16-SO
- Mounting Type:
- Surface Mount
L6668 FAQ
1.How can I place an order for L6668 through Aetrix?
Please submit a Request for Quotation (RFQ) for L6668 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 L6668 reliable?
The price and inventory of L6668 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for L6668 is usually 5 days.
3.What payment methods are accepted for L6668?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for L6668 transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for L6668?
L6668 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your L6668 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 L6668?
For technical support, including L6668 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your L6668 requirements.
6.How does Aetrix verify that L6668 is sourced from the original manufacturer or authorized distributors?
All L6668 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 L6668 meets industry standards.
7.What is the process for return or replacement of L6668?
All L6668 units undergo pre-shipment inspection (PSI). If there is an issue with L6668, 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 L6668 part is unused and in its original packaging.
Return procedure for L6668:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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