UCC28600TDRQ1

The UCC28600TDRQ1 from Texas Instruments is an AEC-Q100 Grade 1 qualified quasi-resonant flyback controller in an 8-pin SOIC package. The TD denotes the SOIC-8 package, R denotes tape and reel, and Q1 confirms the automotive -Q1 product designation. The controller drives an external N-channel MOSFET in a flyback converter topology with three operating modes optimized for efficiency across the entire load range: (1) Quasi-Resonant (QR) mode at heavy loads, where the MOSFET turns on at the valley of the drain voltage ringing, minimizing turn-on switching losses; (2) Frequency Foldback (FF) mode at medium loads, where the switching frequency decreases linearly with decreasing load to maintain high efficiency; (3) Green-mode burst operation at light loads, where the controller skips switching cycles entirely, reducing average switching frequency and losses. The 25uA startup current allows use of a high-value startup resistor from the rectified AC line, minimizing standby power. The controller uses primary-side regulation via the auxiliary winding for output voltage feedback, eliminating the need for an optocoupler in non-isolated or simple designs. Comprehensive protection includes pulse-by-pulse overcurrent, overvoltage via VDD, and thermal shutdown.

The UCC28600TDRQ1 operates through five subsystems: (1) Quasi-Resonant Control: During QR mode, the controller monitors the drain voltage through the auxiliary winding. After the MOSFET turns off and the secondary current reaches zero (demagnetization), the drain voltage rings due to the resonance of the primary inductance and MOSFET capacitance. The controller detects the valley of this ringing and turns on the MOSFET at the lowest point, minimizing capacitive turn-on losses (Eoss). This valley-switching technique significantly reduces switching losses compared to hard-switched flyback converters. (2) Frequency Foldback: As the load decreases, the controller reduces the switching frequency from the QR maximum (up to 130kHz) down to 40kHz. This reduces switching losses proportionally with load, maintaining high efficiency. The output is regulated by modulating the on-time. (3) Green-Mode Burst: At very light loads, the controller enters burst mode: it performs a few switching cycles to charge the output above regulation, then stops switching entirely. During the off period, only the 3mA operating current is consumed. This achieves very low standby power consumption. (4) Primary-Side Regulation: The auxiliary winding voltage reflects the output voltage during the secondary conduction period. The controller samples this voltage to regulate the output, typically achieving +/-5% regulation. For tighter regulation, an optocoupler can be used with the FB pin. (5) Protection: Pulse-by-pulse current limiting through the CS pin, OVP via VDD pin, and thermal shutdown protect the converter from fault conditions.

• Automotive 12V battery to 5V/3A off-line power supply using QR flyback with valley switching for low EMI and high efficiency at 150W
• Industrial 24V output LED driver with quasi-resonant mode at full load and green-mode burst at standby for less than 0.5W no-load consumption
• Laptop adapter 19V/4A using frequency foldback for medium-load efficiency and primary-side regulation for simplified design without optocoupler
• Battery charger with pulse-by-pulse current limiting via CS pin and overvoltage protection via VDD for safe CC/CV operation