Fairchild introduces the industry's first current mode control

     Fairchild has introduced the FAN7688, an advanced LLC controller with synchronous rectification (SR) that provides very high efficiency for isolating DC-DC converters. The unique features and efficiency of the FAN7688 enable manufacturers to greatly improve the reliability and efficiency of power supplies for server, telecom, industrial, PC and TV applications.

     The FAN7688 uses Fairchild's innovative charging current control technology, which is unique in adopting current mode control, as opposed to voltage mode control in other traditional LLC solutions. As the industry's first and only LLC resonant controller with current mode control and synchronous rectification, the FAN7688 not only enables more accurate and faster output adjustment for rapid load changes, but also simplifies the control loop, making it easier to design and integrate into power systems than traditional LLC resonant controllers. In addition, the adaptive double-edge secondary synchronous rectification control method of the FAN7688 ensures high reliability and stable synchronous rectification operation during load and line transients.

     Gaurang Shah, senior vice president of Fairchild's Analog Power group, said: "Our new FAN7688, another industry first from Fairchild, is the ideal solution for manufacturers who need an offline solution to improve the power efficiency of their products while providing reliable control of both primary and secondary MOSFETs. The FAN7668's best-in-class protection is matched by its exceptional durability, thanks in large part to the direct drive of the secondary rectified MOSFETs."

     The current mode control of the FAN7688 is based on charge control technology, which provides a better power level control to the output transfer function, simplifying the feedback loop design while realizing the input power limiting function. Closed-loop soft start allows the output voltage to rise monotonically regardless of load conditions. The double edge tracking adaptive dead-time control function minimizes the on-time of the bulk diode and thus maximizes efficiency.

     The FAN7688 uses a variety of features to ensure high power efficiency, typically reaching 97% in 400V input and 12V output applications. The FAN7688 also has complete protection functions, which further improve its efficiency, including overload protection, overcurrent protection, output short circuit protection and overvoltage protection.