LLC resonant controller features synchronous rectification

The FAN7688 incorporates Fairchild’s innovative Charge Current Control Technology, which uniquely enables it to utilise current mode control, as opposed to voltage mode control, which is traditionally used in other LLC solutions. The industry’s first and only LLC resonant controller with current mode control and SR (according to Fairchild), the FAN7688 allows for tighter and faster output regulation against load transients and also simplifies the control loop, which makes designing it into power supplies easier than traditional LLC resonant controllers. Additionally, the FAN7688’s Adaptive Dual Edge Secondary Side Synchronous Rectifier Control ensures high reliability and stable SR operation of both load and line transients.

The FAN7688’s current mode control is a technique based on a charge control providing a better control-to-output transfer function of the power stage simplifying the feedback loop design while allowing true input power limit capability. Closed-loop soft-start allows a monotonic rising of the output voltage regardless of load condition. The dual edge tracking adaptive dead time control minimises the body diode conduction time, thus maximising efficiency.

The FAN7688 incorporates multiple features to ensure high efficiency in power supply applications: typically 97% for 400V input and 12V output applications. The efficiency of the FAN7688 is also enhanced by its comprehensive set of protection functions, including over-load protection, over-current protection, output-short protection and over-voltage protection.

Gaurang Shah, Senior Vice President, Analog Power Group, Fairchild Semiconductor, commented: “Our FAN7688 is another industry first from Fairchild and an ideal solution for manufacturers requiring offline solutions that improve the efficiency of the power supplies within their products while enabling highly reliable and robust control of secondary and primary MOSFETs. The best-in-class protection features of the FAN7668 are complemented by its outstanding robustness, much of which comes from the direct drive of the secondary side rectification MOSFETs.”

The FAN7688 is available now along with two evaluation boards, the 306W FEBFAN7668 and the 250W FEBFAN7688A (recommended for designers who want to evaluate the LLC in detail).