TIDUET3 February   2021

 

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2.3.2 UCC25640X

An LLC resonant converter is one of the most widely used topologies for implementing medium- to high- power, isolated, DC/DC power stages in industrial power supplies. These converters are popular due to their ability to achieve soft-switching (ZVS turn on) for the high-voltage MOSFET and hence improving the overall efficiency of the system. The UCC25640x is a fully featured LLC controller. The UCC25640x includes a range of features designed to make LLC converter operation well controlled and robust. The part aims to unburden the LLC designer and allow mainstream applications to benefit from efficiency advantages of the LLC topology. This device uses hybrid hysteretic control to provide best-in-class line and load transient response. The control effort is approximately linear proportional to the average input current in one cycle. The control makes the open loop transfer function a first-order system so that it is very easy to compensate. The system is always stable with proper frequency compensation. Ensure that the LLC converter does not enter capacitive (ZCS) region during the low input voltage condition; otherwise, it could make damage to the system.

The UCC25640x with its ZCS avoidance feature can ensure that the system does not enter the ZCS region under all operating conditions and hence ensures the safety of the system. Apart from this, the power supplies typically need a tunable input or output voltage with a wide range. The UCC25640x provides a wide operating frequency range from 35 kHz to 1MHz to make it easier to design a wide output voltage range using an LLC converter. Its wide frequency range can reduce the PFC bulk capacitor required to meet the holdup time requirement in the industrial power supplies. With the integrated high- voltage gate drive, X-Cap discharge function, and additional output OVP, the UCC256401x reduces the amount of external discreet components required to implement a high-efficiency industrial PSU.