The <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> Resonant converter is widely used in on-board charger applications for its high efficiency. However, conventional <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> converter with pulse-frequency-modulation suffers from a wide switching frequency range for realizing constant current (CC) and constant voltage (CV) charges. To address this problem, different from the traditional solution, a novel <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCL</i> resonant converter operating at a fixed resonant frequency with inherent CC and CV output characteristics is proposed in this letter. In the proposed concept, the CC and CV charges are accomplished by the special <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCL</i> tank. With the increasing of battery voltage during charging process, the resonant tank of the proposed converter is equal to the conventional <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCL</i> tank and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> tank for CC mode and CV mode, respectively. Thus, the sensing and control circuits are canceled while the wide zero-voltage-switching operation for primary switches and zero-current-switching for secondary diodes still be maintained. Therefore, the fixed resonant frequency operation, high efficiency, high reliability, and low cost are key features of the proposed converter. A 1-kW prototype with 400 V input and 250–400 V output is built and tested. The full load efficiency of 96.7% and higher than 96% for the CC mode were both achieved. The experimental results demonstrate the advance and validity of the proposed converter.