The FAN7621S is a pulse frequency modulation controller for high-efficiency half-bridge resonant converters. Offering everything necessary to build a reliable and robust resonant converter, the FAN7621S simplifies designs and improves productivity, while improving performance. The FAN7621S includes a high-side gate-drive circuit, an accurate current-controlled oscillator, frequency-limit circuit, soft-start, and built-in protection functions. The high-side gate-drive circuit has a common-mode noise cancellation capability, which guarantees stable operation with excellent noise immunity. Using the zero-voltage-switching (ZVS) technique dramatically reduces the switching losses and significantly improves efficiency. The ZVS also reduces the switching noise noticeably, which allows a small-sized Electromagnetic Interference (EMI) filter. The FAN7621S can be applied to various resonant converter topologies; such as series resonant, parallel resonant, and LLC resonant converters.