Isolated DC-DC converters and methods for operating the same are described herein. DC-DC converters include a driver that drives a primary winding of a transformer to transmit power to a secondary winding of the transformer across an isolation barrier. In some embodiments, a pair of symmetrical serial capacitors are provided between the driver and the primary winding of a resonant DC-DC converter with an on-chip transformer to slow down variations of a common mode voltage on the primary winding during operation. This in turn can suppress radiation emissions related to time variation rates of the common mode voltage and, and can also improve electromagnetic interference (EMI) performance of the DC-DC converter.