Kappa Switching DC-DC Converter with Continuous Input and Output Currents Achieving 86.7% Input Ripple Suppression and 16dB Peak EMI Reduction

To achieve high power efficiency for step-up and step-down conversions, switching DC-DC power converters are widely used. However, the high di/dt and dv/dt transitions from switching converter operation create unwanted EMI noise which injects into the input and ground bus and interferes with other systems. To mitigate this, this paper presents an isolated gate driver and double-NMOS based switching DC-DC converter -the Kappa converter which has both continuous input and output currents. With two inductors isolating both input and ground respectively as well as a minimized di/dt hot loop formed by a flying capacitor and two power switches, the Kappa buck and Kappa boost converters can be configured to achieve respective step-down and step-up voltage conversions. The Kappa buck converter, with one inductor connecting to input, has a continuous input current which can significantly reduce the input ripple, mitigate EMI noise and eliminate the need of bulky input EMI filters required by the conventional buck converter. Meanwhile, the entire load current is distributed between the two inductors to reduce DCR loss, but only two power switches are required compared to conventional two-phase buck converter. A Kappa buck converter with isolated gate driver is implemented to achieve a DC-DC conversion from 48V to 5V at an I
O
up to 5A. Compared to a conventional buck converter with same passive component values and operating conditions, this Kappa converter has an input ripple of 14mV, achieving 86.7% input ripple suppression and 16dB peak EMI noise reduction.