Coupled inductors improving the performance of the microprocessor VR (1999)
Coupled inductors can improve the performance of the microprocessor VR by: 1) Increasing the steady state inductance and reducing the transient inductance and, 2) Increase the VR bandwidth.
The steady state inductance is the equivalent inductance of coupled inductors which determines the VR phase current ripple and the VR efficiency. The transient inductance is the equivalent inductance of coupled inductors which determines the VR phase current slew rate when the duty cycle of the VR saturates. Through proper design of the coupled inductors, the steady state inductance of the VR can be increased and the transient inductance of the VR can be reduced. As a result, the efficiency of the VR is higher and the transient performance of the VR is faster.
The coupled inductors can also increase the bandwidth of the VR. The microprocessor VR is the DC-DC converter with current mode control. The sample and hold effect, which exists in the current model control, will limit the bandwidth of VR. Through coupling, the equivalent frequency of the sample and hold effect will be doubled (for two-phase coupled inductors). Therefore, the bandwidth of the VR can be increased.