A Fast-Transient-Response Auxiliary Circuit with a Switched Capacitor for Voltage Regulator Modules

As the current step and slew rate of microprocessors increase, greater demands are placed on transient responses of voltage regulator modules (VRMs). In this article, a switched capacitor auxiliary circuit (SCAC) is proposed to enhance transient responses of VRMs. One end of the switched capacitor is connected to the VRM output voltage V_o, whereas the other end has a variable Voltage. When the load current changes, the switched capacitor’s variable end Voltage is adjusted, enabling rapid charge injection and absorption, thereby reducing V_o undershoot and overshoot. As a demonstration, a field programmable gate array (FPGA)-controlled SCAC prototype is implemented at the output of a 12V-0.9V 14-phase VRM. Transient tests are conducted with a load current step of 480 A, slew rate of 960 A/μs, and load current variable frequencies of 300 Hz to 1 MHz. The maximum overshoot and undershoot of the VRM were reduced from 190 mV to 95 mV and 142 mV to 80 mV, respectively, by implementing the SCAC, reducing the transient V_o change by 43%.