Critical Bandwidth for the Load Transient Response of Voltage Regulator Modules

Load-Line Regulation With Estimated Load-Current Feedforward: Application to Microprocessor Voltage Regulators

“…Under this control law, the voltage-loop unity gain bandwidth is (16) Indeed, for the case has been previously identified as a critical bandwidth which constrains the switching frequency choice [8], [16]. Analogously to Section III-B, we can combine (16) with the bandwidth stability constraint (3) to link the required output capacitance to the switching frequency (17) Clearly, the voltage-loop bandwidth requirement (16) and the associated output capacitor constraint (17) are more relaxed compared to those for load-line feedback control given in (9) and (10), respectively. However, here we have assumed infinite current-loop gain.…”

“…Variations of these linear control approaches are commonly adopted by industry, typically using fixed-frequency pulsewidth modulated (PWM) modulation [11]. With these techniques, the nominal system closed-loop bandwidth is tightly related to the output capacitor ESR time constant [8], [16]. With typical electrolytic capacitors having such a time constant on the order of 3-10 s, it is straightforward for this approach to work with conventional switching frequencies in the range of 200-500 kHz.…”

“…The bandwidth of converters with linear feedback control is limited by stability constraints linked to the switching frequency [8], [16]. Extending the bandwidth can result in cost and board area savings, since it can reduce the required number of capacitors [17].…”

“…Conventional load-line control, as used in microprocessor VR applications, sets the desired closed-loop impedance equal to the output capacitor ESR [4], [5]. While this approach works well with capacitor technologies with large ESR time constants , such as electrolytic capacitors, it is not applicable to small ESR time constant technologies, such as ceramic capacitors, due to their small capacitance per unit ESR [8], [16]. With ceramic capacitors, the capacitor size has to be chosen large enough so that it provides adequate ripple filtering and load transient support.…”

1.8-MHz, 48-V Resonant VRM: Analysis, Design, and Performance Evaluation

“…15, the rise time of the output filter inductor current is around five-six clock periods. If the response of the inductor current to the step change of the load current is approximated as a second-order system with the oscillation frequency close to the control loop bandwidth, the rise time of the inductor current can be approximated as a quarter of the oscillation period [6], i.e., 1 4 2 s. It should be noted in Fig. 15 that during the ramp-up of the inductor current, the increased error-amplifier voltage increases the phase shift of the SR control pulses with respect to the beginning of the switching cycle, increases, and more energy is stored in the resonant inductor.…”