Hi:
in the below equation(1) , how the 2V comes? isn't it 40V?
2.2.1.2 Power Loop Capacitors
High-frequency capacitors for the power loop must provide currents in excess of 60 A with a rise time of ≈
300 ps (200 A/ns). The inductance of the loop is the main limiting element when dealing with those
speeds. The capacitors must be selected to allow for the maximum bus voltage. These capacitors must
provide both enough charge to sustain the current and a minimal inductive path.
X7R or better material is needed to provide stability and low ESR; a mix of 0603 and 0805 is necessary,
where the smaller capacitors are in the closest proximity to the power loop and the 0805 are adjacent to
those first capacitors. These materials are preferred if low-inductance, wide-body packages become
available.
The total value for the capacitance depends on the pulse repetition and pulse duration—in this case, a 1-
MHz repetition frequency for a 60-A, 1-ns pulse and a 40-V bus. To ensure the peak current is reached,
do not let the capacitor bank discharge more than 5% during the first half of the pulse.
( 60A x 1ns )/2V = 30-nF capacitance. (1)
thanks
Zhang
