Issue link: https://iconnect007.uberflip.com/i/1359517
46 DESIGN007 MAGAZINE I APRIL 2021 tive component. Another illustration (Figure 2) shows a simplified schematic of a point-of- load, end-to-end power distribution network, where we explicitly identify series resistances and inductances. We can assume that in Figure 2 all induc- tances are side effects: parasitics of the planes, wires, traces, connectors, as well as the para- sitics of the capacitors. Note that in LTSPICE, inductors and capacitors can have parasitics assigned to the part and by doing so, instead of calling out separate circuit elements for those parasitics, will speed up the simulation. With several inductances both in the series and par- allel paths, together with the capacitances, we end up with a multitude of potential reso- nances that we all need to worry about. is circuit was simulated and analyzed in a previ- ous column [1] . To show the consequences of unexpected or accidental series inductance in the power distribution path, we can simplify the PDN circuit to a one-stage interface between the power source and power consumer with an L-C circuit. Figure 3 shows the circuit with its assumed component values. e current sources on the le represent the power con- sumer (load) and the entire power distribution network is simplified to a one-lump L-C cir- cuit. From the allowed voltage fluctuation and assumed transient current we get a 20-mOhm target impedance. Accordingly, the source Figure 2: LTSPICE schematics of a simple point-of-load PDN. Figure 3: LTSPICE schematics for a one-stage L-C PDN circuit with matched source and load.