1.6.11. Assessing How Much Total Capacitance Might be Required
Changing the PDN Tool Decoupling Mode from Auto to Manual allows you to enter any number of capacitors instead of limiting you to a maximum of 301. This is useful not only for implementing your own custom scheme, but also to estimate how much total capacitance is required to meet the target impedance with your PCB. For example, by entering 99999 high-frequency 22nF capacitors, you can see that Feffective does not increase much. It is very difficult to optimize the PDN any further even with this unrealistic number of capacitors. In this example we switch back to Auto decoupling mode.
In this case you can re-estimate and reduce where possible your power requirements, or you can estimate your Core Clock Frequency and Current Ramp Up Period parameters for the VCC supply.
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