This is a target, not a predicted board impedance or capacitor recommendation. Establish the frequency range from the device requirements and evaluate VRM, package, planes, capacitors, ESR and ESL separately. TI PDN analysis.
First-order target: allocated dynamic droop divided by actual load-current step. A flat target does not by itself establish transient compliance.
Target Impedance (Z_target):
$$ Z_{target} = \frac{V_{dd} \times (p/100)}{\Delta I} $$
Where $p$ is the entered dynamic droop percentage and $\Delta I$ is the actual transient current step.