900 ohms at 100 MHz — what that means on a power rail
The TDK ACM4520-901-2P-TL000 is a two-line common mode filter from the ACM series, rated for 900 Ohms impedance at 100 MHz. That impedance peak sits right where conducted EMI from switching regulators and digital clocks couples onto the DC bus — the filter presents a high series impedance to common-mode noise while letting the differential power current pass through with minimal loss. The 50 V DC rating covers most board-level power buses including 48 V telecom rails, so the voltage margin is not the limiting factor here — the 2 A current ceiling is the spec that governs the fit.