What 900 ohms at 100 MHz means on a power line
The TDK ACM4520V-901-2P-T00 is a two-line common-mode filter from the ACM-V series, rated for 900 ohms impedance at 100 MHz. That impedance peak is where conducted EMI from switching regulators and digital clocks tends to radiate — the filter knocks down common-mode noise on the power rail without affecting the differential signal or DC current. Rated for 1.2 A continuous with a maximum DC resistance of 60 milliohms, the self-heating at full load stays under 90 mW — negligible for the 4.7 mm × 4.5 mm package. The 50 V DC rating covers 12 V, 24 V, and 48 V automotive and industrial rails with margin.
Qualified to AEC-Q200, the automotive passive-component stress standard. It fits under-hood electronics, engine-control modules, and transmission controllers where the ambient sees 105°C plus self-heating.