What this 0805 common-mode filter does on the line
The TDK ACM2012E-121-2P-T01 is a 2-line signal line EMI filter from the ACM-E series, packaged in an 0805 surface-mount footprint with a horizontal 4-pad layout. It presents 120 Ohms of common-mode impedance at 100 MHz, sized to knock down conducted noise on differential signal pairs without loading the line. Rated for 300 mA continuous current and 50 VDC, with a maximum DC resistance of 450 mOhm — the DCR sets the IR drop and self-heating at full load, so the 300 mA ceiling is the practical limit before the temperature rise eats into the 85°C ambient headroom.
Obsolete — sourcing through surplus and last-time-buy channels
TDK has marked the ACM2012E-121-2P-T01 as obsolete.