80 Ω at 100 MHz — common-mode attenuation on a differential pair
The TDK ACM3225-800-2P-T is a 2-line signal-line common-mode filter from the ACM series, packaged in a 1210 (3225 Metric) footprint with 4 leads for surface-mount assembly. Its headline rating is 80 Ohms impedance at 100 MHz — the frequency where conducted EMI from switching regulators and digital clocks typically couples onto differential signal pairs. At that impedance, the filter presents a high series impedance to common-mode currents while leaving the differential signal largely unaffected, so it cleans up the line without degrading the data eye.
400 mA current ceiling and 150 mOhm DCR — the insertion-loss trade-off
Rated for 400 mA continuous DC and 20 VDC maximum, with a maximum DC resistance of 150 mOhm. The DCR times the square of the load current gives the self-heating: at 400 mA, I²R dissipation is 24 mW, negligible for the 1210 body, but the voltage drop across the filter at full current is 60 mV — a consideration if the downstream rail has tight tolerance. The 20 VDC rating limits it to low-voltage supply rails and signal lines; it is not a power-line filter.
Obsolete — sourcing through independent channels
TDK lists the ACM3225-800-2P-T as obsolete. No pin-compatible direct replacement from TDK is documented, so a board-spin or a parametric search for a 1210 2-line common-mode filter with matching impedance and current rating is the migration path for new designs.
Temperature grade and board-fit
Operating temperature range is -25°C to 85°C — a commercial/industrial band that covers most indoor equipment and telecom enclosures but not under-hood automotive or extended industrial ambient above 85°C. The 1210 (3225 Metric) 4-lead package is a standard SMD footprint; reflow profile follows the common JEDEC J-STD-020 for a component of this size.