300 Ω common-mode choke — where it fits on a signal line
The TDK ACM2520-301-2P is a 2-line common-mode filter in the ACM series, delivering 300 Ohms impedance at 100 MHz on a signal pair. The 400 mA current rating and 350 mOhm max DCR mean it sits on a low-power differential line — think USB 2.0, CAN bus, or LVDS — where the common-mode noise couples onto both lines equally and the filter knocks it down without degrading the differential signal. The operating temperature band of -25°C to 85°C suits indoor commercial and industrial environments but not under-hood automotive or extended outdoor exposure.
Obsolete — sourcing through surplus and broker channels
TDK has marked the ACM2520-301-2P as obsolete. For a BOM line that depends on this specific impedance and footprint, the supply path runs through independent distribution — surplus inventory, broker-sourced lots, or end-of-life stock. Any replacement candidate must match the pad layout and the 300 Ω @ 100 MHz impedance target to avoid a board spin.
Provenance check — what to verify on receipt
An obsolete part moving through surplus channels demands a physical authentication step. The laser-etched top marking on the ACM2520-301-2P should match TDK's known font and date-code format for the production period. A decap and X-ray inspection will confirm the ferrite core geometry and winding count match the original TDK die — a common counterfeit tells are a different core colour or a winding that does not fill the bobbin uniformly. Moisture sensitivity is not stated on the record, but a standard 48-hour bake at 60°C before reflow is prudent for any SMD ferrite that has been in uncontrolled storage. The tape-and-reel packaging from surplus lots should be inspected for reel date-code consistency — mixed date codes on the same reel suggest the lot was cherry-picked from multiple sources.