BLM21SN300SN1D

• 4 M Ohm DC Resistance for Negligible Supply-Path Voltage Drop
• 8.5 A RMS and Maximum Current Rating
• Multilayer Ferrite Core construction, Single Line
• Characterised at a 100 MHz Test Frequency
• 0805 Imperial / 2012 Metric case, 2.01 Mm X 1.24 Mm X 1.04 Mm
• -55C to +125C Operating range, RoHS Compliant

The BLM21SN300SN1D from Murata is a multilayer ferrite bead in the 0805 case size (2012 metric), measuring 2.01 mm x 1.24 mm with a 1.04 mm profile. A ferrite bead presents low resistance at DC and rising impedance at high frequency, so it passes supply or signal current while absorbing and dissipating high-frequency noise rather than reflecting it. This part has a very low 4 m Ohm DC resistance and an 8.5 A RMS current rating, an unusual combination that lets it sit in a high-current supply path with negligible voltage drop. It is characterised at a 100 MHz test frequency, covers a single line, and operates from -55C to +125C. The BLM21SN300SN1D is RoHS compliant.

Ferrite beads with single-digit milliohm DCR and multi-amp current ratings are placed in power rails rather than signal lines: isolating a noisy switching regulator output from sensitive analog, RF or clock circuitry, containing conducted emissions at a module or board boundary to pass EMC testing, and decoupling the supply pins of processors and power amplifiers. Because the DC drop is only a few millivolts even at several amps, the bead can go directly in a main rail without a regulation penalty. The -55C to +125C rating and 0805 size make it a fit for automotive, industrial and telecom power distribution. Buyers are EMC and power-integrity engineers resolving emissions or noise-coupling problems, plus sourcing teams supporting automotive-grade filter BOMs. Note that the impedance value is not present in this catalogue record; confirm the impedance-versus-frequency curve against the Murata datasheet.