smd common mode chokes operating principle interferences propagating via supply or signal lines can be suppressed by placing a high impedance in series. this can be provided by a ferrite inductor. however, saturation by the supply current can be a problem. remedies are a low permeability material or a gapped / open magnetic circuit. the disadvantage is the large number of turns required to achieve the required inductance, leading to high copper losses. with standard suppression methods in a signal path, the wanted signal is often suppressed along with the interference, and in many modern applications (edp for instance) this leads to unacceptable loss of signal. this can be overcome with current compensation , based on the fact that supply or signal currents in both lines are opposite and have equal magnitude. in philips new interference-suppression beads, a pair of conductors within a single soft-ferrite block are connected along their lengths by an air gap. common-mode signals - interference signals passing in the same direction along the input and output channels of a device (a ic for instance) - serve to reinforce the magnetic flux around both conductor, and are therefore attenuated. in contrast, the wanted signal passing along the input and output channels serves to cancel the flux around the conductors and therefore passes unattenuated. these common mode chokes are available in 2 sizes in 4s2 material with 2 different winding configurations. in combination with appropriate tracks on the pcb the products can also serve as . multi-turn choke transformer the main application areas for the smd common mode choke can be found in e.g. electronic data processing telecommunication consumer electronics domestic appliances smd common mode chokes philips components magnetic products november 1994 14
features resistant to mechanical shocks and pressure high resistivity material low tolerances of mechanical dimensions enable automatic mounting flat sides to improve handling by automatic placement machines low leakage inductance suitable for different functions, depending on pcb connections applications emi suppression supply line filtering data line filtering type description e.g. cms2-5.6/3/4.8-4s2 (1) (2) (3)(4)(5) (6) (1)product type (cms= common mode surface mountable choke) (2)number of strips (3)width nominal (in mm) (4)height maximum including wire (in mm) (5)length nominal including wire (in mm) (6)material grade packaging and ordering codes (11 nc) 4330 030 36881 (type number cms2-5.6/3/4.8-4s2) 4330 030 36911 (type number cms4-11/3/4.8-4s2) the first 11 digits of the 12 nc are sufficient to order the desired smd bead. smd common mode chokes are delivered taped and reeled, ready for use on automatic mounting machines. packaging is according to iec 286-a and eia 481-a. packing quantity: 2400 pcs./reel smd common mode chokes magnetic products philips components 15 november 1994
4.75 0.3 + _ 1.33 0.2 + _ 1.27 0.07 + _ >1.1 >1.2 5.6 0.2 0.2 + _ max 3.04 4.75 0.3 + _ 1.33 0.2 + _ 1.27 0.07 + _ >1.1 >1.2 10.8 0.3 0.2 + _ max 3.04 electrical characteristics type number remark impedance ( w ) at frequency mass 30 mhz 100 mhz 300 mhz (g) cms2-5.6/3/4.8-4s2 23 35 50 ? 0.3 cms4-11/3/4.8-4s2 inner channel 13 23 42 ? 0.6 outer channel 16 30 50 *nominal impedance values measured at 25 o c with hp4191a impedance analyzer. minimum values may be up to 20% lower! smd common mode chokes fig.1 smd common mode choke with two conductors (cms2-5.6/3/4.8) fig.2 smd common mode choke with four conductors (cms4-11/3/4.8) philips components magnetic products november 1994 16
recommended solder lands 6.4 2.8 1.8 1.9 2.5 6.4 2.8 1.8 1.9 2.5 0.8 smd common mode chokes 6.4 2.8 1.8 1.9 2.5 0.8 6.4 2.8 1.8 1.9 2.5 fig.3a solder lands for reflow soldering of cms2-5.6/3/4.8 fig.3b solder lands for wave soldering of cms2-5.6/3/4.8 fig.4a solder lands for reflow soldering of cms4-11/3/4.8 fig.4b solder lands for wave soldering of cms4-11/3/4.8 magnetic products philips components 17 november 1994
typical impedance curves 200 0 1 mww004 10 100 1000 40 80 120 160 f (mhz) 1 turn z ( w) 2 turns cms2-5.6/3/4.8-4s2 200 0 1 mww005 10 100 1000 40 80 120 160 f (mhz) 1 turn z ( w) 2 turns inner channel outer channel cms4-11/3/4.8-4s2 smd common mode chokes fig.5 impedance as a function of frequency for cms2-5.6/3/4.8 (1 and 2 turns). fig.6 impedance as a function of frequency for cms4-11/3/4.8 (1 and 2 turns). philips components magnetic products november 1994 18
smd beads in action magnetic products philips components 19 november 1994
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