I'd like to know the purpose and effect of the resister and bead located on the drain of bottom FET, like R17-23, and L3-10 at "LM3433 10A to 40A LED Driver Evaluation Board".
I believe that this can reduce switching noise, however I would like to have your comments in case.
The bead/resistor combination is to reduce switching noise, mainly the noise caused by the reverse recovery charge of the high side FETs when the low side FETs turn on. However, it isn't simply a matter of noise. This is a high current circuit with substantial FETs, the reverse recovery of the high side FETs can cause a substantial spike well below -VEE that can damage the HS pin of the LM3433. The beads reduce the spike to protect the IC and the resistors are there to dampen any potential resonance between the beads and the parasitic capacitances of the FETs.
Hi Clinton Jensen-san,
Thank you for your reply.
I understood that the bead/resistor it to reduce switching noise and also protect the HS pin from substantial spike noise.
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