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Synchronous rectifier driver needs added inductor.

cupoftea

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Hi,
Why does the LTC3901 datasheet not mention the need for the inductor L6 as shown attached. Without this inductor , the synch rect driver will not work properly.
LTspice and jpeg as attached.

(BTW , the bit in the dotted line monitors the output current, and disables the synch rects in light load...another necessary feature, again not mentioned in the datasheet....there are large overvoltage spikes on the synch rect FETs when in light load if the synch rect FETs are not disabled in light load)

LTC3901
LTC3723
 

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  • PowerPack_FBCD_shutoff_LTC3901_A.zip
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  • Synchronous rectifier driver.jpg
    Synchronous rectifier driver.jpg
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The inductor is relied upon, but is likely to come from the transformer leakage, also the FET capacitance is probably modelled more than really is at all voltages. Just makes you wonder when doing these things with planar transformers with super low leakage inductance.
 

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