# LTC4020 Inductor Current

I'm playing around with the Demo Circuit 2134A. I've noticed that the top and bottom sense resistors are 2mΩ. Wouldn't this equate to an inductor current of 25A (50mV / 2mΩ)? How does the inductor current relate to the max output current?

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• RSENSEA-B serve to monitor the inductor current.  The LTC4020 uses this information to create the control ramp which sets the converter duty ratios cycle-by-cycle.  Additionally, RESENSEA-B establish an average-inductor-current limit so the average inductor current does not exceed a current corresponding to 50mV/(RSENSEA-B).  Finally, RSENSEA/B serve as a gain element (=RSENSEA-B V/A) in the current-control-loop  system function.

• That makes sense, but I'm curious why the demo board is setup for 25A inductor current when the max output is only 8A.

• Let's see.  The demo board is rated for 8A out, VINMIN=15V, VOUTMAX=28V.  That corresponds to a boost ratio of 1.87, so under those conditions the average inductor current will be 8*1.87=14.9A assuming 100% efficiency, greater than that in reality.  3mΩ resistors would limit average inductor current to 16.7A, and there wouldn't be much headroom for dynamic load changes.  So, 2mΩ seems like a good value.  I can only assume the DC2134A designer engaged in similar thinking.

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• Let's see.  The demo board is rated for 8A out, VINMIN=15V, VOUTMAX=28V.  That corresponds to a boost ratio of 1.87, so under those conditions the average inductor current will be 8*1.87=14.9A assuming 100% efficiency, greater than that in reality.  3mΩ resistors would limit average inductor current to 16.7A, and there wouldn't be much headroom for dynamic load changes.  So, 2mΩ seems like a good value.  I can only assume the DC2134A designer engaged in similar thinking.

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