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LM25148-Q1: LM25148 Rsense value calculation with the tool

Part Number: LM25148-Q1
Other Parts Discussed in Thread: LM25148

Tool/software:

Hi team,

Customer RD is facing the wrong calculation result on LM25148. Per actually test on system, they found it should be using minimum value to calculate the required Rsense to prevent the OCP error triggering. Please check and consider to modify the design tool we publish online. Thanks. 

FYI

Regards,

Alex

  • Hi Alex,

    Thanks for the feedback. I will take it back to the team.

    The calculator represents a typical device based on typical rated values for the necessary specifications.

    It is always good practice to calculate the maximum and minimum possible component values based on variation in spec listed in the datasheet. The calculator tool is always a good starting point, but the customer needs to evaluate and validate the design on their own to identify potential discrepancies such as the one your customer has seen.

    Best regards,

    Ridge

  • Hi Alex,

    The calculator derives the shunt value using the typical current limit threshold. 22.3A current limit is too close to the 20A full-load rating. We generally recommend setting it at 130-140% to deal with load-on transients when the inductor current overshoots.

    Note also that shunt accuracy has an influence, especially given the two components in parallel here. I recommend using one 2mΩ shunt. Also, ESL plays a factor, as it creates a squarewave voltage on the shunt from the divided down SW-node voltage (this is more a concern at higher input voltages, however). Lastly, check that the current sense traces to the controller are routed as a diff pair away from gate drive and switch-node high dv/dt noise sources.

    Regards,

    Tim