LM5176-Q1: Automotive power design

Hi Kai,

thank you for using the E2E forum.

There are a few things to consider.

Typically I would suggest designing the powertrain (inductors, capacitors) for the typical operating conditions. For this design 7V should be considered the minimum input voltage for the normal operating condition. This will help ensure the saturation current is selected properly. For the nominal range is 7V-18V. Designing these components for this range will help boost the efficiency in the normal operating range. Typically the boost mode operation is going to dictate the current sense resistor and inductor value. To help push the RHP zero of boost mode to higher frequencies I like to set the ripple ratio at 40% to 60% to ensure the inductance value is fairly small.

The MOSFETs and the compensation should take into account the total operating range, 7V to 36V. Typically the compensation should be designed for the worst case boost condition as the RHP zero of the boost needs to be taken into consideration. Then just check it at 36V (buck mode) to make sure the response is reasonable. The MOSFETs should obviously be rated to handle the maximum input voltage. Typically for 36V VIN 40V FETs can be used depending on how much margin the customer wants. But pushing for 40V MOSFETs will proved the best efficiency and will have the most selection available for logic level FETs.

 Best regards,

 Stefan