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LM53635-Q1: LM53635 input protection

Part Number: LM53635-Q1

Hi all
We are using the LM53635 SMPS for an automotive design. The device supports up to 36V input and tolerates 42V spikes. From previous experience, we think some additional input protection is needed to ensure that the device is not exposed to spikes >42V. We would like to be able to support up to the allowed 36V as input voltage.


Previously, we have used a TVS in combination with a resettable fuse (PPTC) for a lower power design. When the TVS clamped, the PPTC cut power to the device - such that the TVS would not overheat.


We find it difficult to find a TVS which operates at 36V and clamps at 42V. If we select a 42V clamp threshold TVS, the operating voltage will be ~30V (wasting 6V on the input). At the same time, it is difficult to find PPTCs which operates at 2.5/3.5A and breaks before the TVS overheats (they typically require >10A for ~15s).


As the LM53635 (and similar) seems to be specifically designed for automotive applications, we hope that some of you have experience with the required level of input protection needed and how such a protection can be implemented. The design is very space constrained and sensitive to additional BOM cost.


The device is to be used for 12V, 24V and above applications (hopefully up to 36V).


We appreciate any suggestions you can provide.

Thanks

Br

Christian