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2389514_en-US
2389514_en-US
I am using 33FS4500 and currently applying the VAUX supply as tracker to act as an external sensor supply. The use case includes short to battery level (32/40V) in error cases.
The 33FS* data sheet states max. 40V for all pins the of chip itself, but does not state the consequences for the external pnp transistor in case of an overvoltage and whether there is a reverse current protection between VAUX and the Buck.
- Is external sensor supply an intended use case of VAUX?
- do I need an extra protection for VAUX?
and if - how does the circuit look like?
a first idea might be a schottky diode between transistor and VAUX (and its feedback).
Dear HajoV,
using VAUX as an external/off-board sensor supply is an intended use case of the FS4500. VAUX can also operate in tracking mode to follow VCCA for ratiometric sensor applications.
For a potential short-to-battery condition (32 V to 40 V), the FS4500 documentation specifies that the VAUX-related pins are rated up to 40 V absolute maximum and explicitly mentions that VAUX is suitable for off-board supplies. It is also recommended to use an output capacitor rated above 40 V.
We could not find any statement in the datasheet, Safety Manual, or FAQ that confirms internal reverse-current protection between VAUX and the Buck/VPRE regulator. Therefore, for robust automotive designs, we recommend considering external protection, such as a Schottky blocking diode and/or a TVS clamp, to prevent back-feeding and improve robustness against fault conditions and transients.
With Best Regards,
Jozef
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