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LTC4633 Issue at start up

Question asked by Lorenzo_m on Jul 5, 2018


we have some problems with this chip: it works properly when it is supplied with a 28V but when we powered it with 9-10V, it doesn't work as expected: before starting it waits for 9 seconds and then start to charge the mosftet creating a ramp in the output. I attached some pictures about the oscilloscope input and output at 10V. The circuit used is attached in the schematic, except for the mosfet that is a little bit different (in real circuit IXFB210N30P3) which has a typical VTH of 2,5V. The resistances values are extrapoleted from the evualation board DC2150A which is expected to work from 9V. 

Thanks in advance for any help.

Best Regards