Other Parts Discussed in Thread: TPS40210
Hello, it looks like my circuit using a TPS40210 (I'm using the EP version, if that matters) has some issues restarting from temporary power interruptions when a large soft start capacitor is used. I have a very big capacitive load at the converter output, therefore if I use "typical" Css values (1 uF or less) the hiccup overcurrent protection trips and the conversion does not start. I've fixed this by using a bigger soft-start capacitor (10 uF), but with this configuration another problem appears: if I disconnect the input voltage for a short time (let's say less than 1 second), the converter "shuts down" forever until the next power cycle. The output voltage slowly drops to the input voltage, and I don't see any activity on the GDRV pin or the switching node. Instead, for longer power interruptions (let's say 2 seconds or more) the conversion restarts normally: the output voltage ramps up to the final value.
I suspect that the short power interruptions "upset" in some way the soft start and overcurrent stage of the controller (perhaps some sequential logic goes into an invalid state?).At the moment I've fixed this issue by connecting a 10 uF capacitor on the BP pin. I haven't done extensive tests yet, but with this modification the converter seems to start always, independently from the power interruption duration.
My questions are: is this a known issue? Is increasing the Cbp capacitance a suitable/preferred solution to fix it? The datasheet clearly states to use a 1 uF value for Cbp.