I would like to ask about Vout Enable Output Pin state when LTC2977 is not powered up. Does it behave as pull-down (weak or strong) or is simply floating. The output circuit schematics will be very helpful.
The VOUT_EN pin is high impedance when the chip is not powered. The pin is an open drain Nch whose gate is internally driven by logic powered from VDD33. At powerup, as VDD33 voltage rises, the internal gate follows VDD33. The Nch begins to turns on when VDD33 is ~0.7V, and weakly pulls the pin to GND. The Nch exhibits a lower impedance as VDD33 voltage continues to rise (Vgs increases), and is fully turned on above 1V. See the graph labeled VOUT_EN Output Voltage vs VDD33 on page 12 of the LTC2977 datasheet. This behavior occurs independent of configuration settings. This way you can be assured that the 2977 keeps its managed channels off until the chip finishes initializing (RAM is loaded from NVM) at which point the sequencer begins to apply TON_DELAYs. This is the tINIT time which is nominally 30ms.
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