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Open ReX : Board Schematic Doubts

Abhi P Choksi , 08-14-2019, 12:32 AM
I am learning schematic of Open Rex board by my self.

I will post my doubts over here in this thread.

#Doubt 1: Why VDDHIGH_IN and VDD_SNVS_IN are shorted?
As per part datasheet, it stated that we may short it together.
But as per Hardware design Guide its stated to Supply VDD_SNVS_IN from VSNVS of PF0100.
Please clarify me on this.

robertferanec , 08-16-2019, 08:34 AM
Depends on your implementation. If I remember right, it depends on the power options what you would like to use - if you are planning to use some power saving modes or batteries you may want to connect it differently as if you are going for more simple variant (?). PF0100 probably directly supports SNVS output, so you can connect it there - however if you do not use PF0100, to make it more simple you may connect it together (?)

But it was long time when I read the datasheets, so I do not remember exactly.
Abhi P Choksi , 08-18-2019, 10:14 PM
I appreciate your answer.I totally got it.Thanks.
Abhi P Choksi , 08-18-2019, 10:18 PM

I want to understand how this circuit would work for USB Switching.

I have doubt on topology used with P-MOSFET. Will this circuit work?

robertferanec , 08-19-2019, 02:42 AM
@Abhi P Choksi The circuit works as described in the design notes on the schematic page. Please, what are your doubts about?
Abhi P Choksi , 08-19-2019, 04:48 AM
@robertferanec ,
​As per the Electronics, Vgs must be less than Vth to make P-Channel MOSFET switch ON.
I could not able to satisfy this above rule when Jumper link is connected or MOSFET gates are connected to the GND.
Please clarify me in these terms.

#Also, Why to use two P-Channel MOSFETs in this type of "Series configuration"?. Any advantages of this configuration?
Actually, it's possible to switch USB power On/Off using single P-Channel MOSFET.
robertferanec , 08-20-2019, 08:42 AM
Vgs must be less than Vth to make P-Channel MOSFET switch ON.
This may help: https://www.falstad.com/circuit/e-pmosfet.html

Basically, if SG is 0V, transistor is OFF, if SG is higher than threshold transistor is ON.

source: https://www.electronics-tutorials.ws...or/tran_7.html

Why to use two P-Channel MOSFETs in this type of "Series configuration"?
- depends if the board is configured as Host or Device. If configured as host, it needs to be able to send power out, if configured as device it has to be able to be powered from USB. If you only use 1 transistor, there is usually diode inside and you will not be able fully control (completely ON / OFF) the flow between Board Power and OTG power.
Abhi P Choksi , 08-22-2019, 11:29 PM
#Doubt 3 : What reference you took for SATA Interface in OPEN REX Board.
robertferanec , 08-23-2019, 07:10 AM
Please, could you be more specific? I am not sure what you mean by "reference".
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