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New Contributor II
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PWRBTN# : Connect to VSYS or 1.8V?

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The documentation says:

"Every Intel® Edison I/O (with the exception of USB) uses 1.8 V signaling."

However, the Arduino Breakout Board (the big one) schematics show, that PWRBTN# has been tied to VSYS (3.3V).

Additionally as far as I remember intel diego also wrote somewhere that if the PWRBTN# functionality is not being used this Pin should be connected to VSYS since it is active low.

So: Is the documentation wrong here?

Furthermore I want to point out that still very important information is missing within the hard user guide. Please include the following information within the next release:


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Employee
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Hello IntelAnonymous,

The documentation is correct, every I/O uses 1.8V signaling. However it seems that the PWRBTN# input tolerates higher values (VSYS). In older posts I mentioned that the PWRBTN# pin has to be connected to VSYS because I used the schematic as reference. I double checked that the PWRBTN# is tied to VSYS by measuring its voltage value. You can measure its value as well. The Test Point (TP) 17 is the one connected to the PWRBTN# pin. Its voltage should be 4.35V approx. which is the same value as VSYS. The VSYS test point is TP1. These test points are at the back side of the board.

I will pass your suggestion of including the information of the links you pointed to the team in charge of the documentation. Thank you for the feedback.

Regards,

Diego.

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Employee
37 Views

Hello IntelAnonymous,

The documentation is correct, every I/O uses 1.8V signaling. However it seems that the PWRBTN# input tolerates higher values (VSYS). In older posts I mentioned that the PWRBTN# pin has to be connected to VSYS because I used the schematic as reference. I double checked that the PWRBTN# is tied to VSYS by measuring its voltage value. You can measure its value as well. The Test Point (TP) 17 is the one connected to the PWRBTN# pin. Its voltage should be 4.35V approx. which is the same value as VSYS. The VSYS test point is TP1. These test points are at the back side of the board.

I will pass your suggestion of including the information of the links you pointed to the team in charge of the documentation. Thank you for the feedback.

Regards,

Diego.

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Novice
36 Views

Hi DiegoV_Intel,

Can you confirm me that an 0 to 1.8V signaling and not an "0 to VSYS (3.3V on my board) signaling" can be ok to control the pwrbtn# pin? I already have measured this pin and it seems, as you said, there's 4.4V. In a new custom design, I have pulled down with a 10k resistor the pwrbtn# pin by default to prevent boot and this pin is controlled by a FPGA at 1.8V for the boot controlling.

Many thanks in advance!

Regards

Mikael

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Employee
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Hello asknt,

In both expansion boards: Arduino expansion board and Mini-breakout board, the PWRBTN# pin is tied to VSYS with a pull-up resistor, so I can't confirm if a 1.8V signal would have the same effect. I guess the only way to know if it works, would be to try it. Another option I can think of for your custom board is to add a voltage translator for this signal. The following is a 1-bit bidirectional voltage-level translator; you might find it useful for your project: http://www.ti.com/lit/ds/symlink/txs0101.pdf http://www.ti.com/lit/ds/symlink/txs0101.pdf

Regards,

Diego.

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Novice
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Thanks for the answer Diego,

effectively I already see/measure on the breakout & arduino boards that this pin is pulled up to VSYS. I wonder that the datasheet only say all I/Os are at 1.8 logic but PWRBTN# . It's a bit dangerous when designing custom boards, hehe! I will tie this pin to another FPGA bank which is at 3.3V logic with the same pull down.

Regards

Mikael

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