in absence of main power, SAM E70 drawing power from UART pins

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Harikrishnan911
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Posted by Harikrishnan911: Sat. Jul 22, 2017 - 07:09 AM
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I noticed that my VCC line is reading 1.5V even in the absence of main power.

Only connection present is TX, RX and GND connection from a silicon labs USB to TTL converter.

Am reading 2.2V approx at pin PA21 from the USB to TTL converter.

GND & PB4 pins are at ground potential.

 

This is the only connection left & the TX & RX pins runs directly to the sam E70 & there are no pullups present.

Then what could be cause of 1.5V that I am reading at the vcc pin?

This topic has a solution.

Silly beans are always silly
:)

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Atmel SMART ARM-based MCUs and MPUs, Atmel Cortex-M MCUs, solved
Last Edited: Sat. Jul 22, 2017 - 09:54 AM
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Kartman
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Posted by Kartman: Sat. Jul 22, 2017 - 07:40 AM
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Most cmos devices have protection diodes. Because your rxd pin is above vcc, these diodes will conduct.

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Harikrishnan911
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Posted by Harikrishnan911: Sat. Jul 22, 2017 - 09:54 AM (Reply to #2)
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Oh, that makes sense.

You are right. Diode losses adds up to 0.7V.

yes

Silly beans are always silly
:)

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