Author Topic: Power sequencing - chip powered via it's IO  (Read 607 times)

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Offline Pat PendingTopic starter

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Power sequencing - chip powered via it's IO
« on: April 13, 2019, 06:57:27 pm »
Hi

I have two connected chips (master/slave), both powered at 3v3.
When power is removed from the slave it's supply rail shows 1.9V - the outputs from the master back feed power into the slave.

The difference is 1.4V. One diode should be the protection diode on the IO and would account for 0.7V but I can't explain where the other diode drop (i assume) would be.

I Googled but still looking for a good explanation.

Thanks
 

Offline Doctorandus_P

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Re: Power sequencing - chip powered via it's IO
« Reply #1 on: April 13, 2019, 07:33:27 pm »
Some 3V3 microcontrollers have an internal voltage regulator and work with a lower core voltage.
There may also be some modified internal structures to make pins compatible with 5V logic.


I wouls also not assume it's only ESD diodes, nor that the voltage drop over an ESD diode is 600mV.
 


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