Input resistors on 5V-tolerant I/O

[francesco]

Posted on February 25, 2016 at 16:07

Hi,

I'm quite confused about 5V-tolerant input pins of STM32F405. Referring to the manual, the picture ''Basic structure of a five-volt tolerant I/O port bit'' shows diodes that protect the port. In this configuration, are external resistor needed? In my application I connect some 5V logic port (like 74HCT245) directly to this pins. Must I connect them with a current imiting resistors to protect the processor, or the input pins accept 5V without them? Thanks Francesco #stm32f4-5v-tolerant-tolerant-5v

[waclawek.jan]

Posted on February 25, 2016 at 18:01

> I'm quite confused about 5V-tolerant input pins of STM32F405. Referring to the manual, the picture ''Basic structure of a five-volt tolerant I/O port bit'' shows diodes that protect the port.

And do you see where are those diodes connected? Did you read the footnote below that picture (RM0090 rev.11 Fig.25)?VDD_FT is a potential specific to five-volt tolerant I/Os and different from VDD . > In this configuration, are external resistor needed? No, but you must not enable pullup/pulldown on such pin, nor turn it to output. JW

[francesco]

Posted on March 03, 2016 at 14:59

Thank you Jan,

I've seen the note you report. The words ''different from VDD'' didn't help to understand if the diodes are connected to 5V or another voltage, that's why I asked. Thank you for your help. Francesco