Resistor configurarion used for VBUS configuracion

[Aldo_Flores_Aguayo]

Hi, I´m reading the following document : "an4879-introduction-to-usb-hardware-and-pcb-guidelines-using-stm32-mcus-stmicroelectronics" to implement USB in my application. 

In section 2.6.1 Simple Resistor Divider it says "This solution works well as long as GPIO maximum operating conditions are >= VDD+ 3.6 V" this must be meet to use the following voltage dividider 

I´m going to use PA9 pin, in the datasheet of my MCU STM32L4P5RGT6 it states this pin is 5V tolerant 

As I understood this pin doesnt meet the condiciton mentioned before because my VDD=3.3V and so GPIO maximum operating condition should be >= VDD+3.6V so we have 3.3+3.6V=6.9V so 5V < 6.9V so I can't use this configuration do I understand this well ? 

 

Should I use this other configuration? 

I´m a bit confused about it hope some one could help me to clarify this. 

 

[TDK]

It'll work.

 

PA9 is a 5V tolerant pin.

So incoming voltage limits are VDD + 4.0 V:

 

Voltage there will never be more than 3.75 V, as long as VBUS respects USB limits (4.75 V to 5.25 V).

 

The issue here is ensuring the voltage on the pin is acceptable when the device is off. This is satisfied.

[FBL]

HI @Aldo_Flores_Aguayo 

PA9 is a five volt-tolerant pin, including an additional function natively dedicated to VBUS sensing.

The absolute maximum ratings table of the datasheet indicates that the five volt-tolerant pin voltage cannot exceed VDD+ 4V.

You can check the schematics of STM32L4P5 Disco board provided as reference:

 

[Aldo_Flores_Aguayo]

Thanks for your replies @FBL @TDK 

Okay, I think I got it, so just one question why in one parte of the"  introduction to USB hardware" it shows the following

 

"five volt-tolerant pin voltage cannot exceed
VDD + 4 V."

 

And then in the MCU datasheet the the following appears with respect to five volt tolerant pins 

 

So it´s VDD+4V or min(VDD) +4V ??

 

Hope you can clarify this, thanks for your time.

 

[TDK]

> There is a notable difference when using VDD+4V or min(VDD)+4V.

Think they're the same. When the chip is not powered, VDD = 0. The datasheet has the details.