ESD diode selection

[IJ_YE]

Hi, I am designing a PCB using STM32G0B1RE to be deployed in automotive environment. I need to add ESD protection on its GPIO and ADC pins. I was going through AN5612: ESD protection of STM32 MCUs and MPUs. (Since any specific STM32 family is/are not mentioned in the doc, I think that it should be applicable to all the families.) Under subsection "3.3.4 Other serial interfaces", for I2C-bus ESD protection, the suggested part no. is USBLC6-4. Its electrical characteristics (see attached image) mentions that its V_BR (min) is 6.1V. 

As per the STM32G0B1RE datasheet, the maximum allowable voltage on any pin is 4.0V to 5.5V (depending on the pin).

As per my understanding, V_BR of the ESD diode should be less than the AMR (Absolute Maximum Rating) of the concerned pin. My doubt is that whether the above mentioned ESD diode would be appropriate or are there some other parameters that are needed to be taken into consideration?
What is the best approach to select the ESD diodes for ADC and GPIO pins (max. 3.3 working voltage)?

[AScha.3]

Hi,

the USBLC6-4  is for use on USB port , usb has 5V + , so its overvoltage protection at 6 V is ok.

The data lines have diodes to gnd and V+ , so they will limit here;

if you want better protection for data lines -> cpu pins, use the USBLC6-4 or something similar, and connect it to gnd and vdd 3v3 , not on usb 5V , so better protection for the cpu pins.

+

>

What is the best approach to select the ESD diodes for ADC and GPIO pins (max. 3.3 working voltage)?

Depends on : what is or could be on the line ?

If you have slow signals, just put a big ceramic cap to gnd there, no more esd problem.

And add fast diodes to gnd and vdd , for more safety.

The problem is : if you want fast signals pass, as on USB , you cannot put big diodes there,

as their capacity is also big and not suited for fast signals.

So its always some kind of compromise .

see at mouser...ymmv.

https://www.mouser.de/c/circuit-protection/esd-protection-diodes-tvs-diodes/?working%20voltage=3.3%20V

[IJ_YE]

Hi @AScha.3 
In the above-mentioned doc, ST has suggested this diode for I2C lines, which are usually on 3.3V. So, in this case what is the significance of V_BR (Breakdown voltage between VBUS and GND) = 6V (min.)? Also, the clamping voltage for this diode is 12V, which, as per my understanding, means that in case of very high voltage ESD situation, will clamp the line voltage to 12V, but this is too high for the STM pins to sustain. So, how come this diode would be appropriate to be sued with STM32 pins?

[AScha.3]

>So, how come this diode would be appropriate to be sued with STM32 pins?

use the USBLC6-4 or something similar, and connect it to gnd and vdd 3v3 , not on usb 5V , so better protection for the cpu pins.

Vbus here -> Vdd , 3v3 .

The zener only useful for USB , at 5V .