Protect I/Os DAC and ADC of my STM32F4

Posted on August 28, 2014 at 12:26

Hello ,

The ESD diodes will be able to tolerate (+-30V in this case ) Only for small time.

If Voltage continues for some seconds then it will get damaged.

For ADC input: The current will be limited by R4,it will limit the current ,so ESD diode will remain ok.(Also please take care that Vbr of ESD Diode should be less than the tolerance voltage of MCU,as Vbr will directly appear across MCU pin at the time of breakdown).

But in DAC output:The entire voltage (+-30V)will appear across ESD diode and it will get damaged.Please limit the current in this case.

Thanks & regards,

Balmukund Prasad

Posted on August 28, 2014 at 12:57

Hello!

The ESD diodes will be able to tolerate (+-30V in this case ) Only for small time.

 

If Voltage continues for some seconds then it will get damaged.

So maybe it's not the good solution to put ESD diodes? Maybe the best is to put two schottky diodes like this: http://www.microchip.com/forums/download.axd?file=0;634495 ? But the uC have an ADC internal protection with the two diodes.

But in DAC output:The entire voltage (+-30V)will appear across ESD diode and it will get damaged.Please limit the current in this case.

 

So I have to put a resistor of 100R for example after the ESD diode? Or is it a better idea to put the two schottky diode instead of the ESD diode?

Thanks!

Posted on August 28, 2014 at 16:21

Hello ,

In ADC part,there is no problem(As current will be limited by potential divider resistor).

Only thing is that,please select the Vbr of ESD diode close to the tolerance voltage of MCU.

Internal diode will not be able to tolerate 30V.

In DAC Part:

As output impedance of Op-Amp will be almost zero.

It's difficult to protect without any resistor.

Yes,Please put a resistor after after ESD diode (Selection can be done based on power rating of resistor and Load).

Thanks & Regards,

Balmukund Prasad

Posted on August 29, 2014 at 11:08

''In ADC part,there is no problem(As current will be limited by potential divider resistor). Only thing is that,please select the Vbr of ESD diode close to the tolerance voltage of MCU. Internal diode will not be able to tolerate 30V.''

I think i'm going to put a zener diode 5.1V like this one http://www.nxp.com/documents/data_sheet/PZUXBA_SER.pdf because it's preferable to protect this system against continuous voltage overload, than transient high voltages. Maybe I'm wrong ? I don't know if there is a lot of transient high voltages in regular 6.35 cables...

In DAC Part:

 

As output impedance of Op-Amp will be almost zero. It's difficult to protect without any resistor. Yes,Please put a resistor after after ESD diode (Selection can be done based on power rating of resistor and Load).

I think I also want to put a zener diode instead of the ESD diode. On the picture above the end 100R resistor is to low I think.

If I put a 470R resistor I will be able to protect my system against voltages up to 34V according to my calculation. With a 2W resistor and a 0,32W zener diode.

Note: the purpose of my system is to generate and receive CV/GATE signals (a standard for controlling modular electronic musical instruments, through JACK cables). 

Posted on August 29, 2014 at 13:17

Hello ,

Yes ,Zener is the better option for this purpose.

And 100 ohm resistor is low,470ohm will be better option in case of DAC.

Thanks & Regards,

Balmukund Prasad

Posted on August 29, 2014 at 13:24

Hello ,

Yes ,Zener is the better option for this purpose.

And 100 ohm resistor is low,470ohm will be better option in case of DAC.

Thanks & Regards,

Balmukund Prasad

Posted on August 29, 2014 at 13:54

I have another question about protections:

I use the USB port to supply my board and to communicate with a computer. I have to put ESD protections on USB lines (D+, D-, +5V) or is it not required?