Posted on August 27, 2014 at 13:47
#protection
Hello everybody!
On my board, I want to protect ADC and DAC pins for my STM32F407.Theses I/Os are linked to audio connectors JACK 6.35, the user will be able to plug any 6.35 cables on the connectors. I don't want my uC to be damaged if the user did something wrong, for example we can imagine:- Plug a jack supplying a voltage varying between -30V and 30V on the ADC input.- Even worse, plug ajack supplying a voltage varying between -30V and 30V on the DAC output.
Attached, I designed a circuit inspired of what I found on the internet and on this forum, with bidirectional ESD diodes
PESD5V0S1BA
http://www.nxp.com/documents/data_sheet/PESD5V0S1BA_BB_BL.pdfADC INPUT: a divider bridge converts the connector jack +5V to +3.3V for the uC
DAC OUTPUT: an opamp amplifies the uC +3.3V to +5V for the jack
connector
.What do you think about this design? Is my system well protected against bad uses?
Thanks a lot!
Claire
#protection
Posted on August 28, 2014 at 12:57
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.
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 29, 2014 at 11:08
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).
''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).
