I wish to use the tamper pins of iMX7D processor (SNVS_TAMPER[0:9]). Are these brought out on the SODIMM pads? I was not able to find them on the SoM datasheet; hoping against hope that it is defined under another name!
Another small issue that has been nagging me is that on the Iris and Colibri Evaluation board schematics, the ESD protection diodes RCLAMP0504 have the ‘VCC’ pin connected to 5V rail. Shouldn’t it be the VCC_USBn?
Thanks & regards,
Tamper pins are not made available on the Colibri iMX7 module edge connector, as they are non standard Colibri feature. Currently tamper pins are only available with Colibri VFxx modules.
If you connect the ESD protection diode to VCC_USBn; in such case the ESD discharge will possibly flow via USB power switch to 5V, such power flow path is not preferred.
Preferred solution is to provide least resistance path for the ESD to discharge and skip devices in the path.
Let me know, if you have any further query.
Thank you for the info on tamper pins.
Regarding the ESD protection, I was of the opinion that the source of static electricity would be from the connectors (VCC_USBn line) in which case connecting the TVS diode to 5V will let it flow through the power switch. Am I mistaken?
May I ask the reason why you think that the static electricity will be confined to VCC_USBn line?
From my understanding, it is quite difficult to predict that any specific USB pin will carry static charges.
Lets considering male type USB connector, they generally have a outer metal frame which connects to the body of the USB connector on the carrier board. The body of the USB connector on the carrier board is connected to the SHIELD signal to provide a safe discharge path for the the static charges.
The power and signal pins (VCC, USB_P, USB_N and GND) are not easily accessible, unless and until someone wants to intentionally access it.
So the chance that the static charge will remain in the outer body is higher than being at the inner pins.
ESD protection diodes RCLAMP0504 are connected to USB_P/N signal because we want to protect the processor pins from such discharge as they are not tolerant to ESD.
Let me know, if you don’t agree with my arguments. This discussion will also help me get better understanding on this topic.
I worded my question poorly. My question concerns only whether VCC_USBn or +5V is the better connection to the protection diode. The other USB pin connections, I have no qualms about.
I was implying that VCC_USBn being the external (to board) pin, is more likely to be affected by static discharge rather than +5V which is an internal voltage rail. Also in case of system level ESD protection as provided by RCLAMP0504 (IEC 61000-4-2), protection of external pins seems to be of more importance. (https://www.jedec.org/sites/default/files/Industry%20Council_System%20Level%20ESD_ExpandedVersion_January2014_JEDECversionMay2014.pdf Pg 29).
My understanding of this concept is heuristic; which is why I wished to know if there was a reason for connecting it to 5V.
Thank you for the details and the JEDEC reference.
We had a discussion internally regarding this topic and we also feel that protecting the VCC_USB, signal will be also important.
Please refer to the attached schematics snapshot which is one of the possible ways to protect the VCC_USBn signal.
Let me know you opinion on the proposed changes.