Overvoltage protection on Analog Discovery Studio

[jesmith]

Hi, folks. 

Does the Analog Discovery Studio have overvoltage protection for its digital IO, like the Analog Discovery 2? As far as I can tell, the underlying hardware for the Studio is the same as the AD2, but while the AD2 reference manual details +/- 20V overvoltage protection for digital IO (on pages 31 and 32), the Studio's reference manual states (on page 9):

"Important Note: To prevent damage to the device, care must be taken not to drive input signals to the digital input/output channels over 5V."

This is concerning, especially in the context of education. If true, this means a student could cause damage by inadvertently connecting the fixed 12V rails to the digital IO. 

Any clarification would be helpful. 

Thanks!

[malexander]

@jesmith

The Digital I/O protection of the Analog Discovery Studio is identical to the Analog Discovery 2. The statement is section 5 of the Analog Discovery 2 reference manual is correct and applies to Analog Discovery Studio: "Input and output pins are LVCMOS3V3. Inputs are 5V tolerant. Overvoltage up to ±20V is supported."

[attila]

Hi @malexander

Could you comment on this question?

[jesmith]

@malexander Thanks for your prompt response. I assume this means the "important note" on page 9 for the Studio is overly cautious, then?

Further, is there any aspect of the AD2 reference manual that does NOT apply the Studio? That is, our team is now operating with the assumption that most / all of the technical details for the AD2 apply to the Studio, less the obvious feature differences, since the documentation for the AD2 is more complete. Would appreciate confirmation in evaluating the platform for remote education.

Thanks. 

[malexander]

@jesmith

I'm not sure where you browsing the documentation because I don't see page numbers but if you are talking about the statement that says "Important Note: To prevent damage to the device, care must be taken not to drive input signals to the digital input/output channels over 5V." then yes, it's overly cautious. I think the reason we list "Inputs are 5V tolerant" for the AD2 vs "Overvoltage up to ±20V is supported" is because at 5V the PTCs won't trip. If you apply a 20V input at a high enough duty cycle then the PTCs will trip and not allow any current to flow. In both cases current is going to flow through the clamp diodes to the digital 3.3V supply, resulting in a much lower input impedance than what would be seen by a 3.3V signal.

Off the top of my head the only other differences are:
1. The programmable power supply rails on the Analog Discovery Studio are limited to be between +1V and +5V on the positive supply and -1V and -5V on the negative supply.
2. Analog Disovery 2 with BNC adapter supports AC or DC coupled inputs by using a jumper to bypass the coupling capacitor when DC coupling is desired. All inputs of the Analog Discovery 2 are DC coupled.

[jesmith]

@malexander Thanks for the info! Really appreciated.

A related question: what does protection look like for the Studio's fixed 12V rails? To this point, we haven't been able to find documentation, but are interesting in evaluating robustness. 

[malexander]

@jesmith

All of the fixed supplies (+3.3V, +5.0V, +12.0V, -12.0V) have short circuit protection and current limits. Additionally, they are protected to undervoltage/overvoltage of +/- 16V.