[AD2: V+ Supply Output and Back-Drive Protection]

Thanks @JColvin and @attila! I didn't realize the hardware design guide for the AD2 was online. It is very thorough and well-written. Thanks for making such useful information available! 

[AD2: V+ Supply Output and Back-Drive Protection]

Hi there! I'm curious about what kind of output protection the Analog Discovery 2's V+ supply output has against back-driving.

I'm using the NXP FRDM-KL25Z MCU board. The P3V3 rail is normally powered (via USB and D11) from a linear regulator (NCP1117ST33T3G) through a protection diode D12:

I have cut the shorting trace on the bottom of J20 so D12 can work. For my testing, I disconnect the USB connection (P5V_SDA) and instead use the AD2 to power the board P3V3 supply rail at 3.3 V and below. However, to update code and debug I need to use the USB connection, so it would be easier to keep it plugged in. I can imagine a scenario where I have the AD2 generating a lower voltage (e.g. 2.0 V) for the P3V3 rail, and I plug in the USB cable. U1 would try to drive the P3V3 rail at 3.3 V, and I don't want to damage the AD2.  I can also imagine a scenario where the shorting trace on J20 hasn't been cut, or a shorting jumper has been placed on the J20 header.

Is the AD2 V+ supply output likely to be damaged if a slightly higher voltage is applied in this way with this circuit?

Thanks,

Alex

 

 

[AD2: Switching Digital Inputs Induce Noise on Analog Inputs]

Thanks, @JColvin. It is good to see additional options, though it's too bad that the adapter isn't compatible without some hacking. A custom adapter PCB would be easy enough to make, but the connectors could blow the budget.    (...Once again I am stricken by the Curse of the Engineer: the more ways you know how to solve a problem, the easier it is to get distracted or lost in the details.)   

[AD2: Switching Digital Inputs Induce Noise on Analog Inputs]

Thanks, that helps quite a bit!

• Baseline (+/- analog inputs twisted together): 300 mV p-p noise
• Add 1k resistor in series with digital output: 60 mV
• Twist ground wire (grounded at both ends) around digital signal lead: 25 mV  

And now to figure out the most feasible way to procure 154 such wiring harness modifications/adaptors for 154 students by August 22 🤔. 

[AD2: Switching Digital Inputs Induce Noise on Analog Inputs]

What circuit methods do you recommend for keeping digital input signal transitions from showing up on the analog inputs? 

I'm using the AD2 as a mixed-signal scope to view low-amplitude differential analog signals and twiddle/debug GPIO bits from an MCU (48 MHz). I'm using the flywire harness (connected to a custom PCB mounted on an NXP FRDM-KL25Z MCU eval. board). The analog signals are picking up the transitions on the digital input signals and ringing at ~40 MHz. Adding a series resistor (e.g. 1k) reduces the noise about 5x, and capacitor (e.g. 10 nF) does by about another 2x, though I haven't looked at the impact on signal timing perceived by the AD2. 

Before I spend too much time reading up on snubber networks and RC filters I figured I'd ask if your other customers have run into this and what the common solutions are.    

Thanks for any help!

Alex