AD2: V+ Supply Output and Back-Drive Protection

[AlexanderGDean]

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

 

 

[JColvin]

Hi @AlexanderGDean,

I am not certain of the exact answer (maybe Attila will be able to offer some more details once it is regular working hours in his European timezone).

I know that based on Section 6.3 of the Hardware Design Guide, https://wiki.digilent.com/reference/test-and-measurement/analog-discovery-2/hardware-design-guide#power_supplies_and_control, that the particular IC in question for the User Supplies has low voltage drop reverse supply protection as well as analog undervoltage and overvoltage protection though I'm not readily able to determine the details of what those two line items mean from the related sections and equations of the guide, but perhaps you might find some insight from the listed information.

Thanks,
JColvin

[attila]

Hi @AlexanderGDean

The supplies should be protected, see the schematic:
https://digilent.com/reference/test-and-measurement/analog-discovery-2/hardware-design-guide

As usual, make sure the devices use the same ground level.

The AWG outputs are sensitive for back powering, specially when these are unpowered, before software connection.

[AlexanderGDean]

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!