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Selecting PSU to supply the chosen hardware
| Item | Value |
|---|---|
| Guideline Number | 13 |
| Guideline Responsible (Name, Affiliation) | Timoteo García Bertoa, Sundance |
| Guideline Reviewer (Name, Affiliation) | Igor Tchouchenkov, Fraunhofer |
| Guideline Audience (Category) | HW designers, System architect |
| Guideline Expertise (Category) | TBD |
| Guideline Keywords (Category) | Power, PSU, voltage, load, hardware |
The user should choose the appropriate PSU when testing the corresponding application on the hardware, and appropriately wire it to the low-powered board. PC PSUs are not always providing the correct voltages, as there might be a voltage drop at the wiring, and voltage levels might not be true values at the load. This can mislead users to think the hardware has a problem.
Some of the partners within the Tulipp project have faced the issue of finding "harware not working", when trying their use-case on the Tulipp board. The solution provided in many cases was replacing the PSU for another one that provides the correct voltages, or add a complementary load to pull from the PSU enough current. (i.e. connecting a hard disk to one of the SATA connectors of the PSU). PSUs require a minimum load impedance in order to supply the expected output voltage levels. Some PC PSUs are design with secondary transformers, for low power applications where the 5V rail draws small current, but it's not always the case. Also, using a PSU that is thought for a PC motherboard, might not be using the VSENSE rail correctly, to provide true levels at the load, in this case the Tulipp board.
Recommended implementation method of the guideline along with a solid motivation for the recommendation
The user should always have in mind that the Tulipp board expects 12V,5V and 3.3V as input. From the PSU to the power connector onboard, sometimes there is as a voltage loss. As well, the PSU may be providing not enough voltage to the board, requiring more load, or having to be replaced by another PSU. To find this out, the user should measure the voltage onboard, using a multimeter or any other electronic instrument. If the voltage level is not enough, the user should check the output voltage provided by the PSU, and verify that there is no voltage loss at the wiring. This could be solved wiring VSENSE directly to the load. If there is no voltage loss, an additional load could be added, to increase the overall load impedance, ensuring the PSU is working efficiently as specified by the vendor.
The EMC2 has JP8,JP7 as reference for the voltages. Depending on the position, the user can measure 3.3V, 1.8V and 2.5V. 5V can be measured at the power connector. In case of using a PCIe/FMC application, 12V can be measured at the power connector too. If the voltage measured on the 3.3V pin results less than 3.2V, the user should suspect a possible miss functionality of the board, and try to achieve a proper level. In case of voltage loss, VSENSE could be wired to one of the 3.3V points on the Tulipp board. In case of not voltage loss, to discard PSU's efficiency, a hard disk could be connected through SATA, to increase the load impedance.
Some users had this issue in their testing process, and it was solved, as it can be seen in their reports:
Case 1
Case 2
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TULIPP Guideline Wiki