How to monitor Zybo Z7 voltage using XADC ?

[Mouj]

Hello Guys,

I hope you're doing well.

 

My question is about monitoring the Zybo-Z7 voltage. While the current can be calculated using the equation from page 17/35 in the "Zybo Z7 Reference manual" with X is the voltage from XADC of VP/VN. I'm strugling to find a way to monitor the board's voltage using the xadc.  

Is it possible ?

 

Thanks a lot.

Best regards,

Mouj

 

 

[JColvin]

Hi @Mouj,

I'm not certain which equation you are referring to since there aren't any equations related to the XADC in the Reference Manual I am looking at, https://digilent.com/reference/programmable-logic/zybo-z7/reference-manual, but I know that the XADC wizard will let you select which voltages you want to enable on the XADC module itself. You can then interact and read the registers through JTAG, DRP, or the PS-XADC interface as described in Section 30 of Xilinx UG585: https://docs.xilinx.com/v/u/en-US/ug585-Zynq-7000-TRM.

You can see the corresponding VCCAUX, VCCPINT, and other measurable voltages that are set on the Zybo Z7 that are measurable by the XADC on page 12 of the Zybo Z7 schematic: https://digilent.com/reference/_media/reference/programmable-logic/zybo-z7/zybo_z7_sch-public.pdf.

Thanks,
JColvin

[Mouj]

Hi @JColvin, Thank you for your reply.

In fact, my final goal is to measure the power consumption of the Zybo (or fpga) in a way that is accurate and better than the vivado power estimator.

In the "Current Monitoring" section of the reference manual, the equation (Figure 1.4.1) is used to obtain the current consumed by the Zybo Z7 using the IMON signal from the TPS25940 which is connected to the dedicated analog input pair on the Zynq-7000 (V_P/V_N) ( See attached image or page 14 of the Zybo Z7 schematic).

Is it possible to use the voltage of the IMON signal (VP/VN of the XADC) and the calculated current to measure the power consumption of the board? Can this be considered a good indicator of power consumption?

 

Thanks a lot !

 

Best regards, 

Mouj

 

Edited May 20, 2022 by Mouj

[JColvin]

Hi @Mouj,

Oh, I understand better what you are referring to now.

Yes, you could determine the power being actively used by the device by calculating the current from the equation you referenced and appropriately multiplying by the 5.0 V. As indicated in the reference manual, it may not be a perfect representation (since it is recommended you take an average of the sampled voltage), and I am uncertain if this value will also account for any operating current used by the TPS25940 (the datasheet for it quotes this value at 200 uA typical, https://www.ti.com/product/TPS25940).

Whether or not the value is a "good indicator" depends on how precise you want the value to be. If all you are wanting is a gut check (lets say +- 0.1 Watts as an estimate to accuracy, I have not calculated the actual number of significant figures), then it should be fine (I'm presuming this is what you are wanting since you asking about measuring the power consumption while the design is running rather than simulating it in advance).

That being said, it could as accurate or more accurate than the Xilinx Power Estimator tool, but again, I do not know this for certain. Actual power usage of course is dependent on the characteristics individual components, so determining the power "live" will at least leave you less unknown variables in terms of precision, but you are also at the mercy of if there is going to be problematic spike or drop in power that you won't be able to correct for it in advance.

Let me know if you have any questions.

Thanks,
JColvin