TPS65400 on PYNQ-Z1 board

[kitt]

Hello!

I purchased the PYNQ-Z1 and I am trying to speed up the synthesis circuit, but when I increase the operating frequency, the power is shut-downed and rebooting occurs.

So I want to know about the design of current limits of PYNQ-Z1.

The power supply IC (TPS65400) which is equipped at PYNQ-Z1, is changeable the maximum current value by setting the register by I2C.
Could you tell me the setting value of (D9h) IOUT_MAX (TPS65400 register) at the shipment of PYNQ-Z1.

Thank you!

[JColvin]

Hi @kitt,

I will need to ask about this; I will let you know what I learn.

Thanks,
JColvin

[kitt]

Hi JColvin,

Here's what to learn:

Even if the vivado tool's synthesis results are within the normal range (speed, power), an unexpected shutdown may occur when implemented on the PYNQ-Z1 and may be due to current detection in the PYNQ power supply circuit rather than the FPGA. (I think current detection is intended to protect the PYNQ board from overcurrent, but there is no documentation that mentions in what range it works.)

Thank you!

[elodg]

You are most probably hitting the USB port power limit (you did not specify how you are powering the board). The Arty-Z7 RM applies to the PYNQ-Z1 as well: https://reference.digilentinc.com/programmable-logic/arty-z7/reference-manual#power_supplies.

 

[kitt]

Hi elodg,

Thanks for your comment.

I am using an AC adapter (12V / 3A) because it was expected that the power supply would be limited by USB power supply. For this reason, the power supply to the PYNQ board is sufficient, and I think that the power shortage is occurring on the PYNQ board.

[elodg]

If you are on external power already, then you are hitting most probably the current limit of one of the power supplies. Since it sounds like you are increasing the frequency of the programmable logic, most probably the VCCINT supply (1.0V) is getting limited. Since power consumption is project-dependent, do a power analysis in Vivado with the implemented project. However, only very complex designs should be hitting the 2.6A current limit on the 1.0V rail. Your project might not even meet timing constraints anymore with high logic utilization and high operating frequency. In other words, you might be having functional problems too with your project, apart from the current limit.

[kitt]

Thanks for your reply.

The Vivado report shows that the VCCINT (1.0V) current is 3.156A, which is certainly above 2.6A. However, there is no particular warning or Error in the Power section of the Vivado project summary. (When the timing or power exceeds the specifications, the excess value should be displayed in red and the implementation result should be Error, but even with 3.156A, the synthesis and implementation are completed normally at the Vivado.)

Is the 2.6A limit of VCCINT not a limitation of FPGA but a limitation of power supply IC (TPS65400) of PYNQ-Z1 board? If so, I think it depends on the setting value of address D9h of the power supply IC (TPS65400) and the design of the peripheral circuit. However, the parameter design of the peripheral circuit is not consistent with the explanation in the data sheet of TPS65400, and "2.6A" is only the comment value of the circuit diagram, so I wanted to know the setting value of address D9h.

[elodg]

Current consumption is not limited by the FPGA. Furthermore, thermal dissipation coefficients are board-dependent. Vivado has no way of knowing what the limitations of the board are.

The board was designed with a 2.6 A current limit because that is what it can safely dissipate. All the power components are sized accordingly. You should refer to the board reference manual for power supply limitations: https://reference.digilentinc.com/programmable-logic/arty-z7/reference-manual#power_supplies, not the individual datasheet of the on-board regulator. We do not recommend you changing the current limit in TPS65400RGZ and drawing more current than the designed maximum. It will void your warranty.