What's maximum allowed current on pmod of zedboard?

[Leon18]

I am using PMOD (differential JD1) for I2C communication (SDA, SCL). I only have one board so I don't want to accidently damage my zed board. In order to decide the value of pull-up resistors, I have to know the maximum allowed current for PMOD. Folks said normally pull-up resistors should be around 4.7k ohm and smaller resistors are better. (https://learn.sparkfun.com/tutorials/i2c/all).

Edited November 6, 2023 by Leon18

[zygot]

According to the PMOD Standard ( such as it is, and it's quite dated ):
The amount of current that a peripheral module is allowed to draw from the host is not specified, but it is assumed that the Pmod will not draw more than approximately 100mA.
The document can be found here: https://digilent.com/reference/pmod/specification

Different boards with a "PMOD" header support varying levels of 3.3V current draw. It depends on how many PMODs are being used, and the specific board power supply design for any given board. There are plenty of boards, FPGA based or not, AMD or Intel or other, that have adopted the PMOD form factor, but not necessarily the 3.3V/GND pinout.

For the schematic shown, what's important is to ensure that the resistor values for open-collector ( open-drain ) or signals that can be Hi-Z, the pull-up resistors are consistent with the standard. This is complicated by the fact that there are a number of knock-offs of the original I2C interface standard.

Digilent has never been organized enough to produce anything that might be appropriate to be called a "standard". That hasn't prevented it from becoming ubiquitous, unfortunately. Edited November 6, 2023 by zygot

[JColvin]

Hi @Leon18,

As @zygot indicated, there is no firm rule on the amount of current a Pmod is allowed to draw from a host (outside of the assumed not needing to draw more than 100 mA).

Looking at Table 20 within section 2.11 of the Zedboard Avnet User Guide (available here: https://digilent.com/reference/programmable-logic/zedboard/start#documentation), they have a generic estimate of 3 A being allocated to the 5 Pmod ports and the FMC connector. Discounting 2 A to the FMC connector (as that is based on whatever you have VADJ set to), this supposedly leaves around an amp between the 5 ports.

Of course, there isn't anything physically stopping the end user from attempting to draw more current from any of the voltage rails, nor will that Table 20 perfectly reflect whatever design you have implemented.

Let me know if you have any questions.

Thanks,
JColvin