zcu104_v_adj_1.8v_tutorial.md

How to change the FMC voltage rail (V_ADJ/VADJ) on the ZCU104 from 1.2V (default) to 1.8V directly from Linux running on the board

Credits to out to @guilhermegog who figured out how to make this work!

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First, find out where your channel id 2 is (chan_id 2, this is where the PMIC that controls the voltage will be listening):

i2cdetect -l

Example output:

i2c-0   i2c       Cadence I2C at ff020000        I2C adapter
i2c-1   i2c       i2c-0-mux (chan_id 0)          I2C adapter
i2c-2   i2c       i2c-0-mux (chan_id 1)          I2C adapter
i2c-3   i2c       i2c-0-mux (chan_id 2)          I2C adapter  <-- THIS IS THE ONE
...

Select the correct ID, i2c-3 (id 3), in this case, corresponding to chan_id 2.

Then run the following commands, where you replace 3 by the obtained id number:

# Select Page 3 on the PMIC
i2cset -y -f 3 0x44 0x00 0x03

# Set Vout Mode (Linear)
# 0x14 = 000 for linear mode and 10100 for the scale (=-12 in 2s complement)
# and results in a scale of 2**-12. Check the manual for more information.
i2cset -y -f 3 0x44 0x20 0x14

# Set voltage to 1.8V (word write)
# 0x1CCC = 0d7373, 7372/2**12 = 1.80V
i2cset -y -f 3 0x44 0x21 0x1CCD w

When we tested this, our id was i2c-4 therefore our commands had -y 4 instead. If you then measure the output voltage, it should have been correctly set to 1.8V!

Links:

• Post on the Xilinx forums about programming the PMIC via external I2C: https://adaptivesupport.amd.com/s/question/0D52E00006hphaLSAQ/enabling-vadj-on-zcu104?language=en_US
• Infineon IRPS5401 register mapping docs: https://www.infineon.com/assets/row/public/documents/24/57/infineon-dc-dc-pol-irps5401-register-map-additionaltechnicalinformation-en.pdf?fileId=5546d46262b31d2e01632da262953416&utm_source=chatgpt.com#page=19.13