MPQ8880AGVE-0000-AEC1 – PMBus VOUT_COMMAND accepted but output voltage does not change

[dariusz.bogdal]

Hello,

I am testing the MPQ8880AGVE-0000-AEC1 using an Arduino Uno R4 Minima as I²C master.

Current setup:

Device powered and working correctly

Output voltage stable at ~5.0 V

PMBus address: 0x60

Internal feedback divider mode (default configuration)

What works:

Device responds to I²C (ACK OK)

VOUT_COMMAND (0x21) write returns success (no error)

CLEAR_FAULTS (0x03) also works

Problem:

Changing VOUT_COMMAND (for example from 0x341 → 0x226 for ~3.3 V) does not change output voltage

VOUT remains ~5.0 V

I also see unstable behavior when doing multiple transactions (sometimes NACK or bus error)

Additional notes:

I tested single write per reset (to avoid bus issues)

Same result: command accepted, no change on output

I cannot reliably read registers (read operations fail on my setup)

Questions:

Is there any condition required before VOUT_COMMAND takes effect (for example specific mode, register, or sequence)?

Can this MTP configuration (0000) block dynamic VOUT changes via PMBus?

Should VOUT change immediately after writing VOUT_COMMAND in internal feedback mode?

Any guidance would be helpful.

Thank you.

[allison.FAE]

Hi,

Thank you for posting on the MPS Technical Forum.

To answer your questions:

Is there any condition required before VOUT_COMMAND takes effect (for example specific mode, register, or sequence)? No there should not be a specific sequence for a change to take effect, but you may need to save changes to non-volatile memory and power cycle the part.

Can this MTP configuration (0000) block dynamic VOUT changes via PMBus? The MTP configuration is just a preset config. You should be able to make changes freely.

Should VOUT change immediately after writing VOUT_COMMAND in internal feedback mode? You should see changes soon after writing, but, again, may need to power cycle the part.

What do you have MFR_VOUT_CTRL set to? This register sets the internal resistor divider ratio.

The other thing I would also suggest is using the MPS Virtual Bench Pro GUI to help troubleshoot.

Thanks,

Allison