UCD9240: PMBUS FREQUENCY_SWITCH NACK

Andrew Holme

Part Number: UCD9240

I am sending I2C commands to a UCD9240 from an FPGA on the Xilinx SP605 board. I can send CLEAR_FAULTS and PAGE commands OK but when I send FREQUENCY_SWITCH the response is NACK even if I request the default frequency of 500 kHz. I have a sensitive ADC attached to the FMC and I wish to implement a spread spectrum EMI reduction scheme to constantly sweep the frequency up and down by a few kHz. I have tried preceding the FREQUENCY_SWITCH with PAGE 0x00 and PAGE 0xFF. Every I2C command is bracketed with START and STOP. I have tried varying the I2C clock. The I2C driver supports clock stretch.

Thanks in advance,

Andrew.

over 4 years ago

0 Qian Chen over 4 years ago

TI__Mastermind 24075 points

HI Andrew,

It is weekend in US now.

We will look at the problem and reply to you next week.

Thanks

Qian

0 Anne Ngo77 over 4 years ago in reply to Qian Chen

TI__Expert 5470 points

Frequency_Switch can be updated only when power conversion is disable on all the rails => Check the ON_OFF_CONFIG (02h) configuration, then turn the rails off based on ON_OFF_CONFIG. If ON_OFF_CONFIG is configured to "Always" convert, then you will need to temporary change ON_OFF_CONFIG to either using Control Pin or OPERATION command (01h), and then turn rails off, then restore ON_OFF_CONFIG to the original value.

0 Andrew Holme over 4 years ago in reply to Anne Ngo77

Prodigy 140 points

Are you suggesting I turn it off, send a frequency command and turn it back on again very quickly before the rail droops? Do you think that is feasible?

Power management

Power management forum

UCD9240: PMBUS FREQUENCY_SWITCH NACK