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PMBus command READ_VIN sometimes violates timing requirements

Other Parts Discussed in Thread: UCD9248

Hi,

I have a design with two UCD9248 controllers, where a CPU monitors all voltages, currents and temperaturs by regularly polling the UCD9248 controllers over PMBus. The problem is that the command READ_VIN sometimes fails. When it fails, it is because the UCD9248 clock streches SMBC, violating "Cumulative clock low slave extend time" t(LOW:SEXT). The other commands (PMBUS_READ_VOUT, PMBUS_READ_IOUT, PMBUS_READ_IIN, PMBUS_READ_TEMPERATURE_1 and PMBUS_READ_TEMPERATURE_2) never fails, and READ_VIN only fails sometimes

Best regards,
Lukas

  • I'm not aware of any issues with the READ_VIN command and the UCD9248 or that would cause regular clock stretching just for this command.
    Is the issue consistent with only one of the two devices or does it affect both devices?
    What speed are they operating the bus?
    Can they provide a screen capture, maybe broken over several screens of a deep capture, showing the issue?
    Can they provide