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PMBUS communication problem UCD9125

hjoci21
Prodigy 10 points

Dear Sir / Madam

I use one made ​​by Ericsson dc-dc converter which chip is a ucd9125.

problem: I2C commands send to the chips  trigger a NACK response. This happens I2C read and write commands. I tried changing the I2C frequency;100khz and between 10 khz.,the problem is not solved. Push pull resistor is 2k2.The start sign and the chip addressing +W/R the UCD9125 arrived in 28 pin and the 27 pin CLK arrived too, 31 pin have 3.3 V,but no ACK.I tried general call addressing(0x00)but there is still no ACK.

The PCB cooper foil <10cm.

What's wrong this?

Please help sloving the problem.

Can be possible on chip died  I2C communitation?

Thank you for your recommend!

Best regards Jozsef Hajdu

  • 0
    Prodigy 110 points

    Is that the BMR453 or BMR454 ?

    Anyway, if the problem happens all the time, most likely you try to access the wrong i2c address. Try looping through all valid SMBus addresses (eg i2cdetect with Linux). Also try a higher clock frequency; as far as I can recall, a speed of ~350 kHz worked well for me (better than 100 kHz).

    If the chip communication fails randomly, you most likely have a data/clock timing issue. UCD91xx and UCD92xx have very tight timing from data valid to clock high, and sometimes the time from data valid to clock high is a bit below the minimum of 250 nS. This may cause problems with some i2c controllers.

    Guenter