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TPS40400 / defaul value of register

K.Yaita
Guru 29720 points


Hi,

I'd like to ask about default value of VOUT_OV_FAULT_LIMIT(40h) and VOUT_UV_FAULT_LIMIT(44h) register.

In datasheet P.32, there is description that default value of VOUT_OV_FAULT_LIMIT is 112%(default) and "0000_0101_0000_1000(dec:1288)" .

 

I think 112% is inconsistent with this code.

The code "0000_0101_0110_0000(dec:1376)" seems to be converted to 112%. 

Which is correct value of default? (112% or "0000_0101_0000_1000(dec:1288)")

Regards,

Yaita

  • 0
    Guru 29720 points

    Hi,

    I think  the default code "0000_0101_0000_1000(dec:1288)" is calculated to 104.82%, so it seems mismached.

    Could you follow me please?

    Regards,

    Yaita

  • 0 in reply to K.Yaita
    Guru 29720 points

    Could you follow me please?

    I have to explain to my customer about this.

    Regards,

    Yaita

  • 0 in reply to K.Yaita
    TI__Guru**** 191445 points

    I looked at this.  It does not make any sense to me either.  Tomorrow I will see if I can find out who is responsible for it.  In my opinion that datasheet is unusable.  Please do not be in any hurry for an answer..it may take some time.

  • 0 in reply to JohnTucker
    Guru 29720 points

    Hi, John-san

    Thank you for your reply.

    OK. I will wait for the answer.

    Regards,

    Yaita

  • 0 in reply to JohnTucker
    TI__Guru**** 191445 points

    I think I have this figured out.  the value is in V x 2^-10.  So 0508H = 1288 corresponds to a trip point of 1.288 V.  It will round to the nearest percent of the 4 fixed values.  It assumes that you have properly programmed the correct output voltage and set the feedback resistors, VOUT_MODE, etc all correctly as well.  This is a really complicated device.  I suggest that you read and understand the PMBus 1.1 specification thoroughly.

    So you have to set the OV trip voltage in absolute voltage in between the four preset percentage levels.

    Let me know if you have further questions.

  • 0 in reply to JohnTucker
    Guru 29720 points

    John-san, 

    Is it possible to change the value of the register even if customer doesn't access(write) before?

    My customer read the value of VOUT_OV_FAULT_LIMIT(40H), but the read value isn't 0508H in spite of he didn't access the register before. (He said the actual read value is 0560H.)

    I can't catch the meaning of "Default Value(0508H)" in datasheet P.33.

    Regards,

    Yaita

  • 0 in reply to K.Yaita
    TI__Guru**** 191445 points

    The datasheet does not make this clear.  The way I read it, the default values are stored in the non-volatile registers.  What you may read in the "ordinary registers may  be random on power up.  You have to issue the command to restore the default values,

    RESTORE_DEFAULT_ALL
    (12h)
    The datasheet does not really go into the general operation. I think it is assumed that you have some idea of the protocol if you intend to use the device.  I have to tell you that I have never used this personally.  My comments are just based on reading.  I may try to get an EVM to set up and experiment with.
  • 0 in reply to JohnTucker
    TI__Expert 4350 points

    Yaita-san,

    Your understanding of the hex code is correct. It is the datasheet that has an error. The default setting for VOUT_OV_FAULT_LIMIT (40h) is indeed 112%, which is 0x560. The datasheet needs to be corrected.

    As for the defaults, and volatile memory, and non-volatile memory (NVM), all of the values in NVM are the power-up defaults. That is, when the device is powered-up, the device uses whatever is programmed in NVM. Once the device is running, you can change the volatile memory settings one by one by updating their values (in the TI Fusion GUI, this is done with the “Write to Hardware” button after a change in entered in the desired parameter), and those settings will take effect (with some exceptions) as soon as they are updated (again, in the TI Fusion GUI, this is done with the “Write to Hardware” button). However, those changes will be lost when input power is cycled, unless the changes are committed to NVM.

    In order to commit changes to NVM, you must issue either the STORE_DEFAULT_ALL or STORE_DEFAULT_CODE command. In the TI Fusion GUI, this is done with the “Store Config to NVM” button. Once changes are committed to NVM, they become the new power-up defaults.

    MC.

  • 0 in reply to Martin Cardella
    Guru 29720 points

    Martin-san, John-san

    Thank you for your support! I can understand.

    It seems the same error about VOUT_UV_FAULT_LIMIT(44h). Blue  is correct and red isn't.

    I am glad if you verify that.

    Regards,

    Yaita