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TPS40400 PMBus using.

Sergej Dziuba
Intellectual 265 points
Other Parts Discussed in Thread: TPS40400

Hi!

We are going to use TPS40400 to get adaptive voltage scaling for TMS320C6A8168, but we need to get right power sequence for proper processor operation.

TPS40400 will make 1V AVS and this voltage should start after 3.3V has started. To get right voltage's sequence here must be EN input in TPS40400, but here is only CNTL pin which can behave dependent on programmable parameters in TPS40400.

Question: what is the default behaviour for CNTL pin?

We need that it behaviour would be like EN pin without any commands by PMBus. We don't have any adapters to programm TPS40400 before assembly it on PCB.

Thank you.

Sergej.

  • 0
    TI__Expert 4350 points

    Sergej,

    Thank you for your interest in TI products.

    The default configuration for the device when it leaves the factory is available in the datasheet which can be accessed here:

    http://www.ti.com/product/TPS40400

    A summary follows:

    1) OPERATION

    OPERATION

    BIT

    7

    6

    5

    4

    3

    2

    1

    0

    Function

    ON

    X

    Margin

    X

    X

    Default

    0

    0

    0

    0

    0

    0

    X

    X

     

    2) ON_OFF_CONFIG

    ON_OFF_CONFIG

    BIT

    7

    6

    5

    4

    3

    2

    1

    0

    Function

    X

    X

    X

    pu

    cmd

    cpr

    pol

    cpa

    Default

    X

    X

    X

    1

    0

    1

    1

    1

    Result

    X

    X

    X

    Device does not power up until commanded by the CNTL pin and OPERATION command as programmed in bits [2:0] of the ON_OFF_CONFIG register.

    Device ignores the “on” bit in the OPERATION command.

    Device requires the CNTL pin to be asserted to start the unit.

    CNTL pin is active high.

    Turn off the output and stop transferring energy to the output as fast as possible.

    I believe this translates to give you what you want, which is that the OPERATION command is not required (bit 3), the CNTL pin needs to be asserted (bit 2), and the CNTL pin is active HIGH (bit 1).

    However, I would like to ask a few questions.

    - Will you be able to program the device after it is assembled to your board? You will need to because there are some default parameters that will likely not meet your requirements (like IOUT_CAL_GAIN and VOUT_SCALE_LOOP).

    - What sort of speed / bandwidth do you need for your adaptive voltage scaling? The output voltage can be margined and / or trimmed during operation, but that functionality was not meant to be used to improve transient response. The amount of time it takes to re-configure margin or trim would be too long for such purposes.

    Hope this helps.

    MC.