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TPS650860EVM-116: Power slews down timming

Shih Scott
Prodigy 70 points
Part Number: TPS650860EVM-116

Hi

I have an experiment about power up and down sequence control by SMPBUS of the TPS650860EVM-116. During the power up it's all right, but power down has a few problems. Buck2 & 1 have slews down time more than estimated.(Register setting slews dowm)

According to the datasheet formula it should end in 2ms, but it's over 40ms, refer to the figure below. Is it normal, or there is a way to improve it?  

  • +1
    TI__Mastermind 26110 points

    Hello, 

    Thank you for reaching out via E2E. The dynamic voltage scaling (DVS) feature you reference in your post is used to slew up and down when adjusting the output voltage value. This feature is not used during the power down sequence. 

    The device does have internal discharge resistors for all the rails, which can be configured via I2C to speed up or slow down discharge at power down. The specific register for BUCK1 & 2 control is DISCHCTRL1 register (address 40 hex). The section on this register from the datasheet is shown below.

    Best Regards,

    Garrett 

  • 0
    Prodigy 70 points

    Hi, Garrett 

    Appreciate the reply. How does the discharge resistor work in the internal circuit? I can't find the related document or formula.

  • +1 in reply to Shih Scott
    TI__Mastermind 26110 points

    Hello, 

    I am not able to share too much detail on the internal circuity of the device. The way the internal discharge resistors work is that they are automatically connected from the rail to ground when a rail is turned off (assuming the discharge resistor feature has been configured via I2C), and then automatically disconnected when and output rail is enabled. 

    Best Regards,

    Garrett

  • 0
    Prodigy 70 points

    Hi,

    The reply relies helpful on, and I think we can figure out the rest of issue.