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TPS55289: Current Limit and Vsns

Mahboob Khan Mohammed
Prodigy 245 points
Part Number: TPS55289
Other Parts Discussed in Thread: INA180

Hello,

I am trying to figure out how the current limit feature works on this device. The datasheet presents an equation which involves 3 variables, Rsns, Vsns, and Iout_limit.

How do you calculate Rsns for an output current 5A? Is there a constant value that should be used in place of Vsns?

Rsns is required to limit the current or can the current be control through I2C commands?

I need the design files for this product for reference, where can I find it?

  • 0
    TI__Mastermind 22350 points

    Hi Mahboob,

    Thanks for reaching out on E2E. 

    I will look into this and reply on Monday.

    Regards,

    Bryce

  • 0
    TI__Mastermind 22350 points

    Hi Mahboob,

    May I know the below info about this project? Please send this to my email so I can send the design files(sch, pcb) to you.

    Customer and project name:

     

    Application and product type:

     

    Mass production time:

     

    The life cycle:

     

    Annual dosage:

     

    For TPS55289 which is a I2C version device, the Vsns (VISP-VISN) can be programmed by writing to IOUT_LIMIT register. And Rsns is fixed since it is solded on board, so the output current can be determined by Vsns/Rsns.

    Regards,

    Bryce

  • 0 in reply to Bryce Xun
    Prodigy 245 points

    Hi Bryce,

    Thank you for the reply. I have forwarded the information you requested via direct channel.

    Another question I had was how would you achieve the maximum current limit on this part? Just by disabling the current limit through IOUT_LIIMIT register will do the trick or do you need to exclude the Rsns resistor from the board? and what is the maximum current limit, is it 6.35A or 8A? because datasheet specifies 2 limits a 6.35A programmable limit and an 8A average inductor limit.

  • 0 in reply to Mahboob Khan Mohammed
    TI__Mastermind 22350 points

    Hi Mahboob,

    Thanks for your feedback.

    Yes, this device has output current limit and average inductor current limit which would limit the maximum current of this part.

    For output current limit, if you set VISP-VISN to 63.5mV and you choose Rsns=10mohm, you can disable this function or get max 6.35A output current limit. Also, if you choose smaller Rsns, the ouptut current limit can be larger.

    For average inductor limit, it is fixed and can't be programmed. For Buck mode, the average inductor current equals to output current; for Boost mode, the average inductor current equals to input current.

    Regards,

    Bryce

  • 0 in reply to Bryce Xun
    Prodigy 245 points

    Hi Bryce,

    Thank you for the clarification.

    I am waiting for the design files for the EVM board. It would be great if you can send it to me.

    Thanks,

  • +1 in reply to Mahboob Khan Mohammed
    TI__Mastermind 22350 points

    Hi Mahboob,

    Please check your message, I will close this thread, please let me know if you have more questions.

    Regards,

    Bryce

  • 0 in reply to Bryce Xun
    Prodigy 245 points

    Hi Bryce,

    Your last comment does answer the precious question. I have another question that is related to this one.

    Since this device doesn't have any means to transfer the real time output current measurements to a micro through I2C, we are needing to measure the output current using an external current sense amplifier (e.g. INA180).

    The INA requires a shunt resistor and we already have one shunt resistor that is being used by the TPS at the ISP and ISN pins, so, is it recommended to use the same resistor to feed the input of the INA.

    Something like shown in the picture attached.

    Thanks,

  • 0 in reply to Mahboob Khan Mohammed
    TI__Mastermind 22350 points

    Hi Mahboob,

    TPS55289 used CDC pin which outputs a voltage proportional to the output current, you can also find from datasheet page20.

    Regards,

    Bryce