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TPS61175: Design confirmation

Marvin Cantos
Expert 6590 points
Part Number: TPS61175
Other Parts Discussed in Thread: TPS552872, LM25118, TPS61388-Q1

Tool/software:

Hi Team,

Good day. I am posting this inquiry on behalf of the customer.

I have used WEBENCH Power Designer since my requirements are as follows:

  1. 9-18V DC Input and I require an 18V DC Output
  2. Output current ranging from 5mA to 200mA

I am interested in the TPS61175 as I like the package, BOM count and price as shown in the design here webench.ti.com/.../SDP.cgi

My questions based on the simulations are:

  1. The efficiency below 20mA output current is not shown - is it possible to draw this current or less? Or is there a fixed minimum output current requirement?
  2. If I use 18V at the input, the output will still be 18V correct?

 

Thank you for your help.

Kind regards,

Marvin

  • 0
    TI__Genius 16245 points

    Hi Marvin,

    Thank you for reaching out.

    1. the device does not get a minimum output current requirement and at light load it works in PFM.

    It would be hard to calculation efficiency at PFM, maybe that's why the Webench can not show the efficiency.

    2. when Vin is close to Vout, the output voltage will be unstable due to the minimum on time limitation.

    The output ripple will be quite large and it is not recommended.

    3. If 18Vin to 18Vout is necessary, it is recommended to use a buck-boost converter, like TPS552872.

    TPS552872 data sheet, product information and support | TI.com

    Best Regard,

    Fergus

  • 0 in reply to Fergus He
    TI__Expert 6590 points

    Hi Fergus,

    Thank you for your response. Please see the feedback from our customer.

    Thank you for your reply.

    I'm finding it a bit odd that WEBENCH power designer suggested this boost converter when my Vin input ranged from 9V to 18V - any idea why? As it's a bit unreliable it seems?

    1. I also found the LM25118 buck boost - would this work as well? Unfortunately the BOM count is a bit high however (30pcs).

    2. Alternatively - I propose a different solution. My DC input will be either 9V, 12V or 18V. I would like to add a boost converter and for it to work only when the Vin is 9V. When Vin is 12V or 18V I want to bypass the boost converter and just output Vin (12V or 18V). Can you recommend suitable circuitry for this?

    Thank you for your help.

    Kind regards,

    Marvin

  • 0 in reply to Marvin Cantos
    TI__Genius 16245 points

    Hi Marvin,

    1. I think it makes a mistake. it will be odd to transfer from 18V to 18V.

    2. LM25118 is also Buck-boost and it is suitable.

    But it uses external MOSFETs and Diodes which take more space and cost.

    3. Right now we do not have such device with bypass function at 18V.

    one approach is to shut down the device at 18Vin and the upper diode can be a natural bypass.

    another solution is our designing device TPS61388-Q1, it will be RTMed next year, maybe will be too late for customre.

    Best Regards,

    Fergus