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Boost IC recommendations

Tsai Anson
Prodigy 120 points
Other Parts Discussed in Thread: TAS3251, LM5176, LM5156, LM5121

Hi,

I am looking for a boost IC.

The purpose is boost voltage of battery from 25,2V(6S2P) and  33.6V(8S2P) to 35V to provide PVDD to TAS3251.

Low battery voltage is 22.2V.

The current needs 5A ~ 8A  (adjustable).

Is there any model you can suggest to me?

Thanks.

  • 0
    TI__Guru 65470 points

    Hello Tsai,

    The recommendation is as well somewhat dependent on the maximum input voltage. If it is getting very close to the 35V output voltage (especially on the 33.6V battery, I would recommend LM5176 which is a buck-boost device.

    In the other cases, I recommend LM5156 but as the power is relatively high for a boost converter, I recommend to use 2 converters in a 2-phase configuration.

    In general you could as well try Webench for such a request.

    Best regards,
    Brigitte

  • 0 in reply to Brigitte
    Prodigy 120 points

    Hello Brigitte,

    I found three ICs from Webench. Which one do you recommend is more suitable for TAS3251? (low noise/ripple)

    Thank you.

  • +1 in reply to Tsai Anson
    TI__Guru 65470 points

    Hello Tsai,

    I think that the noise/ripple is heavily dependent on the external components and not that much from the controller.

    Nevertheless, LM5121 might be the best one as it can disconnect the output from the input when you disable the device. Normally in boost converters, the input voltage is always on the output as there is a direct path from input through the inductor and diode (parasitic diode in the transistor for sync ICs) to the output.

    Best regards,
    Brigitte

  • 0 in reply to Brigitte
    Prodigy 120 points

    Hello Brigitte,

    Can you help me check the schematic? and are there any suggestions for parts of M1,M2,M3,D1 and Dbst?

    Does NMOS need a heat sink?

    Because Webench does not have recommendations for these parts.

    Some parts are not clearly marked in specifications

    Thanks.

    bboost.pdf

     

  • 0 in reply to Tsai Anson
    TI__Guru 65470 points

    Hello Tsai,

    In general I recommend to add a filter to the current sense path as well as gate resistors to have the capability to add them later on.

    I did not calculate the external components, but all necessary parts seem to be available. Nevertheless, I recommend to go through the datasheet calculations.

    Possibly you might need parallel MOSFETs for the power, but Webench should give this information.

    As power dissipation is heavily dependent on the layout, it is hard to answer your question on the heatsink without guessing. If you have the capability to add a heatsink, it is better to have it prepared and not install it than the other way around.

    Best regards,
    Brigitte

  • 0 in reply to Brigitte
    Prodigy 120 points

    Hello Brigitte,

    I redrawn the schematic and added a filter on current sense path and added a resister on gate of MOS, please see if there are other suggestions, thank your help.

    BTW,

    How can I use 2x LM5121 in a 2-phase configuration to reduce output current?

    ex. use 2x LM5121 35V/4A   ->  35V/8A

    Can I parallel 2x LM5121 directly?

    3000.bboost.pdf

  • +1 in reply to Tsai Anson
    TI__Guru 65470 points

    Hello Tsai,

    For a 2-phase configuration you cannot only connect them together. You either need an ORing circuit on the output, this would mean that on converter is taking the full current until it gets into current limit and then the second one will start to operate as well.

    Another possibility would be a solution similar to the one in this app note: https://www.ti.com/lit/pdf/snva826

    Best regards,
    Brigitte