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CSD97395Q4M: CSD97395Q4M component design efficiency for low loads(100-150mA) ?

Part Number: CSD97395Q4M
Other Parts Discussed in Thread: BQ500215

Hi

I am using CSD97395Q4M like the typical application as power Stage for wireless charger with some parameter changes.

I want to know what is efficiency that this component is design to be with low current load ?(100-150mA]- no need expertly number(range).

thx

Ofer Shapira

  • Hi Ofer,

    The power loss will be mainly affected by the driver loss and switching loss here since the load current is extremely low.

    For example, if Vout=1V, and Iout=0.1A, then the Pout is only 0.1W, the driver and switching loss is depending on switching frequency which I don't have exact number under such low current condition, my guess wound be around 0.2~0.4W if frequency around 500-600kHz, so the efficiency probably not very good with such light load if switching frequency is high. The loss can be reduced if switching frequency reduces for such condition.

  • Hi,

    A little more details to sharpen the question:

     I am using bq500215 bqTESLA Wireless Power TX EVM (CSD97395Q4M include in the design) as see as your application -minor changes.

    The PWM_A=PWM_B=130KHz, do you mean to improve the efficiency I need to reduce the frequency?,It possible ?,what is the minimum ?

    Still you don’t have number range of efficiency for low current load?.

    thx

    Ofer Shapira

  • Hi Ofer,

    As I mentioned before, the power loss of CSD97395 under extremely light load is dominated by driver/switching losses. So theoretically the efficiency for the power stage only (it might be different case if you consider the whole system) can be improved if switching frequency is lowered and operate the power stage in discontinuous conduction mode (DCM) at very light load. I am not familiar with BQ500215 controller, you may not be able to change the frequency if the controller has fixed frequency structure.

    The minimum frequency setting is depending on your system design, to meet your system specs, such as voltage/current ripple and transient responses, etc.

    In user guide of "bq500215 bqTESLA Wireless Power TX EVM (Rev. A)", the figure5 provided some typical efficiency data for the EVM, have you checked this efficiency chart? Also in the BQ500215 datasheet you can find the efficiency data for the system.  CSD97395 has same voltage/current rating as CSD97374, the power loss should be very similar.