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Very light load isolated power

Ross Johnson
Prodigy 230 points
Other Parts Discussed in Thread: SN6501, TPS55010

Hello,


I need an isolated DCDC converter to provide 3V3 @ up to 5mA. The idle load will be only around 100uA, and the primary side power budget is an average load of just 250uA. So Quiescent supply and minimum load are important factors.

Is the SN6501 a suitable choice? It has a typical no load current of 150uA, but it's hard to tell from the data sheet what the total supply current would be for a load of 100uA as the efficiency curve (page 1) tends to 0% as the load approaches 0.

Another option may be the TPS55010, which has a higher quiescent supply of 360uA. This figure is sufficiently low that together with the convenient  enable and soft start features would make power cycling a viable option as a typical duty cycle would be around 10% active.


Are there better chips for my application? Perhaps for such a low maximum load, capacitive or optical solutions might be adequate?

Thanks, Ross

  • 0
    TI__Intellectual 2200 points

    Hi Ross,

    The SN6501 is stable at low loads. Used with an output LDO to ensure a tight output voltage control, SN6501 is a good choice. I don’t have exact numbers for the power consumption at low loads, but it will be the sum of the quiescent current from SN6501, the current taken to charge the parasitic capacitors of the transformer, and the core losses in the transformer. If you really need to know a value for the supply current at low-current load case, and if you can pick a transformer and LDO configuration from the SN6501 datasheet, we might be able to do some measurements in the lab. The efficiency will be poor at low loads, as indicated in the datasheet, but otherwise there’s no problem with this configuration. One benefit of SN6501 will be the ready availability of transformer choice.

    For a discussion on the TPS55010, could you please raise a query on the power management forum below:

    http://e2e.ti.com/support/power_management/isolated_controllers/

    Rgds,

    Anant