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<TPS65631W> I_LIM(min) value at 50mA Load current

Kyongmi KIM
Prodigy 10 points
Other Parts Discussed in Thread: TPS65631W

Dear. TI

I'd like to calculate the max SW current on TPS65631W following the document  "Application note, SLVA372C"

The load current would be just max 50mA. 

I think that the I LIM(min) value should be changed from datasheet value (0.8A, min Switch current limit)

Because 0.8A as I LIM(min) must be the result from  TPS65631W  max recommended output current 200mA.

I'd like to use smaller inductor package not just recommended by TI

Because of lighter load current which is differ from TI original design.

Could you give me I_LIM(min) at 50mA load current?

I hope your comment.

Thanks.

  • 0
    TI__Intellectual 1065 points

    Hallo Kyongmi,

    The first thing to consider is the switch current limit ILIM, which cannot be changed by the user. As you correctly point out,  the value of ILIM was chosen to make sure that the TPS65631W can supply the maximum output current under the worst-case conditions. Please note that in the TPS65631W device the parameter ILIM refers to the valley current, not the peak current (see sketch).

    .

    The second thing to consider is the peak switch current of the application, which varies depending on a number of parameters, such as input voltage, output voltage, output current, switching frequency, and so on. The value of the peak switch current can be calculated using the application note you refer to. You can also use the Power Stage Designer tool from TI, which is easier.

    During start up and transient conditions, however, the peak switch current can be higher the value you calculate above, and your inductor can saturate if it is not big enough. I recommend you start with an inductor with a saturation current of at least 400 mA, but as always, YOU MUST PERFORM A FULL EVALUATION OF YOUR CIRCUIT BEFORE FINALIZING YOUR DESIGN. I strongly recommend you observe the inductor current waveforms during start up and a worst-case transient condition at the minimum input voltage, to make sure that the inductor does not saturate.

    In your application, with only 50 mA of load current, the start-up behavior will almost certainly determine the choice of inductor.