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TPS61500 start up

treez
Intellectual 970 points
Other Parts Discussed in Thread: TPS61500, TPS61165

Hello,

I wish to do a LED driver for 13.5 Volts input.

It should power seven series white LEDs at 300mA.

The TPS 61500 looks like it fits the bill here.

However, there is one problem.

The TPS61500  has an internal  switch current detect which doesn't shut the switch off until the switch |(FET) current is 3.5A.

....so this means that on start-up, my inductor will saturate, since it saturates at 2.1A.

I know that the soft start will mitigate this.

...however, when the power is cycled on/off/on, the soft start capacitor will still be charged at the second "on-coming", and the soft start will not happen.

 

Sp please could you suggest a controller which will deal with this problem and not allow my inductor to saturate at start-up?

  • 0
    TI__Mastermind 36110 points

    You should always select the correct inductor parameters.  Also note that some inductors have a very soft saturation curve which means they will still work in this application if the current goes above their rated saturation current.  You should measure the inductor currrent at startup with your specific conditions.  Also note that the TPS61500 datasheet states that the softstart capacitor is discharged through a 5kohm resistor 10ms after the EN voltage goes low.  If you are turning the IC on and off faster than 10ms, then you can connect a schottky diode with the anode connected to ss and cathode connected to the EN voltage so that when EN goes low, it actively discharges the ss cap.  You should also consider the TPS61165.