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LM3409: Switching current threshold without using the Iadj pin

Alex kelley
Prodigy 100 points
Part Number: LM3409

Hi,

I am looking to have 2 output currents that can be set via some user selection input. I'd like to switch between the two without adjusting the Iadj pin. I am using the Iadj pin for analog dimming and would like to keep as much of the dynamic range as possible.

Would it be possible to insert a small series resistor (that can be shorted out by a switch) between the CSP pin and the sense resistor? See below. 

This should allow me to switch between 600mA and 750mA.

If it is absolutely necessary, I can use the Iadj pin to accomplish this but I'd like to avoid that if possible.

Thanks,

Alex 

  • 0
    TI__Mastermind 28655 points

    Hello Alex,

    You could do something like that.  It may be difficult to keep the traces short and the layout tight though.  I may be better to use a 0.375 ohm resistor and switch in a 1.5 ohm resistor in parallel.  The layout would be critical though.  The routing for the 0.375 would be short and the routing for the 1.5 ohm pulled to Vin wouldn't be quite as critical though you still want it short with as small a loop as possible.

    Best Regards,

  • 0 in reply to Irwin Nederbragt
    Prodigy 100 points

    Hi Irwin,

    I think the parallel solution is a much better choice as it also allows me to reduce the current requirement of the inline switch.

    Thanks for the help!