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lm3509: Proper use for LM 3509?

Ed Hepler
Expert 1940 points
Part Number: LM3509

I'm looking for a way to control the brightness of LEDs of various colors.   (PWM is not an option due to possible sensor sensitivity to strobing).

I'd like to use the LM3509 as a current source to the anodes of a number of different LEDs with an analog mux to select one cathode to send back to the LM3509 main (or sub) sink.   

I'm thinking I should be able to control the current source (hence the brightness) by sending control information to the LM3509...

Can it be used in this way?

Thanks!

  • 0
    TI__Intellectual 1040 points

    I'm not sure I understand the question correctly, but maybe this will help.  The LM3509 is designed to have the boost output connect to a common (Anode) for the LED string(s).  The cathodes connect to the current sink inputs.  The boost regulates the top side of the current sinks to ensure the current sinks do not run into dropout.  The current sinks regulate the LED current (separate control loops from the boost).  You can skip using the boost and just connect LED strings to the current sink inputs and control their current via I2C.  Just need to make sure the current sink input voltage stays above 0.4V.

    Thanks

    Travis