voltage divider ?

i'm driving LED with a PAM2861 chip at 350mA with 12 volt source. i'm also using a dimming feature by putting low voltage on the VSET pin. i'm using 10k and 1k resistors in the divider to get 1.09 volts to put on VSET pin and it's working fine. i'm unsure of the size of resistors i should be using. should i go to higher or lower value resistors or are these ok. thanks

Those resistor values are fine. They will draw just over 1 mA. Running a single LED at 350 mA probably draws nearly 100 mA from the supply, representing a 1% loss. Unless you are super concerned about efficiency, this is trivial. If you are driving more than one LED in series, it's an even smaller percentage loss.

The input current on the Vset pin is typically 8 uA (probably less the way you are using it), which would give an error of 0.0072V in your setting, using these values. Using higher values would decrease the efficiency loss, but increase the error in Vset, and vice-versa.

Edit: The two resistors combined will dissipate around 0.013W, so the power rating of the resistors is not important. Use whatever is convenient.

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with this design, the LED doesn't dim all the way down before going off completely. it does get dimmer but remains pretty bright and then goes off all at once. i need it to dim all the way down to nothing. am i doing something wrong? thanks

Yes, you can only dim it to 12% this way, then it switches off. To go lower (down to 1%) you need to use a PWM control. See the post I made a few minutes ago in this forum in the thread titled "Driving a 10W High Power LED with CC/CV with PWM???"


The pin description in the data sheet suggests PWM frequency less than 500 Hz.