• State Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 1 answer
  • Subscribers 62 subscribers
  • Views 216 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

LP5036: Current-limiting resistors?

user6282955
Prodigy 20 points
Part Number: LP5036

Apologies if this is answered in the datasheet, but it's not entirely clear to me. When using the LP5036 with RGB LEDs, do we also need current-limiting resistors, or does setting the IREF value properly ensure that the LEDs won't go out of control?

(If it makes a difference, I'm using 4.4v supply to the LEDs, and R, G, B channels have 1.9v, 3.3v, 3.3v forward voltage respectively. So I was putting resistors between the LED cathodes and the LP5036 channels using standard calculations (120, 56, 56 ohms), but dropping 36 parts off my BOM would certainly be nice.)

Thanks very much for any help.

  • 0
    TI__Genius 12915 points

    Hi,

    Yes resistor between IREF and GND is necessary. Maximum output current is controlled by it. For the proper value, you can find the detail equation at page 18 section 8.3.3 of datasheet. It depends on the output current you want to set.

    For the resistors between LED cathodes and channels, it is suggest left around 0.5V at channel pins, because the saturation voltage at output pins is around 0.4V and it should be satisfy to ensure output current accuracy. Also it is OK not use them.

  • 0 in reply to Hardy Wu
    Prodigy 20 points

    I'm not sure I understand. Between the LED cathodes and the channel pins, should I use a resistor as normal (given the standard resistor LED calculation), omit a resistor, or use a resistor that leaves an extra 0.5V of forward voltage?

    I am aware that the IREF resistor is necessary, and that's already in my schematic.

    Thanks very much for your help.

  • 0 in reply to user6282955
    TI__Genius 12915 points

    Hi,

    The easiest way is not adding the resistor between LED cathodes and channel pins. The LED current was set by IC so resistors have no function here.

    VLED (in your case is 4.4V) is equal to Voltage on channel pins + Voltage drop on resistor + LED forward voltage. Voltage on channels should at least be 0.4V when calculating the resistors value.