• State Resolved
  • Locked Locked
  • Replies 2 replies
  • Subscribers 63 subscribers
  • Views 306 views
  • Users 0 members are here
Support feedback
Options
Options
Related

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.

LP5522: CTRL input port observed to toggle during power on

asdf asdf2
Prodigy 150 points
Part Number: LP5522

Hi,

I have a custom board with the LP5522 being controlled using a microcontroller.  The microcontroller is controlling the CTRL input pin and Iset is set using an external resistor.  The LED output from the LP5522 is driving a LCD backlight.  I see on a scope after power is applied to my custom board, the CTRL input to the LP5522 toggle high then low again.  The microcontroller is set up to do nothing on this pin to debug the behavior.  It seems like the LP5522 part is driving the CTRL pin high during power up.  It then in turn reads its own CTRL input pin as being high and drives the LED output.  The result is that I see the backlight of my LCD briefly turn on then off again when I power on my board, even though the microcontroller is not sending any control commands.

Does the LP5522 drive the CTRL pin during power up and if so, is there a way to prevent the LED output from driving high during power up so it doesn't turn on the backlight on power up?  I've tried to put a 100k pull down on the CTRL input and that does prevent the backlight from turning on but it looks like it puts the LP5522 in a weird mode where the LED output doesn't follow the CTRL input (the LED output turns off prematurely resulting in a dimmer backlight brightness).  I am operating the LP5522 in non-programmed mode.

Thank you.

  • 0
    TI__Genius 12915 points

    Hi,

    There should not be a drive CTRL action when powering up, could you help to capture a plot of VDD/CTRL when powering up, and the work situation after you add pull-down resistor?

  • 0 in reply to Hardy Wu
    Prodigy 150 points

    Hi Hardy,

    Thanks for confirming the part should not be driving the CTRL pin when powering up.  I lifted the pin on the microcontroller connected to the CTRL pin and probed on the microcontroller pin when powering up and I see that the microcontroller is driving this line high for some reason and not the LED driver.  I'll have to figure out why my microcontroller is doing this for certain pins.

    Thank you.