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LP5860: Controlling higher power led using the LP5860

Nir Dvash1
Intellectual 470 points
Part Number: LP5860
Other Parts Discussed in Thread: TLC59711

Hey Guys,

I got 192 high current LEDs (200mA each) which I wish to control using this device, is there some way to bypass its maximum 50mA per current sink?

For example let the device control a FET and have that FET control the LED?  This is needed since I may have a sink which needs to light up a few leds each running at 200mA and

so can easily reach current of 1A or more.

Thank you,

Nir.

  • 0
    TI__Genius 12915 points

    Hi Nir,

    One thing to confirm that do all 192 high current LEDs need to be controlled independently, or several LEDs are cascade?

    Yes the device can be used as FET gate driver, to control the external high current FET. A pull-high resistor is necessary, since the outputs are open drain scheme.

  • 0 in reply to Hardy Wu
    Intellectual 470 points

    Hello Hardy,

    Thank you. Yes, each led should be controlled independently.
    Would you be so kind and show me an example schematics of how this connection to a high current FET might look like? If you can also
    give an example of such a FET that might work well it will be great. 
    Nir.
  • 0 in reply to Nir Dvash1
    TI__Genius 12915 points

    Hi Nir,

    Here is the draft schematic for your reference. If you want to control the LED as the same logic with output channel, 2 NMOS need to be used. When the channel off, the gate of 1st NMOS is pulled high and 1st NMOS is opened, then the gate of 2nd NMOS is pulled down and the 2nd NMOS is turned off, thus the LED is turned off following the output channel.

    The selection of FET is related to your current requirement and VLED supply. I think you could find much suitable devices in TI.com.

  • 0 in reply to Hardy Wu
    Intellectual 470 points

    Hey Hardy,

    Thank you very much. A few questions that popped into my mind:

    1. Will I still be able to use the device to its fullest (i.e. controlling 192 individual leds) or when you wrote "Yes the device can be used as FET gate driver" you meant I will be able to use its 18 current sink outputs to drive only 18 leds?

    2. If I will be able to use the device to its fullest, wouldn't I need to add external high current fets also on each of its High-side PMOS switch outputs?

    3. Will using a pull up resistor on the open drain outputs won't distort the PWM signal because of the relatively high rise time the resistor will force on the signal?

    Thank you,

    Nir.

  • 0 in reply to Nir Dvash1
    TI__Genius 12915 points

    Hi Nir,

    Sorry that I did not make my point clearly. I do not think the fullset 198 dots can be used. Only 18 current sink outputs can work as gate driver.

  • 0 in reply to Hardy Wu
    Intellectual 470 points

    Oh! I'm glad I asked!

    In this case, I think I will just take the TLC59711 and cascade those. 

    Thank you,

    Nir