• State
  • Locked Locked
  • Replies 7 replies
  • Subscribers 62 subscribers
  • Views 148 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.

TPS61196: Prevent the IC from going into latched off when opening LED strings.

Simon Höglund
Prodigy 10 points
Part Number: TPS61196

Hi,

Is it possible to trick the TPS61196 that the LED strings are connected, when they in fact are open circuit? For example if I would apply a voltage (higher than the IFBV and lower than the V_LED_SHORT) to the IFB pins at the same time as I disconnect (open) the LED strings?

If possible, would I also have to do something with output voltage to keep it steady when LED strings are open to prevent OVP to kick in?

Kind regards, Simon

  • 0
    TI__Mastermind 24050 points

    Hi Simon,

    Do you mean you only need several of the 6 channels in your application? The unused LED strings will be detected automatically when the IC is powered on.

    BR

    Patrick

  • 0 in reply to Patrick Yao
    Prodigy 10 points

    Hi Patrick, 

    I only need 4 of the LED strings in regular operation, so 2 of them will be not be used at all. 

    However, my question is regarding the 4 that is in use. On my PCB I would like to be able to open all 4 LED strings at certain situations, and then reconnect them to the LED strings later on. I would like to do this to turn the LED strings off completely (turn the screen dark) and later on turn the LED strings on again (maybe hours later). And I must be able to do this without the circuit going into latched off mode. That is why I wonder if its possible to trick the circuit to think that it has LED strings connected to the IFB pins by applying a voltage at those pins. 

    I suppose there is other ways to turn the LEDs on/off, but in my situation I only have the IFB and output voltage at my disposal. That is why I wonder if its possible to trick the circuit in this way.

    BR, Simon

  • 0 in reply to Simon Höglund
    TI__Mastermind 24050 points

    Hi Simon,

    Understood. Theoretically this method is do-able to trick the IC. But the concern is the moment that you open the LED and connect the external voltage on IFB pins. Do you already have a schematic with this method added?

    BR

    Patrick

  • 0 in reply to Patrick Yao
    Prodigy 10 points

    Hi Patrick,
    No schematic yet. I have ordered a TPS61196 testbord. So, will start to test soon and see if I can get something working.

    How about the output voltage: If I open the LED strings, can I left the output voltage floating? Or would I have to tie it to ground through a resistor to keep a current?

    Br, Simon

  • 0 in reply to Simon Höglund
    TI__Mastermind 24050 points

    Hi Simon,

    The output voltage will still be regulated if you supply the IFB pins with proper voltage. You can try to left it floating first for your experiment.

    BR

    Patrick

  • 0 in reply to Patrick Yao
    Prodigy 10 points

    Hi Patrick,

    Thanks for the information.

    Regarding the soft start-up: the datasheet says "The device outputs a 20-ms pulse to detect the unused channels ". When the device sends out the pulse, what is it looking for to detect if channel is active or inactive? How does it distinguish between an open LED string and a normal LED string?

    BR, Simon

  • 0 in reply to Simon Höglund
    TI__Mastermind 24050 points

    Hi Simon,

    TPS61196 uses a 60-μA current source to detect the IFB pin voltage. If the IFB voltage is between 1 V and 2.5 V, the device immediately disables this string during start-up.

    BR

    Patrick