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LP8555: What is maxium delta voltage between each string in one port and LED qunatity that can support

user5923617
Prodigy 110 points
Part Number: LP8555

Hi

I am using a LP8555 to driver 2 LED bars, LED bar informatin as below picture.

1)String LEDA6 will have longer trace than other 5 strings in port A. So the Vf will be a little higher than others.

   What is the max delta value between the 6 strings in one port that LP8555 can handle? Especially considering LEDA6 Vf caused by longer trace.

2)What's the maxium quantity of LEDs that LP8555 can support?

3)For the thermall, I find form the aplication note that Tj=Ta+（Rθja*power）.Here power means total power of the LED bar or power of each LED string?

Thanks.

  • 0
    TI__Genius 14295 points
    Hi,

    Proper engineer has been assigned to take a look at this and will reply you soon.

    Due to Chinese new year holidays, response maybe delayed.

    Thanks for your understanding.

    Regards,
    Kenneth
  • 0
    TI__Mastermind 22745 points
    Hi ,
    1). That depends on the real application and LED configuration, The main consideration for this is about the current sink voltage rating and thermal (efficiency), the different volatge among those channels will drop on the current sink, it will decrease the efficiency.
    2). The maximum output voltage is 28V, so you need to make sure the output voltage not exceed 28V;
    3). That should be the total power.
    Regards
    Sean
  • 0 in reply to Sean Zhou
    Prodigy 110 points
    Hi Sean
    Thans for the reply.
    1)In my LED configuration , the Vf of LED=5.6V， 4 LEDs per string ， there are total 6 strings used in port 1.
    The total Vf/string=22.4V. String 6(LEDA6) maybe 22.9V due to longer trace(Just for example).
    In this case , there is 0.5V delta among the strings in port A. Will this lead to un-uniform current among strings?
    Or the driver just raise output voltage to 22.9V and keep the current the same?
    2)&3)
    Considering the max output voltage is 28V, in my design Vf/string =22.4V(5.6V/LED, 4LEDs/string), not exceed 28V , so it is OK correct?
    I am using total 11 strings in portA and portB. So total 44 LEDs. Not exceed 28V.
    However if considering the thermal, Tj=Ta+（Rθja*power), if Ta=25°， Rθja=70°， power=2.96W（12mA/LED*5.6V/LED*44LEDs）,
    Tj will over 150°， then driver will shut down， correct？
    Any suggestion about this to driver 44LEDS in one driver?
  • 0 in reply to user5923617
    TI__Mastermind 22745 points
    Hi,
    1). for 0.5V delta voltage among the string, it is ok, it will not lead to un-uniform current among strings.
    2). the voltage should be ok;
    3).For thermal consideration, it really depends on the real application and environment, you'd better to carefully layout the devices and leave the thermal flow path. I think it should be ok.You'd better to measure the thermal performance with realy circuit.
    And please help me to click "resolved"for me. Thanks.
    Regards
    Sean
  • 0 in reply to Sean Zhou
    Prodigy 110 points

    Thank  you Sean.