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LP5861: Current consumption question

John Griffith
Mastermind 21543 points
Part Number: LP5861
Other Parts Discussed in Thread: LP5860EVM

Hello,

My customer is looking at the LP5861 device and has some questions around power consumption at low output currents. Their concern:

One concern might be the current drain, the first page in the spec sheet says the average current is 3 mA typical for 5mA of channel current, but the electrical spec table lists 4.3 mA for 5mA of channel current. Is the difference how the device's 5mA output current is programmed? For example, maybe it is is higher when current is limited by the global max current (MC) instead of individual dot current (DC)?

Is there anything that can be done to to minimize Icc?  Lastly, can we share any data on Icc for low (sub 1mA) channel currents? I don't see anything showing how this might vary with channel current in the datasheet. Customer plan is to run all the LEDs at around 0.5 mA, and they are hoping the IC current might go down with lower output currents. 

Thanks!

John

  • 0
    TI__Expert 6440 points

    Hi John,

    Nice to hear you!

    For the first question, sorry I don't quite understand what you want to ask, does the average current means Icc or current sink's average current? Do you want to know how to set output to 5mA by different configuration?

    Could you please give me some time to test the Icc value when output current set to 0.5 mA?

    And I will give you the feedback after this weekend. 

    Thanks!

    Ives

  • 0 in reply to Ives Li
    TI__Mastermind 21543 points

    Hi Ives,

    The first question is around the device's quiescent current. The numbers on the first page do not math the numbers in the electrical parameters table.

    and:

    We were trying to understand if those numbers are for different device settings. For example, what if one test was with global max current and the other was tested with individual dot current. Not sure, but 3mA to 4.3mA is a fairly big difference for a battery powered application.

    Please let us know if you can think of any device settings / ways to program the device that would ensure the lowest possible device current. Thanks for taking some data on ICC with outputs set to 0.5mA! That will really help with the customer. 

    John

  • 0 in reply to John Griffith
    TI__Expert 6440 points

    Hi,

    When customer set current to 0.5mA, Is their VCC setting to 3.3V?

    Thanks!

  • 0 in reply to Ives Li
    TI__Mastermind 21543 points

    Yes, please do the testing with VCC of 3.3V for 0.5mA drive current on the outputs.

    John

  • 0 in reply to John Griffith
    TI__Expert 6440 points

    Hi John,

    Because I only have LP5860EVM, so I test it in 1-scan mode, which has the same operation compared to LP5861.

    My configuration is:

    Vcc = 3.3V, Global Maximum Current = 3mA, PWM Percentage = 100%, DC = 0x50, Iout = 0.47mA. (For all LEDs on SW0)

    At this test condition:

    Icc = 4.0027mA.

     

    Thanks!

    Ives.

  • 0 in reply to Ives Li
    TI__Expert 6440 points

    Hi John,

    For another question, I also do a test on LP5860EVM by 1-scan mode

    My configuration is:

    Vcc = 3.3V, Global Maximum Current = 10mA, PWM Percentage = 100%, DC = 0x19, Iout = 0.49mA. (For all LEDs on SW0)

    At this test condition:

    Icc = 4.3721mA.

    So, the Icc is related to the value of Global Maximum Current but not the output current.

    Thanks!

  • 0 in reply to Ives Li
    TI__Mastermind 21543 points

    Hi Ives,

    Thanks for taking this test data! Do you have any idea how the front page typical number of 3mA is done with 5mA for channel current? This is listed as a sub-bullet of "Ultra-low power consumption" on the front page of the datasheet: 

    Active mode: ICC = 3 mA (typ.) when channel current = 5 mA

    Your testing, with lower output channel current is resulting in more current than the datasheet advertises. It seems like we might be missing some other setting to further optimize supply current to the IC...

    John

  • 0 in reply to John Griffith
    TI__Expert 6440 points

    Hi John,

    Icc is also related to PWM frequency setting, in the above test I set its value to 125kHz,

    and I do another test to set:

    Vcc = 3.3V, Global Maximum Current = 3mA, PWM Percentage = 100%, DC = 0x54, Iout = 0.5mA. (For all LEDs on SW0)            Data Refresh Mode = mode1, PWM frequency = 62.5kHz.

    In this test condition,

    Vcc = 3.6825mA.

    When I set Data Refresh Mode to mode3 and set current to 5mA, Icc=3.7082mA.

    When I set Data Refresh Mode to mode2 and set current to 5mA, Icc=3.6819mA

    I also tried to change other configurations, but it seems the Icc is only affected by global maximum current, data refresh mode and PWM frequency.

    Thanks!

    Ives.

  • 0 in reply to Ives Li
    TI__Mastermind 21543 points

    Thanks! Just sent this to the engineers, will let you know if there are any follow up questions.

    John

  • 0 in reply to John Griffith
    TI__Mastermind 21543 points

    Hi Ives,

    Can you confirm that with 100% duty cycle that there is no switching on the outputs? It is purely a DC current with no chopping? Customer is concerned about noise from switching and does not want any PWM on the output. I believe this is how the part works but just want to confirm. 

    Is there a way to use an external resistor to have the global MC current setting be less than 3mA? For example, could they set it to 0.5mA or 1mA? 

    John

  • 0 in reply to John Griffith
    TI__Expert 6440 points

    Hi John,

    For the 1st question: yes, when you set PWM to 100% duty cycle, there is no switching on the output.

    For the 2nd question: no, LP586x family don't have Iset pin to use an external resistor to set MC current, it can only be configured by register value.

    Thanks!

    Ives

  • 0 in reply to Ives Li
    TI__Mastermind 21543 points

    Ives,

    Thanks for all your help! Last thing (I hope!). Looking at the ABS MAX table, all of the pins are rated to 6V. Does this mean that all pins have blocking and it is okay for a voltage to exist on the pins even if VCC is not powered for the device? 

    John

  • 0 in reply to John Griffith
    TI__Expert 6440 points

    Hi John,

    Yes, all pins can connect to a voltage below 6V directly.

    Thanks!

    Ives