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LP8861-Q1: LP8861-Q1

Kevin Kinion54
Prodigy 120 points
Part Number: LP8861-Q1

I would like to use this part down to 10mA per output.  The data sheet specifies Riset = 2342/(Iout - 2.5) and states that the maximum Riset should be 129Kohm.  However, on the development board user's guide the value of Riset is given at Riset = 2000/(Iout-2.5).  It also shows the a graph where Riset exceeds 140K with an Iout of about 10mA.  Which is it?  What can I realistically do?  The maximum current for the LEDs specification is 20mA.  I have them in strings of 8 LEDs.

  • 0
    TI__Expert 5475 points

    Hi Kevin,

    Firstly, sorry for the confusion on the calculation equation of  Riset. Actually the equation in the EVM user's guide is right, as shown below. Theoretically, the device can be used at 10mA current per channel. It's just the current accuracy may not be very good. And the current accuracy cannot be guaranteed.

  • 0 in reply to Shirley He
    Prodigy 120 points

    Thank you for your response.  So, just to be clear, according to the calculation you provided, I can use a 240Kohm resistor to get my 10mA (though not accurate).  The data sheet recommended maximum value is 129 Kohm which would get me 19mA (too much!).  I'm OK with 20% or even 30% inaccuracy as long as its reasonably close to 10mA.  So 240Kohm resistor for Riset is OK?   

  • 0 in reply to Shirley He
    Prodigy 120 points
    Thank you for your response. So, just to be clear, according to the calculation you provided, I can use a 240Kohm resistor to get my 10mA (though not accurate). The data sheet recommended maximum value is 129 Kohm which would get me 19mA (too much!). I'm OK with 20% or even 30% inaccuracy as long as its reasonably close to 10mA. So 240Kohm resistor for Riset is OK?
  • 0 in reply to Kevin Kinion54
    TI__Expert 5475 points
    Hi Kevin,

    You can use a 240kohm resistor to get around 10mA current. The current accuracy has not been simulated and validated. It is possible to be 20% or even 30%.