LP8861-Q1: different Iset current formula

F_F_S

Part Number: LP8861-Q1

Hi,

I don't understant why there are two different formula to calculate Iset current:

LP8861-Q1 datasheet : into 8.3.3.2 Equation 3 RISET= 2342 / (IOUT-2,5)

on Using the LP8861-Q1EVM Evaluation Module document paragraph 8.2 current setting is ILEd=2000X VBG /Riset for example on my application with 20mA for channel The Riset can be 120K or 134K. What is it the right formula? Do you have an excel file to calculate all value of LP8861 for my application ? 4 led driver @20mA for channel with Vin=24V. Thanks

over 6 years ago

0 David Diaz Quintana1 over 6 years ago

TI__Intellectual 1235 points

Hello Floriano,

Both equations could be used within the optimum ILED range (for good rise time and current matching). As you operate at lower ILED currents then the difference between both equations is more noticeable. Both equations should yield similar results from ~30-40mA to 100mA (where current matching and rise time is expected to be good). So, it may be good to keep in mind that 20mA is pushing a little bit the limits for which some aspects of its performance may not be the best (but IC should still work well). For lower current levels I think that you could use ILED=2000xVbg/RISET equation.

Kind Regards,

David

0 F_F_S over 6 years ago in reply to David Diaz Quintana1

Prodigy 140 points

Thanks a lot for the reply.

Do you have an excel file to calculate all values of LP8861 for my application?

0 David Diaz Quintana1 over 6 years ago in reply to F_F_S

TI__Intellectual 1235 points

Hi Floriano,

What is exactly what you are trying to compute with the excel file you are asking?

Kind Regards,

David

0 F_F_S over 6 years ago in reply to David Diaz Quintana1

Prodigy 140 points

the input components as Risense, mosfet, inductor and diode

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LP8861-Q1: different Iset current formula