• State
  • Locked Locked
  • Replies 5 replies
  • Subscribers 62 subscribers
  • Views 960 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.

LM3414 used for 10% dimming

Kai Hsiao
Guru 12675 points
Other Parts Discussed in Thread: LM3414

Dear Sir 

If I use LM3414 for 10% dimming ,the output current maybe under 350mA 

so in this condition ,I can't use LM3414 for 10% dimming ,due to the output current will be under 350mA and over SPEC ,is it right ??

Thanks 

  • 0
    TI__Mastermind 25500 points
    You can analog dim the LM3414 below 350mA. You just want to make sure you stay in CCM operation for the current to be accurate, so it may require a higher inductor value. If you need to dim further the LM3414 can PWM dim to a very low average current level.
  • 0 in reply to Clinton Jensen
    Guru 12675 points
    Dear Jensen

    Thanks for your reply

    I have a little confused , you mean LM3414 can use analog Dim to do iout<350mA ,why datasheet shows LED current from 350mA to 1000mA
    You also mention PWM Dim to do very low average current ,what's different between analog dim ,seems like the result is the same that LM3414 can do Iout < 350mA

    if I use PWM dim and duty is 10% ,I think the average current will be under 200mA ,
    What's the risk I need to take care??

    Thanks
  • 0 in reply to Kai Hsiao
    TI__Mastermind 25500 points

    I am not sure why they say 350mA in the datasheet. There is a graph of ILED vs RIADJ in the datasheet that shows you can set it as low at 100mA. We have done this and so have other people. You just need to make sure you are in CCM (inductor current never falls to zero) so it may require a higher inductor value. The equations are in the datasheet. You can also analog dim (also see datasheet) down to 100mA.

    In either case you can dim much lower using PWM dimming. In fact you can go very low. For example, you choose RIADJ for 350mA output (or whatever you choose, but 350mA for this example) and the average LED current is approximately the duty cycle times the max LED current. So if you use a 10% duty cycle in this case the average LED current is 35mA.

  • 0 in reply to Clinton Jensen
    Guru 12675 points
    Dear Jensen

    Thanks for your reply

    e2e.ti.com/.../253019

    Above link say that if the output current under 350mA ,LM3414 will have widening of the tolerance of the average LED current (I can't make sure this is true)
    So we would like to know ,if the average current is 35mA for 10% dimming ,how is the tolerance ??

    Thanks
  • 0 in reply to Kai Hsiao
    TI__Mastermind 25500 points

    The tolerance suffers a bit at lower currents because the error amp offsets become a higher percentage of the total current sense voltage. PWM dimming will not have that issue, the accuracy will not suffer. That is one reason it is often chosen for wide range dimming.