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LM3414HV: Operating Duty Cycle (D) minimum and maximum value

Amit Tandel98
Prodigy 230 points
Part Number: LM3414HV
Other Parts Discussed in Thread: LM3409

Hi,

On page 18 of the datasheet, there is mention of Operating Duty Cycle as given below.

To calculate component values the operating duty cycle (D) must be calculated using D = Vled / Vin.

1) Is there any limitation on value of D?

2) What should be its (D) minimum and maximum value? Why?

3) Can we have Vled = Vin? I.e. same voltage output of transformer as input voltage of LED strips.

4) If Yes, what will be the pros & cons?

5) If No, why?

Thanks & regards,

Amit

  • 0
    TI__Intellectual 2590 points

    Amit,

    Regarding maximum duty cycle, this is a low side buck (or sometimes called buck to battery) topology.  Given it is a low side drive there is no physical limitation on maximum duty cycle.  I also do not see a maximum duty cycle specification, so it should be able to operate at very high duty cycles if not 100% even. 

    Regarding minimum duty cycle, this is a function of the leading edge blanking circuit and is described in the datasheet in section 7.3.2 Minimum switch on-time.  The typical value in the EC table is 400ns, therefore the minimum duty cycle would depend on the switching frequency as duty cycle is ON-time/Frequency.

    You will have to test 100% duty cycle on this device as I'm not sure it can accomodate that with it's control method.  If it does not work, we have a high side PFET controller (LM3409) that definitely can accomodate 100% duty cycle in a buck converter.

    -JP