LMR14030 Application

Jerry Tang

Intellectual 440 points

Other Parts Discussed in Thread: LMR14030

Hi,

Using the LMR14030 for a buck converter,the expected output power is 10W(5V/2A),

How to calculate the minimum input voltage for this application?would you please provide

a formular for me?

Thanks!

over 8 years ago

0 JohnTucker over 8 years ago

TI__Guru**** 191445 points

Moving to the Simple Switcher forum...but you can get the information you need by looking at the drop out curves of Figures 7, 8 and 9 of the datasheet.

0 Jerry Tang over 8 years ago in reply to JohnTucker

Intellectual 440 points

John,

Thanks! But there are no dropout curves in the datasheet for some parts,please tell me how to calculate it for this case.

0 JohnTucker over 8 years ago in reply to Jerry Tang

TI__Guru**** 191445 points

I personally checked that the curves are in the LMR14030 datasheet. It looks like it is measured data rather than a calculation. It may be different for other devices. What other devices are you concerned with?

0 Jerry Tang over 8 years ago in reply to JohnTucker

Intellectual 440 points

Hi John,
If the output voltage changed to 4V,not 5V,or other value,I'm afraid that the curves in the datasheet is no longer reasonable.
How to get the minimum input voltage in this condition?
Thanks!

0 Luke Pan over 7 years ago in reply to Jerry Tang

TI__Intellectual 2790 points

Hi Jerry,
The dropout voltage varies with many facts. Such as frequency, inductance, inductor Rds_on, inductor resistance. You can use below equation for an estimated calculation:
Vin=Vo+Io*(Rds_on+RL)+(1-Dmax)*(Vd+Io*RL+Vo)/Dmax
Rds_on: High side FET on resistance
RL: indictor resistance
Vd: diode forward voltage
Dmax=1-Toff_min/(6*Ts) for frequency lower than 1MHz, Dmax=1-Toff_min/(11*Ts) for frequency higher than 1MHz.
Toff is 120ns typically. Ts is period of a switching cycle.
BR
Luke

0 Jerry Tang over 7 years ago in reply to Luke Pan

Intellectual 440 points

Hi Luke,
Why does the Dmax vary with different frequency? Is the Toff same for other devices?

0 Luke Pan over 7 years ago in reply to Jerry Tang

TI__Intellectual 2790 points

Hi Jerry,

Toff_min may become larger when switching period (Ts) increases. but it's not as large as Ts in proportion. That's why Dmax varies with frequency.

Luke

Power management

Power management forum

LMR14030 Application