Datasheet

LM48511
www.ti.com SNAS416G –JULY 2007–REVISED MAY 2013
CALCULATING REGULATOR OUTPUT CURRENT
The load current of the boost converter is related to the average inductor current by the relation:
I
AMP
= I
INDUCTOR(AVE)
x (1 - DC) (A) (12)
Where "DC" is the duty cycle of the application.
The switch current can be found by:
I
SW
= I
INDUCTOR(AVE)
+ 1/2 (I
RIPPLE
) (A) (13)
Inductor ripple current is dependent on inductance, duty cycle, supply voltage and frequency:
I
RIPPLE
= DC x (V
DD
-V
SW
) / (f x L) (A)
where
• f = switching frequency = 1MHz (14)
combining all terms, we can develop an expression which allows the maximum available load current to be
calculated:
I
AMP(max)
= (1–DC) x [I
SW(max)
–DC(V-V
SW
)] / 2fL (A) (15)
The equation shown to calculate maximum load current takes into account the losses in the inductor or turn-off
switching losses of the FET and diode.
DESIGN PARAMETERS V
SW
AND I
SW
The value of the FET "ON" voltage (referred to as V
SW
in Equation 9 thru Equation 12) is dependent on load
current. A good approximation can be obtained by multiplying the on resistance (R
DS(ON)
of the FET times the
average inductor current. The maximum peak switch current the device can deliver is dependent on duty cycle.
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