Datasheet

I
LOAD
(max) = (1 - DC) x (I
SW
(max) - DC (V
IN
- V
SW
))
2fL
0 20 40 60 80 100
0
200
400
600
800
1000
1200
1400
1600
SWITCH CURRENT LIMIT (mA)
DUTY CYCLE (%) = [1 - EFF*(VIN/VOUT))]
V
IN
= 5V
V
IN
= 3.3V
V
IN
= 2.7V
LMR64010
SNVS736B –SEPTEMBER 2011–REVISED APRIL 2013 www.ti.com
MAXIMUM SWITCH CURRENT
The maximum FET swtch current available before the current limiter cuts in is dependent on duty cycle of the
application. This is illustrated in the graphs below which show both the typical and specified values of switch
current as a function of effective (actual) duty cycle:
Figure 20. Switch Current Limit vs Duty Cycle
CALCULATING LOAD CURRENT
As shown in the figure which depicts inductor current, the load current is related to the average inductor current
by the relation:
I
LOAD
= I
IND
(AVG) x (1 - DC)
where
• "DC" is the duty cycle of the application. (7)
I
SW
= I
IND
(AVG) + ½ (I
RIPPLE
) (8)
Inductor ripple current is dependent on inductance, duty cycle, input voltage and frequency:
I
RIPPLE
= DC x (V
IN
-V
SW
) / (f x L) (9)
combining all terms, we can develop an expression which allows the maximum available load current to be
calculated:
(10)
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