Datasheet

I
SAT
> IL
PEAK
IL
PEAK
= I
OUTMAX
+
I
RIPPLE
2
I
RIPPLE
=
(V
IN
± V
OUT
)
L x F
D x
D =
V
OUT
V
IN
x EFF
LM26484
www.ti.com SNVS573F –SEPTEMBER 2008–REVISED MARCH 2013
INDUCTOR SELECTION FOR SW1 AND SW2
A nominal inductor value of 0.5 µH is recommended. It is important to ensure the inductor core does not saturate
during any foreseeable operational situation.
Care should be taken when reviewing the different saturation current ratings that are specified by different
manufacturers. Saturation current ratings are typically specified at 25ºC, so ratings at maximum ambient
temperature of the application should be requested from the manufacturer.
There are two methods to choose the inductor saturation current rating:
Recommended method:
The best way to ensure the inductor does not saturate is to choose an inductor that has saturation current rating
greater than the maximum LM26484 current limit of 3.0A. In this case the device will prevent inductor saturation.
Alternate method:
If the recommended approach cannot be used, care must be taken to ensure that the saturation current is
greater than the peak inductor current:
where
• I
SAT
: Inductor saturation current at operating temperature
• I
LPEAK
: Peak inductor current during worst case conditions
• I
OUTMAX
: Maximum average inductor current
• I
RIPPLE
: Peak-to-Peak inductor current
• V
OUT
: Output voltage
• V
IN
: Input voltage
• L: Inductor value in Henries at I
OUTMAX
• F: Switching frequency, Hertz
• D: Estimated duty factor
• EFF: Estimated power supply efficiency
• (4)
I
SAT
may not be exceeded during any operation, including transients, startup, high temperature, worst case
conditions, etc.
Inductor Value Unit Description Notes
L1 and L2 0.5 µH SW1 and SW2 inductor D.C.R. 50 mΩ
SUGGESTED INDUCTORS AND THEIR SUPPLIERS
Output Voltage Range Vendor Part Number Value DCR (max)
V
OUT
≥ 2.0V Coilcraft LPS4012–222ML 2.2 µH 100 mΩ
V
OUT
< 2.0V Coilcraft LPS4414–501ML 0.5 µH 50 mΩ
OUTPUT CAPACITOR SELECTION FOR SW1 AND SW2
A ceramic output capacitor of 10 µF, 6.3V is recommended with an ESR of less than 500 mΩ.
Output ripple can be estimated from the vector sum of the reactive (Capacitor) voltage component and the real
(ESR) voltage component of the output capacitor.
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