Datasheet
I
SAT
> IL
PEAK
IL
PEAK
= I
OUTMAX
+
I
RIPPLE
2
I
RIPPLE
=
(V
IN
±
V
OUT
)
L x F
S
D x
D =
V
OUT
V
IN
x EFF
I
L(MAX)
= I
LOAD(MAX)
+ û I
RIPPLE
(A typ.),
, F
S
= 2 MHz, L = 2.2 µH
V
OUT
V
IN
D =
~
~
I
LOAD(MAX)
+
D x (V
IN
- V
OUT
)
2 x 2.2 x 2.0
= I
LOAD(MAX)
+
D x (V
IN
- V
OUT
)
2 x L x F
S
LM10506
SNVS729E –SEPTEMBER 2011–REVISED MARCH 2013
www.ti.com
External Components Selection
All three switchers require an input capacitor and an output inductor-capacitor filter. These components are
critical to the performance of the device. All three switchers are internally compensated and do not require
external components to achieve stable operation. The output voltages of the bucks can be programmed through
the SPI pins.
OUTPUT INDUCTORS & CAPACITORS SELECTION
There are several design considerations related to the selection of output inductors and capacitors:
• Load transient response
• Stability
• Efficiency
• Output ripple voltage
• Over current ruggedness
The device has been optimized for use with nominal LC values as shown in the Typical Application Circuit.
INDUCTOR SELECTION
The recommended inductor values are shown in Typical Application Diagram. It is important to ensure the
inductor core does not saturate during any foreseeable operational situation. The inductor should be rated to
handle the peak load current plus the ripple current:
Care should be taken when reviewing the different saturation current ratings that are specified by different
manufacturers. Saturation current ratings are typically specified at 25°C, so ratings at maximum ambient
temperature of the application should be requested from the manufacturer.
(1)
There are two methods to choose the inductor saturation current rating:
Recommended Method for Inductor Selection:
The best way to ensure the inductor does not saturate is to choose an inductor that has saturation current rating
greater than the maximum device current limit, as specified in the Electrical Characteristics tables. In this case
the device will prevent inductor saturation by going into current limit before the saturation level is reached.
Alternate Method for Inductor Selection:
If the recommended approach cannot be used care must be taken to ensure that the saturation current is greater
than the peak inductor current:
• I
SAT
: Inductor saturation current at operating temperature
• I
LPEAK
: Peak inductor current during worst case conditions
• I
OUTMAX
: Maximum average inductor current
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