Datasheet

OUTPUT FILTER DESIGN (INDUCTOR AND OUTPUT CAPACITOR)
Inductor Selection
DI
L
+ Vout
1 *
Vout
Vin
L ƒ
I
Lmax
+ I
out
max )
DI
L
2
(6)
TPS65053
TPS650531
TPS650532
www.ti.com ............................................................................................................................................. SLVS754C – MARCH 2007 – REVISED SEPTEMBER 2009
Table 1. Typical Resistor Values
OUTPUT VOLTAGE R1 R2 NOMINAL VOLTAGE TYPICAL CFF
3.3 V 680 k Ω 150 k Ω 3.32 V 47 pF
3.0 V 510 k Ω 130 k Ω 2.95 V 47 pF
2.85 V 560 k Ω 150 k Ω 2.84 V 47 pF
2.5 V 510 k Ω 160 k Ω 2.51 V 47 pF
1.8 V 300 k Ω 150 k Ω 1.80 V 47 pF
1.6 V 200 k Ω 120 k Ω 1.60 V 47 pF
1.5 V 300 k Ω 200 k Ω 1.50 V 47 pF
1.2 V 330 k Ω 330 k Ω 1.20 V 47 pF
The two converters operate typically with 2.2 µ H output inductor. Larger or smaller inductor values can be used to
optimize the performance of the device for specific operation conditions. For output voltages higher than 2.8V, an
inductor value of 3.3 µ H minimum should be selected, otherwise the inductor current will ramp down too fast
causing imprecise internal current measurement and therefore increased output voltage ripple under some
operating conditions in PFM mode.
The selected inductor has to be rated for its DC resistance and saturation current. The DC resistance of the
inductance will influence directly the efficiency of the converter. Therefore an inductor with lowest DC resistance
should be selected for highest efficiency.
Equation 6 calculates the maximum inductor current under static load conditions. The saturation current of the
inductor should be rated higher than the maximum inductor current as calculated with Equation 6 . This is
recommended because during heavy load transient the inductor current will rise above the calculated value.
with:
f = Switching Frequency (2.25-MHz typical)
L = Inductor Value
Δ I
L
= Peak-to-peak inductor ripple current
I
Lmax
= Maximum Inductor current
The highest inductor current occurs at maximum Vin. Open core inductors have a soft saturation characteristic,
and they can normally handle higher inductor currents versus a comparable shielded inductor.
A more conservative approach is to select the inductor current rating just for the maximum switch current of the
corresponding converter. It must be considered, that the core material from inductor to inductor differs and will
have an impact on the efficiency especially at high switching frequencies. Refer to Table 2 and the typical
applications for possible inductors.
Table 2. Tested Inductors
Inductor Type Inductor Value Supplier
LPS3010 2.2 µ H Coilcraft
LPS3015 3.3 µ H Coilcraft
LPS4012 2.2 µ H Coilcraft
VLF4012 2.2 µ H TDK
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