Datasheet

www.ti.com
DESIGN PROCEDURE
Inductor Selection for the Main and the Core Converter
I
L
 V
O

1–
V
O
V
I
L  ƒ
(3)
I
L(max)
 I
O(max)

I
L
2
(4)
Output Capacitor Selection
TPS65013
SLVS517A – AUGUST 2004 – REVISED JANUARY 2005
The main and the core converters in the TPS65013 typically use a 6.2-µH and a 10-µH output inductor,
respectively. Larger or smaller inductor values can be used to optimize the performance of the device for specific
operation conditions. The selected inductor has to be rated for its dc resistance and saturation current. The dc
resistance of the inductance directly influences the efficiency of the converter. Therefore, an inductor with lowest
dc resistance is selected for highest efficiency.
Equation 3 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 3 . This is needed
because during heavy load transient, the inductor current rises above the value calculated under Equation 3 .
with:
• f = Switching frequency (1.25 MHz typical)
• L = Inductor value
• ∆ I
L
= Peak-to-peak inductor ripple current
• I
Lmax
= Maximum inductor current
The highest inductor current occurs at maximum V
I
.
Open core inductors have a soft saturation characteristic, and they can usually 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
TPS65013 (2 A for the main converter and 0.8 A for the core converter). Keep in mind that the core material from
inductor to inductor differs and has an impact on the efficiency especially at high switching frequencies.
Refer to Table 4 and the typical applications for possible inductors
Table 4. Tested Inductors
DEVICE INDUCTOR VALUE DIMENSIONS COMPONENT SUPPLIER
10 µH 6,0 mm × 6,0 mm × 2,0 mm Sumida CDRH5D18-100
Core converter
10 µH 5,0 mm × 5,0 mm × 3,0 mm Sumida CDRH4D28-100
4.7 µH 5,5 mm × 6,6 mm x 1,0 mm Coilcraft LPO1704-472M
4.7 µH 5,0 mm × 5,0 mm × 3,0 mm Sumida CDRH4D28C-4.7
4.7 µH 5,2 mm × 5,2 mm × 2,5 mm Coiltronics SD25-4R7
Main converter
5.3 µH 5,7 mm × 5,7 mm × 3,0 mm Sumida CDRH5D28-5R3
6.2 µH 5,7 mm × 5,7 mm × 3,0 mm Sumida CDRH5D28-6R2
6.0 µH 7,0 mm × 7,0 mm × 3,0 mm Sumida CDRH6D28-6R0
The advanced fast response voltage mode control scheme of the inductive converters implemented in the
TPS65013 allow the use of small ceramic capacitors with a typical value of 22 µF for the main converter and 10
µF for the core converter without having large output voltage under and overshoots during heavy load transients.
Ceramic capacitors having low ESR values have the lowest output voltage ripple and are recommended. If
required, tantalum capacitors with an ESR < 100 Ω may be used as well.
Refer to Table 5 for recommended components.
49