Datasheet

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I
L
 V
O

1–
V
O
V
I
L  ƒ
(6)
I
L
max  I
O
max 
I
L
2
(7)
Output Capacitor Selection
I
RMSCout
 V
O

1–
V
O
V
I
L  ƒ

1
2  3

(8)
TPS62020
TPS62021
TPS62026
SLVS076C – JUNE 2003 – REVISED DECEMBER 2004
APPLICATION INFORMATION (continued)
inductor value, increase the output capacitor accordingly. See the application circuits in Figure 17 , Figure 18 , and
Figure 19 . 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 the lowest dc
resistance should be selected for highest efficiency. Formula Equation 7 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 formula Equation 7 . This is needed because during heavy load transient the
inductor current rises above the value calculated under Equation 7 .
with:
• 7 = Switching frequency (1.25 MHz typical)
• L = Inductor value
• ∆ I
L
= Peak-to-peak inductor ripple current
• I
L
max = 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 for
the maximum switch current of 1.3 A for the TPS6202x. Keep in mind that core material differs from inductor to
inductor, and this impacts efficiency, especially at high switching frequencies. Refer to Table 1 and the typical
applications and inductors selection.
Table 1. Inductor Selection
INDUCTOR VALUE DIMENSIONS COMPONENT SUPPLIER
10 µH 6,6 mm × 4,75 mm × 2,92 mm Coilcraft DO1608C-103
10 µH 5,0 mm × 5,0 mm × 3,0 mm Sumida CDRH4D28-100
3.3 µH 5,0 mm × 5,0 mm × 2,4 mm Sumida CDRH4D22 3R3
6.8 µH 5,8 mm × 7,4 mm × 1,5 mm Sumida CMD5D13 6R8
The advanced, fast-response voltage-mode control scheme of the TPS6202x allows the use of small ceramic
capacitors with a typical value of 10 µF and 22 µF 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 may be used as well. Refer to Table 2 for component
selection. If ceramic output capacitors are used, the capacitor RMS ripple current rating always meets the
application requirements. Just for completeness the RMS ripple current is calculated as:
At nominal load current the device operates in PWM mode and the overall output voltage ripple is the sum of the
voltage spike caused by the output capacitor ESR plus the voltage ripple caused by charging and discharging the
output capacitor:
14