Datasheet
VIN 2.5 V – 6 V
TPS62421
10 Fm
VIN
EN_1
EN_2
MODE/
DATA
GND
DEF_1
SW2
SW1
ADJ2
FB 1
2.2 Hm
2.2 Hm
22 Fm
22 Fm
V = 1.2V / 1.8V
600 mA
OUT1
V = 1.8 V
1000 mA
OUT2
1.2V
1.8V
DI
L
+ Vout
1 *
Vout
Vin
L ƒ
I
Lmax
+ I
outmax
)
DI
L
2
TPS62420, TPS62421
SLVS676C –JUNE 2006–REVISED JUNE 2010
www.ti.com
Figure 35. Typical Application Circuit TPS62421
OUTPUT FILTER DESIGN (INDUCTOR AND OUTPUT CAPACITOR)
The device is optimized to operate with inductors of 2.2mH to 4.7mH and output capacitors of 10mF to 22mF.
For operation with a 2.2mH inductor, a 22mF capacitor is suggested.
Inductor Selection
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 7. This is
recommended because during heavy load transient the inductor current will rise above the calculated value.
(6)
(7)
With:
f = Switching Frequency (2.25MHz typical)
L = Inductor Value
ΔI
L
= Peak to Peak inductor ripple current
I
Lmax
= Maximum Inductor current
The highest inductor current will occur at maximum Vin.
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
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 7 and the typical applications for possible inductors.
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