TPS62400_101 Datasheet, PDF (31/44 Pages) Texas Instruments – 2.25MHz 400mA/600mA Dual Step-Down Converter In Small 3x3mm QFN Package

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TPS62403
VIN 2.5 V – 6 V
VIN
FB 1
10 m F
SW 1
2.2 µH
EN _1
EN _2
DEF _1
SW 2
3.3 µH
MODE/
DATA
ADJ 2
GND
TPS62400, TPS62401
TPS62402, TPS62403, TPS62404
SLVS681E – JUNE 2006 – REVISED APRIL 2010
Vout 1 : 1.575 V
400 mA
10 µF
Vout 2: 2.8 V
600 mA
10 µF
Figure 47. TPS62403 1.575V/2.8V Outputs
OUTPUT FILTER DESIGN (INDUCTOR AND OUTPUT CAPACITOR)
The converters are designed to operate with a minimum inductance of 1.75mH and minimum capacitance of 6mF.
The device is optimized to operate with inductors of 2.2mH to 4.7mH and output capacitors of 10mF to 22mF.
Inductor selection
The selected inductor has to be rated for its DC resistance and saturation current. The DC resistance of the
inductor 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 rises above the calculated value.
DI_L + Vout
1
*
Vout
Vin
Lƒ
(6)
I_Lmax
+
I_outmax
)
DI_L
2
(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 occurs 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. Take into consideration that the core material from inductor to inductor differs and this
difference has an impact on the efficiency.
Refer to Table 7 and the typical application circuit examples for possible inductors.
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