TPS62420_15 Datasheet, PDF (22/38 Pages) Texas Instruments – TPS6242x 2.25-MHz 600-mA and 1000-mA Dual Step-Down Converter in Small 3-mm × 3-mm VSON Package

TPS62420, TPS62421
SLVS676D – JUNE 2006 – REVISED JULY 2015
9.2 Typical Applications
9.2.1 Typical Application Circuit 1.5-V and 2.85-V Adjustable Outputs
TPS62420
VIN 3.3 V – 6 V
VIN
C_IN
10 mF
EN_1
FB 1
SW1
DEF_1
L1
2.2 mH
R11
270 kW
R12
180 kW
V_OUT1 = 1.5 V
up to 600 mA
C_OUT1 = 22 mF
EN_2
MODE/
DATA
SW2
ADJ2
GND
L2
3.3 mH
R21 Cff2
825 kW 33 pF
R22
220 kW
V_OUT2 = 2.85 V
up to 1000 mA
C_OUT2 = 22 mF
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Figure 14. Typical Application Circuit 1.5-V and 2.85-V Adjustable Outputs
9.2.1.1 Design Requirements
The step-down converter design can be adapted to different output voltage and load current needs by choosing
external components appropriate. The following design procedure is adequate for whole V_IN, V_OUT and load
current range of TPS62420.
9.2.1.2 Detailed Design Procedure
9.2.1.2.1 Output Filter Design (Inductor and Output Capacitor)
The device is optimized to operate with inductors of 2.2 μH to 4.7 μH and output capacitors of 10 μF to 22 μF.
For operation with a 2.2-μH inductor, a 22-μF capacitor is suggested.
9.2.1.2.1.1 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.
DI_L + Vout
1
*
Vout
Vin
Lƒ
(6)
I_Lmax
+
I_outmax
)
DI_L
2
where
• f = Switching frequency (2.25 MHz typical)
• L = Inductor value
• ΔI_L= Peak-to-peak inductor ripple current
• I_Lmax = Maximum inductor current
(7)
22
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