Datasheet

DI
L
+ Vout
1 *
Vout
Vin
L ƒ
I
Lmax
+ I
outmax
)
DI
L
2
TPS65020
SLVS607C –SEPTEMBER 2005– REVISED SEPTEMBER 2011 www.ti.com
LDO_CTRL. Register Address: 08h (read/write) Default Value: 23h
LDO_CTRL B7 B6 B5 B4 B3 B2 B1 B0
Bit name and
LDO2_2 LDO2_1 LDO2_0 LDO1_2 LDO1_1 LDO1_0
function
Default 0 1 0 0 1 1
Default value
UVLO UVLO UVLO UVLO UVLO UVLO
loaded by:
Read/Write R/W R/W R/W R/W R/W R/W
The LDO_CTRL registers can be used to set the output voltage of LDO1 and LDO2.
LDO1 OUTPUT LDO2 OUTPUT
LDO1_2 LDO1_1 LDO1_0 LDO2_2 LDO2_1 LDO2_0
VOLTAGE VOLTAGE
0 0 0 1 V 0 0 0 1 V
0 0 1 1.05 V 0 0 1 1.05 V
0 1 0 1.1 V 0 1 0 1.1 V
0 1 1 1.3 V 0 1 1 1.3 V
1 0 0 1.8 V 1 0 0 1.8 V
1 0 1 2.5 V 1 0 1 2.5 V
1 1 0 3 V 1 1 0 3 V
1 1 1 3.3 V 1 1 1 3.3 V
DESIGN PROCEDURE
Inductor Selection for the DC-DC Converters
Each of the converters in the TPS65020 typically use a 3.3 μH output inductor. Larger or smaller inductor values
are 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 influences directly the
efficiency of the converter. Therefore, an inductor with lowest dc resistance should be selected for highest
efficiency.
For a fast transient response, a 2.2-μH inductor in combination with a 22-μF output capacitor is recommended.
Equation 4 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 4. This is needed
because during heavy load transient the inductor current rises above the value calculated under Equation 4.
(4)
(5)
with:
f = Switching Frequency (1.5 MHz 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
TPS65020 (2 A for the VDCDC1 and VDCDC2 converters, and 1.3 A for the VDCDC3 converter). The core
material from inductor to inductor differs and has an impact on the efficiency especially at high switching
frequencies.
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