Datasheet

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TPS65135
SLVS704A –NOVEMBER 2011–REVISED NOVEMBER 2011 www.ti.com
Output-Current Mismatch
The device operates best when the current of the positive output is similar to the current of the negative output.
However the device is able to regulate an output-current mismatch between the outputs of up to 50% (See
Figure 4 for typically allowed currents, only 50% mismatch is specified). If the output-current mismatch becomes
much larger one of the outputs goes out of regulation and finally the IC shuts down. In case of zero load of one
output the other output can support up to 5mA. The IC automatically recovers when the mismatch is reduced.
The below formula is used to calculate the maximum supported current mismatch.
(6)
Input Capacitor Selection
The device typically requires a 10 µF ceramic input capacitor. Larger values can be used to lower the input
voltage ripple. Table 2 lists capacitors suitable for use on the TPS65135 input.
Table 2. Input Capacitor Selection
CAPACITOR COMPONENT SUPPLIER SIZE
10 µF / 6.3V Murata GRM188R60J106ME84D 0603
10 µF / 6.3 V Taiyo Yuden JMK107BJ106 0603
Inductor Selection/Efficiency/Line-Transient Response
The device is internally compensated and operates best with a 2.2 µH inductor. For this type of converter the
inductor selection is a key element in the design process because it has a big impact on several application
parameters. The inductor selection influences the converter efficiency a lot, also the line and load transient
response as well as the maximum output current. Because the inductor ripple current is fairly large in this type of
application, the inductor has a major impact on the overall converter efficiency. Having large inductor ripple
current causes the inductor core and magnetizing losses to become dominant. Due to this, an inductor with a
larger dc winding resistance can achieve higher converter efficiencies when having lower core and magnetizing
losses. The used inductance influences the line transient regulation, it influences the current range entering
continuous conduction mode (CCM). As discussed, the line transient performance decreases when entering
CCM. The larger the inductor value, the lower the load current when entering CCM. The formula to calculate the
current entering CCM is shown in Equation 3. The inductors listed in Table 3 achieve a good overall converter
efficiency while having a low device profile. The first two TOKO inductors achieve the highest efficiency (almoust
identical) followed by the LPS3008. The best compromize between efficiency and inductor size is given by the
XFL2006 inductor . The inductor saturation current should be 1A or higher, depending on the maximum output
current of the application it can also be lower. See Equation 5, where the converter switch current limit is
calculated. The converter switch current is equal to the peak inductor current.
Table 3. Inductor Selection
INDUCTOR VALUE COMPONENT SUPPLIER DIMENSIONS in mm I
sat
/ R
DC
2.2 µH TOKO DFE252010C 2.5 x 2 x 1 1.9 A / 130 mΩ
2.2 µH TOKO DFE252012C 2.5 x 2 x 1.2 2.2 A / 90 mΩ
2.2 µH Coilcraft XFL2006-222 2 × 1.9 × 0.6 0.8 A / 278 mΩ
2.2 µH Coilcraft LPS3008-222 3 × 3 × 0.8 1.1 A / 175 mΩ
2.2 µH Samsung CIG2MW2R2NNE 2 × 1.6 × 1 1.2 A / 110 mΩ
2.2 µH TOKO FDSE0312-2R2 3.3 × 3.3 × 1.2 1.2 A / 160 mΩ
2.2 µH ABCO LPF3010T-2R2 2.8 × 2.8 × 1 1.0 A / 100 mΩ
2.2 µH Maruwa CXFU0208-2R2 2.65 × 2.65 × 0.8 0.85 A / 185 mΩ
12 Copyright © 2011, Texas Instruments Incorporated
Product Folder Links: TPS65135