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Table 10-1. Design Parameters (continued)

REFERENCE

DESCRIPTION

SAMPLE VALUES

VOUT

Output voltage range VSEL = High

VOUT= 3.35 V if VIN ≤ 3.35 V, VOUT = VIN if VIN > 3.35 V

IOUT

Output current

1500mA

10.2.1.2 Detailed Design Parameters

10.2.1.2.1 Inductor Selection

A boost converter normally requires two main passive components for storing energy during the conversion, an

inductor and an output capacitor are required. It is advisable to select an inductor with a saturation current rating

higher than the possible peak current flowing through the power switches.

The inductor peak current varies as a function of the load, the input and output voltages and can be estimated

using Equation 8.

OUT

L(PEAK)

OUT

V x D

with D

2 x f x L

(1 D) x

(8)

Selecting an inductor with insufficient saturation performance can lead to excessive peak current in the

converter. This could eventually harm the device and reduce it's reliability.

When selecting the inductor, as well as the inductance, parameters of importance are: maximum current

rating, series resistance, and operating temperature. The inductor DC current rating should be greater than

the maximum input average current, refer to Equation 9 and the Section 9.4.4 section for more details.

OUT

L(DC)

OUT

x I

(9)

The TPS6128xD series of step-up converters have been optimized to operate with a effective inductance in the

range of 200 nH to 800 nH. Larger or smaller inductor values can be used to optimize the performance of the

device for specific operating conditions. For more details, see the Section 10.2.1.2.4 section.

In high-frequency converter applications, the efficiency is essentially affected by the inductor AC resistance (that

is, quality factor) and to a smaller extent by the inductor DCR value. To achieve high efficiency operation, care

should be taken in selecting inductors featuring a quality factor above 25 at the switching frequency. Increasing

the inductor value produces lower RMS currents, but degrades transient response. For a given physical inductor

size, increased inductance usually results in an inductor with lower saturation current.

The total losses of the coil consist of both the losses in the DC resistance, R(DC) , and the following frequency-

dependent components:

• The losses in the core material (magnetic hysteresis loss, especially at high switching frequencies)

• Additional losses in the conductor from the skin effect (current displacement at high frequencies)

• Magnetic field losses of the neighboring windings (proximity effect)

• Radiation losses

For good efficiency, the inductor DC resistance should be less than 30 mΩ. The following inductor series from

different suppliers have been used with the TPS6128xD converters.

Table 10-2. List of Inductors

SERIES

DIMENSIONS (in mm)

DC INPUT CURRENT LIMIT SETTING

DFE252010C

2.5 x 2.0 x 1.0 max. height

≤3000 mA

DFE252012C

2.5 x 2.0 x 1.2 max. height

≤3500 mA

DFR252010C

2.5 x 2.0 x 1.0 max. height

≤3000 mA

DFE252012C

2.5 x 2.0 x 1.2 max. height

≤3500 mA

DFE252012P

2.5 x 2.0 x 1.2 max. height

≤3500 mA

DFE201610C

2.0 x 1.6 x 1.0 max. height

≤2000 mA

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TPS61280D, TPS61281D, TPS61282D,, TPS61280E

SLVSEA0B – JANUARY 2018 – REVISED JUNE 2023

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