IN

L

SW

V

D

I

L

f

´

D

=

´

UP

OUT

FB

DOWN

R

V

V

(1

)

R

=

´

+

18

TPS61372

SLVSEE7 – JUNE 2018

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Copyright © 2018, Texas Instruments Incorporated

Typical Application (continued)

9.2.1 Design Requirements

For this design example, use as the design parameters.

Table 2. Design Parameters

PARAMETER

VALUE

Input voltage range

3 V to 5 V

Output voltage

12 V

Output ripple voltage

± 3%

Output current

0.4 A

Operating frequency

1.5 MHz

9.2.2 Detailed Design Procedure

9.2.3 Setting the Output Voltage

The output voltage of the TPS61372 is externally adjustable using a resistor divider network. The relationship

between the output voltage and the resistor divider is given by Equation 16.

where

•

•

•

(16)

MΩ + 909 kΩ) , resulting in an output voltage of 12 V.

quiescent current for achieving higher efficiency at the light load currents.

9.2.3.1 Selecting the Inductor

A boost converter normally requires two main passive components for storing the energy during the power

conversion: an inductor and an output capacitor. The inductor affects the steady state efficiency ( including the

ripple and efficiency ) as well as the transient behavior and loop stability, which makes the inductor to be the

most critical component in application.

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

•

The maximum current rating (RMS and peak current should be considered),

•

The series resistance,

•

Operating temperature

Choosing the inductor ripple current with the low ripple percentage of the average inductor current results in a

larger inductance value, maximizes the converter’s potential output current and minimizes EMI. The larger ripple

results in a smaller inductance value, and a physically smaller inductor, improves transient response but results

in potentially higher EMI.

The rule of thumb to choose the inductor is that to make the inductor ripple current (ΔIL) is a certain percentage

(Ripple % = 20 – 30 %) of the average current. The inductance can be calculated by Equation 17, Equation 18,

and Equation 19:

(17)