AN4501 datasheet(7/48 Pages) STMICROELECTRONICS

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AN4501

Guideline for the selection of external components

This section provides a guideline for the dimensioning power components of the boost

converter. The guideline takes into account the impact of the wide range of the input voltage

on the component stress.

The reader can find the list of abbreviations in Table 4.

2.1

Guideline

Step 1: Calculate the extreme duty cycles and minimum converter on-time

•

Calculate the minimum and maximum duty cycles DMIN and DMAX

•

Verify that the operation is compatible with the converter minimum on-time (tON,MIN)

•

Verify that DMAX does not exceed the converter duty cycle limitation

Step 2: Selection of the inductor

•

Calculate the maximum inductor DC current IL,MAX

•

Calculate the minimum inductance to comply with the requested ratio inductance

current ripple to DC current at the minimum input voltage (IL,PP@VINMIN / IL,MAX)

•

Select the standardized inductor value

•

Recalculate IL,PP@VINMIN with the selected standardized inductance value

Step 3: Selection of the freewheel diode

•

Calculate the minimum breakdown voltage and the required current capability

Step 4: Selection of the output capacitor

•

Choose a voltage capability, which is higher than the overvoltage protection

•

Calculate the required output capacitance fulfilling the maximum output current ripple

Step 4: Selection of the input capacitor

•

Calculate the minimum capacitance fulfilling the required input voltage ripple

Step 5: Selection of the switching MOSFET

•

Choose a MOSFET and determine the corresponding switching losses (at VIN,MIN)

•

Calculate the MOSFET RMS current

•

Make an iterative calculation of the total power dissipation (at VIN,MIN)

•

Verify that the maximum junction temperature does not exceed the MOSFET maximum

rating.

2.2

Application example

Table 1. Example of application conditions and requirements

Parameter

Value

Comments

VIN

6 V to 18 V

Operating input voltage

IOUT

1 A

Output current

VOUT

2 6V

VOUT ~ LED voltage

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