Datasheet

Table Of Contents

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Component Selection

6 Component Selection

Before changing the default components refer to LM22671/LM22671Q 42V, 500mA SIMPLE SWITCHER

Step-Down Voltage Regulator with Features (SNVS589) for information regarding component selection.

The WEBENCH

designer online circuit simulation tool is also available on the TI website.

The output voltage is adjustable with resistors R1 and R2 shown in Figure 1. Any changes to these

evaluation board feedback resistors may require changes to the inductor and output capacitor values. It is

especially important to change the output capacitor, C4, if the output voltages are adjusted higher than 5V.

The Schottky diode, D1, has a voltage rating of 60V to allow for a 42V maximum input voltage. If the input

voltage is below 38V, a 40V Schottky diode may be used with a lower forward voltage to improve

efficiency. The input capacitor, C2, is not always required. This capacitor is placed on the evaluation board

to make the application robust and minimize input voltage ringing if power is suddenly applied. Capacitor

C2 also helps stabilize the transfer function of the converter loop. The input capacitor C1 provides the

main contribution to the switch current. Both capacitors are selected with appropriate values intended only

for the evaluation of the LM22671. For production designs, the impedance of the power source as well as

the ripple current rating of the selected input capacitors need to be taken into consideration and modified

accordingly. See the LM22671 datasheet (SNVS589) for more information.

Output capacitor C5 is not populated but space is provided to add a second output capacitor. This second

output capacitor may be used to further reduce output voltage ripple.

7 Bill of Materials

Table 1. LM22671EVAL Bill of Materials

Ref # Value Supplier Part Number

C1 2.2 uF 50V ceramic TDK C3225X7R1H225K

C2 22 µF 63V electrolytic Panasonic EEEFK1J220XP

C3 10 nF 50V ceramic TDK C1608X7R1H103K

C4 22 µF 6.3V ceramic TDK C2012X5R0J226M

C5 Not populated -

C6 1 µF 10V ceramic TDK C1608Y5V1A105Z

D1 60V 1A CMSH1-60 Central Semiconductor CMSH1-60

L1 39 µH 1.11A WE-PD M Wurth 7447779139

Coilcraft MSS7341-393MLD

R1 976Ω 1% - CRCW0603976RFKEA

R2 1.54 kΩ 1% - CRCW06031K54FKEA

R3 Not populated -

U1 Texas Instruments LM22671

SNVA368D–September 2008–Revised April 2013 AN-1895 LM22671 Evaluation Board

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