Datasheet

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Component Selection

5 Component Selection

Before changing the default components, refer to LM22670/LM22670Q 42V, 3A SIMPLE SWITCHER,

Step-Down Voltage Regulator with Features (SNVS584) 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. For improved heat dissipation, a Schottky diode in a D2PAK package may be selected for

higher 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 LM22670. 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 LM22670 datasheet (SNVS584) 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.

6 Bill of Materials

Table 1. LM22670EVAL Bill of Materials

Ref # Value Supplier Part Number

C1 6.8 µF 50V ceramic TDK C4532X7R1H685M

C2 22 µF 63V electrolytic Panasonic EEEFK1J220XP

C3 10 nF 50V ceramic TDK C1608X7R1H103K

C4 120 µF 6.3V 24mohm Nippon Chemi-Con APXE6R3ARA121ME61G

C5 Not populated -

C6 Not populated; not applicable for LM22670 -

D1 60V 5A CMSH5-60 Central Semiconductor CMSH5-60

L1 8.2 µH 6.25A WE-PD L Wurth 744771008

Coilcraft MSS1260-822MX

R1 976Ω 1% - CRCW0603976RFKEA

R2 1.54 kΩ 1% - CRCW06031K54FKEA

R3 Not populated -

U1 Texas Instruments LM22670

SNVA361D–September 2008–Revised April 2013 AN-1885 LM22670 Evaluation Board

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