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CIN(RMS)

= 3A

0.5 x 0.5 = 1.5A

D =

OUT

CIN(RMS)

= I

OUT

D(1 - D)

Bill of Materials (BOM)

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5 Bill of Materials (BOM)

The Bill of Materials is shown in Table 2, including the manufacturer and part number.

Table 2. Bill of Materials (BOM)

Qty Designator Part Number Description Value

1 C1 GRM32ER61E226KE15 CAPACITOR, 1210 X5R CER, MURATA 22 µF, 25V

2 C2, C3 GRM21BR61E475KA12L CAPACITOR, 0805 X5R CER, MURATA 4.7 µF, 25V

1 C5 GRM188R71A105KA61D CAPACITOR, 0603 X7R CER, MURATA 1 µF, 10V

2 C4, C6 C1608X7R1H104K CAPACITOR, 0603 X7R CER, TDK 0.1 µF, 50V

1 C7 C1608C0G1H100J CAPACITOR, 0603 COG CER, TDK 10 pF, 50V

1 C8 C1608C0G1H821J CAPACITOR, 0603 COG CER, TDK 820 pF, 50V

1 C9 6TPB150MAZB CAPACITOR, POSCAP B, SANYO 150 µF, 6.3V

1 D1 CMMSH1-40-NST DIODE, SCHOTTKY, CENTRAL SEMI 1A, 40V

1 L1 IHLP4040DZER4R7M11 INDUCTOR, VISHAY 4.7 µH, 7.6A

2 R1, R6 CRCW06031002F RESISTOR, 0603, VISHAY 10 kΩ

2 R7, R8 CRCW06034992F RESISTOR, 0603, VISHAY 49.9 kΩ

0 R2, R3 OPEN - -

1 R4 CRCW0603348RF RESISTOR, 0603, VISHAY 348Ω

1 R5 CRCW06033092F RESISTOR, 0603, VISHAY 30.9 kΩ

1 U1 LM20343 SWITCHING REGULATOR, Texas

Instruments

4 J1 - J4 160-1026-02-01-00 TURRET TERMINAL, CAMBION TERMINAL,

TURRET

3 J6, J7, J9 5002 TERMINAL, SINGLE PIN, KEYSTONE TESTPOINT, LOOP

1 J5 5000 TERMINAL, SINGLE PIN, KEYSTONE TESTPOINT, LOOP

1 J8 5001 TERMINAL, SINGLE PIN, KEYSTONE TESTPOINT, LOOP

1 TP1 131503100 TEKTRONIX SCOPE PROBE TESTPOINT PROBE

TESTPOINT

6 Component Selection

This section provides a walk-through of the design process of the LM20343 evaluation board. Unless

otherwise indicated, all equations assume units of amps (A) for current, farads (F) for capacitance, henries

(H) for inductance, and volts (V) for voltages.

6.1 Input Capacitors: C1, C2, C3

The required RMS current rating of the input capacitor for a buck regulator can be estimated by

Equation 1:

(1)

The variable D refers to the duty cycle, and can be approximated by:

(2)

From this equation, it follows that the maximum I

CIN(RMS)

requirement will occur at a full 3A load current with

the system operating at 50% duty cycle. Under this condition, the maximum I

CIN(RMS)

is given by:

(3)

Ceramic capacitors feature a very large I

RMS

rating in a small footprint, making a ceramic capacitor ideal

for this application. A two 4.7 µF, X5R, 25V ceramic capacitor(C2, C3) from Murata are used to provide

the necessary input capacitance for the evaluation board. An additional 22uF, X5R, 25V capacitor is used

to provide additional input capacitance to counter cabling inductance to the input.

AN-1792 LM20343 Evaluation Board SNVA326B–May 2008–Revised May 2013

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