MP2174C

– 5.5V, 4A, 1.1MHZ SYNCHRONOUS STEP-DOWN SWITCHER

MP2174C Rev. 1.0

www.MonolithicPower.com

14

8/7/2019

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Selecting the Output Capacitor

An output capacitor (C2) is required to maintain

the DC output voltage.

Low-ESR ceramic capacitors can be used with

the MP2174C to keep the output ripple low.

Generally, a 10

μF output ceramic capacitor is

sufficient. In higher output voltage conditions, a

22

μF capacitor may be needed for system

stability.

Using ceramic capacitors, the capacitance

dominates the impedance at the switching

frequency, and is the main cause of the output

voltage ripple. For simplification, the output

voltage ripple can be estimated with Equation

(8):





 





 



OUT

OUT

OUT

2

SW

1

IN

VV

ΔV1

8 f

L

C2

V

(8)

For tantalum or electrolytic capacitors, the ESR

dominates the impedance at the switching

frequency. For simplification, the output ripple

can be estimated with Equation (9):





 









OUT

OUT

OUT

ESR

IN

SW

1

VV

ΔV

1

R

f

L

V

(9)

The characteristics of the output capacitor also

affect the stability of the regulation system.

PCB Layout Guidelines

Efficient

PCB

layout

is

critical for

stable

operation. For best results, refer to Figure 3 and

follow the guidelines below:

1. Place the input decoupling capacitor as

close as possible to the IC pins, pin 1 and

pin 3 (an 0805 ceramic capacitor is used).

2. Ensure

the two

ends

of

the

ceramic

capacitor are connected directly to PVIN

(pin 1) and PGND (pin 3).

PG

EN

VIN

GND

VOUT

SW

R2

R1

L1

C1

SW

VIN

GND

Top Layer

Bottom Layer

Figure 3: Recommended PCB Layout