MP2160 – 1.2A PEAK, 6V, 3.5MHz SYNCHRONOUS STEP-DOWN SWITCHER

MP2160 Rev. 1.03

www.MonolihicPower.com

11

7/5/2016

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Selecting the Output Capacitor

The output capacitor (C2) is required to

maintain the DC output voltage. Ceramic

capacitors

are

recommended.

Low

ESR

capacitors are preferred to keep the output

voltage ripple low. The output voltage ripple can

be estimated by:

OUT

OUT

OUT

ESR

S1

IN

S

VV

1

V1

R

fL

V

8 f

C2







 









 

 

equivalent series resistance (ESR) value of the

output capacitor.

Using ceramic capacitors, the impedance at the

switching frequency is dominated by the

capacitance. The output voltage ripple is mainly

caused by the capacitance. For simplification,

the output voltage ripple can be estimated by:

OUT

OUT

OUT

2

IN

S1

VV

ΔV1

V

8f

L

C2



 



 



In the case of tantalum or electrolytic capacitors,

the ESR dominates the impedance at the

switching frequency. For simplification, the

output ripple can be approximated to:

OUT

OUT

OUT

ESR

IN

S1

VV

ΔV1

R

fL

V



 









The characteristics of the output capacitor also

affect the stability of the regulation system.

PCB Layout

The high current paths (GND, VIN and SW)

should be placed very close to the device with

short, direct and wide traces. The input

capacitor needs to be as close as possible to

the VIN and GND pins. The external feedback

resistors should be placed next to the FB pin.

Keep the switching node SW short and away

from the feedback network.

EN

AGND

OUT

GND

SW

VIN

1

2

3

4

8

7

6

5

PG

C2

R2

C1

Design example

Below is a design example following the

application

guidelines

for

the

following

specifications:

Table 2: Design Example

5V

1.2V

frequency

3.5MHz

page 12 shows the detailed application

schematic, and is the basis for the typical

performance and circuit waveforms. For more

detailed device applications, please refer to the

related Evaluation Board Datasheets.