MP9162A – 2A, 6V, 1.5MHz, SYNCHRONOUS, STEP-DOWN CONVERTER

MP9162A Rev. 1.01

www.MonolihicPower.com

12

7/5/2016

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Selecting the Output Capacitor

The output capacitor (C2) is required to

maintain the DC output voltage. Low ESR

ceramic capacitors are recommended to keep

the output voltage ripple low. The output

voltage ripple can be estimated by Equation (8):

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.

When using ceramic capacitors, the impedance

at the switching frequency is dominated by the

capacitance, which mainly causes output

voltage ripples. For simplification, the output

voltage ripple can be estimated with Equation

(9):

OUT

OUT

OUT

2

IN

S1

VV

ΔV1

V

8f

L

C2



 



 



(9)

When using tantalum or electrolytic capacitors,

the ESR dominates the impedance at the

switching frequency. For simplification, the

output ripple can be approximated with

Equation (10):

OUT

OUT

OUT

ESR

IN

S1

VV

ΔV1

R

fL

V



 









(10)

The characteristics of the output capacitor

affect the stability of the regulation system.

PCB Layout Guidelines

Efficient PCB layout is critical for stable

operation. A poor layout design can result in

poor line or load regulation and stability issues.

For best results, refer to Figure 3 and follow the

guidelines below.

1. Place the high-current paths (GND, VIN,

and SW) as close to the device as possible

with short, direct, and wide traces.

2. Place the input capacitor as close to VIN

and GND as possible.

3. Place the external feedback resistors next

to FB.

4. Keep the switching node (SW) short and

away from the feedback network.

EN

GND

OUT

SW

VIN

1

2

3

4

8

7

6

5

PG

R1

C2

R2

C1

Figure 3: PCB Layout Recommendation

Design Example

Table 2 is a design example following the

application guidelines for the specifications

below:

Table 2: Design Example

5V

1.2V

1500kHz

The detailed application schematic is shown in

Figure 4. The typical performance and circuit

waveforms

are

shown

in

the

Typical

Performance Characteristics section on page 4.

For more device applications, please refer to

the related evaluation board datasheets.