MP3332

MP3332 Rev. 1.0

www.MonolithicPower.com

25

5/1/2018

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© 2018 MPS. All Rights Reserved.

APPLICATION INFORMATION

Selecting the Input Capacitor

The input capacitor reduces the surge current

drawn from the input supply and the switching

noise from the device. The input capacitor

impedance at the switching frequency should be

less than the input source impedance to prevent

the

high-frequency

switching

current

from

passing through to the input. Ceramic capacitors

with X5R or X7R dielectrics are recommended

because of their low ESR and small temperature

coefficients. A capacitor with a higher value is

recommended to reduce input voltage ripple and

noise. For most applications, a 10

μF ceramic

capacitor is sufficient.

Selecting the Inductor

The converter requires an inductor to supply a

higher output voltage while being driven by the

input voltage. A larger value inductor generates

less ripple current, resulting in a lower peak

inductor current and less stress on the internal N-

channel MOSFET. However, the larger value

inductor has a larger physical size, a higher

series resistance, and a lower saturation current.

Choose an inductor that does not saturate under

the

worst-case

load

conditions.

Select

the

minimum inductor value to ensure that the boost

converter works in continuous conduction mode

(CCM) with high efficiency and good EMI

performance.

The required inductance value can be calculated

with Equation (1) and Equation (2):

2

OUT

SW

LOAD

η V

D (1 D)

L

2

f

I





 





(1)

OUT

IN

V

V

1

D





(2)

the LED load current, and η is the efficiency.

The switching current is used for the peak current

mode control. To avoid hitting the current limit,

the worst-case inductor peak current should be

applications, a 0.47µH~2µH inductor is sufficient.

Selecting the Output Capacitor

The output capacitor keeps the output voltage

ripple small and ensures feedback loop stability.

The output capacitor impedance must be low at

the switching frequency. Ceramic capacitors with

X7R dielectrics are recommended because of

their low ESR characteristics. Care must be

taken to ensure that the ceramic capacitance is

dependent on the voltage rating since the DC

bias voltage and the value can lose as much as

50% of its capacitance at its rated voltage rating.

Please leave enough of a voltage rating margin

when selecting the component, as a capacitance

that is too low causes loop instability. For most

applications,

a

10

μF ceramic capacitor is

sufficient.

PCB Layout Guidelines

Efficient PCB layout is critical for stable operation.

For best results, refer to Figure 17 and follow the

guidelines below.

1. Place the input capacitor as close to VIN as

possible.

2. Use wider copper traces for the input, output,

and GND connecting wire to improve thermal

performance.

3. Place the GND via as close to the output and

input

capacitor

as

possible

to

improve

thermal performance.

LED1 OUT

SW

LED2 OUT

SW

TOR

TX

STR

PGND

PNGD

VSS

NTC

SDA

SCL

VIN

IN

OUT

GND

LED1

LED2

Figure 17: Recommended Layout