MP3336 – DUAL-CHANNEL, FLASH, LED DRIVER WITH I

MP3336 Rev.1.01

www.MonolithicPower.com

25

5/16/2017

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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

for their low ESR and small temperature

coefficients. A capacitor with a higher value can

help reduce input voltage ripple and noise. For

most applications, a 10μF 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. An inductor with a larger value

results in less ripple current, a lower peak

inductor current, and reduced stress on the

internal N-channel MOSFET, but also has a

larger physical size, higher series resistance, and

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

with high efficiency and good EMI performance.

Calculate the required inductance value using

Equation (2) and Equation (3):

2

OUT

SW

LOAD

η V

D (1D)

L

2

f

I



 





(2)

IN

OUT

V

D1

V



(3)

the LED load current, and η is the efficiency.

The switching current is used for peak-current

mode control. To avoid hitting the current limit,

the worst-case inductor peak current should be

applications, 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 for their low

ESR characteristics. Ensure that the ceramic

capacitance is dependent on the voltage rating.

The DC bias voltage and the value can lose as

much as 50% of their capacitance at the rated

voltage rating. Ensure that enough of a voltage

rating margin is left when selecting the

component. A capacitance that is too low can

cause loop instability. For most applications, a

10μF ceramic capacitor is sufficient.

PCB Layout Guidelines

Efficient PBC layout is critical for stable operation.

For best results, follow the guidelines below.

1. Place a ceramic capacitor close to VIN.

2. Use a wider copper wire for input, output, and

GND to improve thermal performance.

3. Put as many vias close to GND at the output

and input capacitors as possible to improve

thermal performance.