MP3367

– 6-CHANNEL BOOST WLED DRIVER WITH HIGH DIM RATIO AND I2C

MP3367 Rev. 1.0

www.MonolithicPower.com

23

6/17/2019

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© 2019 MPS. All Rights Reserved.

APPLICATION INFORMATION

LED Current Setting

The LED current amplitude is set by an external

resistor connected from ISET to GND. The LED

current amplitude setting is determined with

Equation (4):

ISET

1245

ILED(mA)

R

(k )





(4)

Where RISET = 24.9kΩ, and the LED current is

50mA.

Switching Frequency

The switching frequency can be programmed

with a resistor, I2C interface, or external clock. To

program the frequency using an external resistor

on FREQ/SYNC, the switching frequency follows

Equation (5):





SW

OSC

22000

f (kHz)

R

(k )

(5)

For ROSC = 44.2kΩ, the switching frequency is set

to 500kHz.

Synchronize the switching frequency with an

external clock to improve EMI, efficiency, and

thermal performance.

If setting the switching frequency bit (fSW1:0), 00:

200kHz; 01: 400kHz; 10: 1MHz; 11: 2.2MHz.

Float FREQ if the fSW1:0 bit is used.

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. Use ceramic

capacitors with X5R or X7R dielectrics for their

low ESR and small temperature coefficients. For

most applications, a 10

μF ceramic capacitor is

sufficient.

Selecting the Inductor

The MP3367 requires an inductor to supply a

higher output voltage while being driven by the

input voltage. A higher value inductor results in

less ripple current, lower peak inductor current,

and less stress on the internal N-channel

MOSFET. However, it also has a larger physical

size,

higher

series

resistance,

and

lower

saturation current.

Choose an inductor that does not saturate under

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 (6) and Equation (7):





 





2

OUT

SW

LOAD

η V

D (1 D)

L

2

f

I

(6)



IN

OUT

V

D1

V

(7)

Where VIN and VOUT are the input and output

voltages, fSW is the switching frequency, ILOAD is

the LED load current, and η is the efficiency.

With the given inductor value, the inductor DC

current rating is at least 40% greater than the

maximum input peak inductor current for most

applications. The

inductor

’s DC resistance

should be as small as possible for higher

efficiency.

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. For most applications,

a 10

μF ceramic capacitor is sufficient.