MP3363

– SINGLE-STRING, 1.8V MINIMUM VIN, 36 VOUT BOOST LED DRIVER

MP3363 Rev. 1.0

MonolithicPower.com

11

9/28/2021

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© 2021 MPS. All Rights Reserved.

APPLICATION INFORMATION

LED Current (ILED) Setting

ILED is set by the LED current feedback resistor

(RFB). The value of RFB can be calculated with

Equation (2):



FB

LED

200mV

R

I

(2)

Switching Frequency Setting

The switching frequency (fSW) is set by an

external resistor (ROSC) at the OSC/SYNC pin.

fSW can be estimated with Equation (3):

SW

OSC

40000

f

(kHz)

R

(k

Ω)



(3)

A PWM signal (200kHz to 2.2MHz) on the

OSC/SYNC pin can also synchronize fSW.

Selecting the Inductor

The MP3363 requires an inductor to supply a

higher output voltage while being driven by the

input voltage. A larger-value inductor results in

less ripple current, lower peak inductor current,

and less stress on the internal N-channel

MOSFET. However, a larger-value inductor 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 (CCM) with high efficiency and excellent

EMI performance.

Calculate the required inductance value with

Equation (4):

2

OUT

SW

LOAD

η V

D (1 D)

L

2 f

I



  





(4)

Where VOUT is the output voltage, fSW is the

switching frequency, ILOAD is the LED load

current, η is the efficiency, and D can be

estimated with Equation (5):

IN

OUT

V

D=1-

V

(5)

Where VIN is the input voltage.

For a given inductor value, the inductor DC

current rating should be at least 40% higher

than the maximum input peak inductor current

for

most

applications. The inductor’s DC

resistance should be as small as possible for

higher efficiency.

Over-Voltage Protection (OVP) Setting

Generally, set the OVP voltage threshold to be

10% to 20% higher than VOUT. The OVP

threshold can be set with a voltage divider (see

the Typical Application section on page 1). The

OVP threshold can be calculated with Equation

(6):

OVP1

OVP2

OVP

OVP2

RR

V

(V)

1.2(V)

R





(6)

Selecting the Diode

Choose a diode with a voltage rating greater

than the OVP threshold, and leave about a 20%

margin.

The

current

rating

should

be

approximately two to three times greater than

the LED current.

Selecting the Input Capacitor

The input capacitor (CIN) reduces the surge

current drawn from the input supply and the

switching noise from the device. Ceramic

capacitors

with

X7R

dielectrics

are

recommended due to their low ESR and small

temperature coefficients.

Select a capacitor that limits the input voltage

ripple (

∆VIN) below 5% to 10% of its DC value.

The

capacitance

can

be

calculated

with

Equation (7):





 



L

IN

IN

SW

I

C

8

V

f

(7)

Where

∆IL is the peak-to-peak inductor current.

∆IL can be estimated with Equation (8):







IN

L

SW

VD

I

Lf

(8)

Selecting the Output Capacitor

Select an output capacitor (COUT) that limits the

output voltage ripple (

∆VOUT) below 1% to 5% of