MP3362

– SINGLE-STRING, 3V MINIMUM Vin, 36V BOOST LED DRIVER

MP3362 Rev. 1.1

www.MonolithicPower.com

13

2/22/2023

MPS Proprietary Information. Patent Protected Unauthorized Photocopy and Duplication Prohibited.

© 2023 MPS. All Rights Reserved.

APPLICATION INFORMATION

LED Current Setting

The LED current is set by the feedback resistor

(RFB). 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 )

=



(3)

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

OSC/SYNC pin can also synchronize fSW.

Selecting the Inductor

The minimum inductance to make the circuit work

in continuous conduction mode (CCM) can be

calculated with Equation (4):

IN

O

IN

OL

sw

V

(V

V )

L=

V

I

f

−

  

(4)

Where

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

If the inductance is below this minimum value, the

circuit works in discontinuous conduction mode

(DCM).

Design

∆IL to be between 30% and 60% of the

average inductor current, estimated with Equation

(5):

O

LED

L_AVG

IN

VI

I=

V



(5)

Ensure that the saturated inductor current exceeds

the inductor peak current, estimated with Equation

(6):

L_PK

L_AVG

L

1

I

=I

+

I

2



(6)

Over-Voltage Protection (OVP) Setting

Set the over-voltage-protection (OVP) voltage

threshold above 10% to 20% of the output voltage.

The OVP voltage can be set with a voltage divider

(see the Typical Application Circuit section on

page 15). The threshold can be calculated with

Equation (7):

OVP1

OVP2

OVP

OVP2

RR

V

(V)=

1.2(V)

R

+



(7)

Selecting the Diode

Choose a diode with voltage rating greater than

the OVP point, and leave 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 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 (8):

L

IN

IN

sw

I

C

8

V

f





 



(8)

Selecting the Output Capacitor

Select an output capacitor that limits the output

voltage ripple (

∆VO) below 1% to 5% of its DC

value, and ensures feedback loop stability. The

capacitance can be estimated with Equation (9):

LED

O

IN

OUT

O

sw

O

I

(V

V )

C

V

f

V

−











(9)