MP3383

– 4-STRING, MAX 80V VOUT, STEP-UP WLED CONTROLLER

MP3383 Rev. 1.0

MonolithicPower.com

17

5/2/2022

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

© 2022 MPS. All Rights Reserved.

The

maximum

duty

cycle

(DMAX) can be

calculated using Equation (8):

OUT

IN(MIN)

MAX

OUT

VV

D

V

−



(8)

The

MOSFET’s current rating should be 1.5

times greater than IRMS(MAX).

The

MOSFET’s

RDS(ON)

determines

the

conduction loss (PCOND), which can be calculated

using Equation (9):

2

COND

RMS

DS(ON)

P

= I

R

k



(9)

Where

k

is

the

MOSFET

’s temperature

coefficient.

The switching loss is related to QGD and QGS,

which determine the commutation time. QGS is

the charge between the threshold voltage and

the plateau voltage when a driver charges the

gate, which can be read in the VGS vs. QG chart

of the MOSFET datasheet. QGD is the charge

during

the

plateau

voltage.

These

two

parameters are required to estimate the turn-on

and

turn-off

losses

(PSW),

which

can

be

calculated using Equation (10):



=



 

+

−





 

−

GS

G

SW

DS

IN

SW

DR

TH

GD

G

DS

IN

SW

DR

PLT

QR

P

V

I

f

VV

QR

V

I

f

VV

(10)

Where VDR is the drive voltage, VTH is the

threshold voltage, VPLT is the plateau voltage,

VDS is the drain-to-source voltage, and RG is the

gate resistance.

RG is recommended to be between 10Ω and 20Ω.

Note that calculating the switching loss is the

most difficult part of loss estimation. Equation

(10) provides a simplified equation. For more

accurate estimates, the calculations become

significantly more complex.

The total gate charge (QG) is used to calculate

the gate drive loss (PDR). PDR can be calculated

using Equation (11):

SW

DR

G

DR

f

V

Q

P





=

(11)

Selecting the Output Capacitor

The output capacitor (COUT) keeps the VOUT ripple

small and ensures feedback loop stability. COUT

impedance must be low at fSW. Ceramic

capacitors

with

X7R

dielectrics

are

recommended for their low ESR characteristics.

A 4.7

μF ceramic capacitor in parallel with a 22μF

to 47

μF electrolytic capacitor is sufficient for

most applications.

Setting the Over-Voltage Protection (OVP)

Open-string protection is achieved by detecting

VOVP. In some cases, an LED string open fault

results in VFB always being 0V. The MP3383

continues boosting VOUT higher and higher. If

VOUT reaches the configured OVP threshold,

OVP is triggered.

To ensure that the chip functions properly, an

appropriate VOVP is required. The recommended

VOVP is about 1.1 to 1.2 times greater than VOUT

for normal operation. VOVP is set by an external

resistor on OVP, and can be calculated using

Equation (12):

HIGH

OVP

LOW

R

V

2(V) (1

)

R

=

 +

(12)

Where RHIGH and RLOW are the voltage divider

resistors between VOUT and GND.

Expanding LED Channels

The MP3383 can expand the number of LED

channels by using two or three ICs in parallel. To

connect two ICs for a total of eight LED strings,

connect the VCC pins of the master IC and the

slave IC together to power the slave IC

’s internal

logic circuitry. Connect the COMP pins of the

slave IC and the master IC together to regulate

the voltage of all eight LED strings. The slave

IC

’s MOSFET driving signal is not used. The

boost converter can be driven by the master IC

only. Do not leave t

he slave IC’s ISENSE pin

floating; connect it to ground. Apply the EN and

DIM signals to both ICs.