MP3306EG-LF-P Datasheet MP3306EG-LF-P, MP3306EG-LF-Z | P7-P9

MP3306-30V 700kHz SYNCHRONOUS STEP-UP WHITE LED DRIVER

MP3306 Rev.1.01 www.MonolithicPower.com 7

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OPERATION

The MP3306 uses a constant frequency, peak

current mode step up regulator architecture to

regulate the current flowing through series string of

white LEDs. The operation of the MP3306 can be

understood by referring to the block diagram of

Figure 1.

At the start of each oscillator cycle the low side FET

(M2) is turned on through the control circuitry. To

prevent sub-harmonic oscillations at duty cycles

greater than 50 percent, a stabilizing ramp is added

to the output of the current sense amplifier and the

result is fed into the positive input of the PWM

comparator. When this voltage equals the output

voltage of the error amplifier the power FET is

turned off. Then the inductor current flows into the

output capacitor and LED load through internal high

side N-channel MOSFET (M3), which forces the

inductor current to decrease.

The voltage at the output of the error amplifier is an

amplified version of the difference between the

200mV reference voltage and the feedback voltage.

In this way the LED current is regulated accurately.

If the feedback voltage starts to drop, the output of

the error amplifier increases. This result in more

current flowing through the high side power FET,

thus increasing the power charged in inductor and

delivered to the output.

MP3306 provides the analog and PWM dimming

solution, the internal resistor and external capacitor

one PWMO pin filters the PWM dimming signal on

PWMI pin to DC level that program the internal

reference to accomplish the analog dimming

function. When floating the PWMO pin, PWM

dimming function works.

Open Load protection shuts off the MP3306 if the

output voltage goes too high. In some cases an

LED may fail, this results in the feedback voltage

always being zero. The part then runs at maximum

duty cycle boosting the output voltage up. If the

output ever exceeds the programmable OVP

threshold, the MP3306 will shut down. The part

does not switch again until the EN pin or V

toggled.

During Shutdown mode when EN is low, the IC

keeps the internal high-side N-channel MOSFET

(M1) off to disconnect the output from input.

MP3306 has cycle by cycle current limit to protect

the load and IC from over current. And the internal

MOSFET (M1) limits the input current to prevent

system damage when short V

OUT

condition occurs.

MP3306-30V 700kHz SYNCHRONOUS STEP-UP WHITE LED DRIVER

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APPLICATION INFORMATION

VIN

DIM

GND

LED+

LED-

TP6

TP5

TP4

TP3

TP2

TP1

MP3306

912

BST

OUT

VCC

PWMI

PWMO OVP

GND

JP1

10nF

51k

205k

10k

Figure 2—3V~12V Input, Typical Application Driving 8 WLEDs in series

Figure 2 shows a typical application circuit that

can drive up to 8 white LEDs with 20mA. A

0.22~2.2µF output capacitor is sufficient for most

applications. The inductor with low DC inductor

resistance (DCR) will improve efficiency. Two

4.7μF ceramic capacitors provide sufficient input

decoupling.

Selecting the Inductor

The inductor forces a higher output voltage

driven from a lower input voltage. A larger

inductor value results in less ripple current, a

lower peak inductor current, and reduces stress

on the internal N-Channel MOSFET. However,

larger-value inductor has a larger physical

footprint, higher series resistance, and lower

saturation current.

Choose an inductor that does not saturate under

the worst-case load conditions. Calculate the

required inductance value using the following

equations:

OUT

SW LOAD

η V D(1D)

2 f I

×××−

≥

××

OUT

=−

Where V

and V

OUT

are the input and output

voltages, f

is the switching frequency, I

LOAD

the LED load current, and η is the efficiency.

Setting the LED Current

The LED current is controlled by the current

setting resistor, R1. The current through the

LEDs is given by: I

LED

= 202mV/R1.

Table 1 shows the selection of resistors for a

given LED current.

Table 1—I

LED

vs. R1 RSET

LED

(mA) R1 (Ω)

1 200

5 40

10 20

20 10

60 3.33

180 1.11

200 1

The internal ramped compensation voltage

added to the current sense amplifier reduces the

maximum output current as the duty cycle

increases. As more LEDs are added, the output

voltage rises but the maximum current delivered

to the load falls as well. Figure 3 shows the

current limit curve, and the max LED current is

gotten as the formula.

LOAD(max) PK

I(I )(1D)0.8

2Lf

=− ×−×

××

Where, I

is the peak current corresponding duty

cycle from current limit curve, the L is inductor,

the 0.8 means the margin coefficient.

MP3306-30V 700kHz SYNCHRONOUS STEP-UP WHITE LED DRIVER

MP3306 Rev.1.01 www.MonolithicPower.com 9

6/15/2015 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.

Current Limit vs. Duty Cycle

0 10 20 30 40 50 60 70 80 90 100

0.5

1.5

Figure 3—Current Limit Curve

Analog and PWM Dimming

MP3306 provides 2 types of dimming solutions,

analog dimming and PWM dimming.

For analog, connect an external capacitor on

PWMO pin to form the low pass filter with internal

resistor R, the PWM dimming signal on PWMI pin

is filtered to DC signal to set the internal

reference to accomplish the analog dimming. The

time constant should be ten times greater than a

PWM waveform cycle:

PWMRC 10 T>⋅

For PWM dimming, floating PWMO pin and apply

the PWM dimming signal on PWMI pin.

Setting Over Voltage Protection Threshold

Open Load protection will shut off the MP3306 if

the output voltage goes too high. In some cases

an LED may fail, this will result in the feedback

voltage always being zero. The part boots the

output voltage higher and higher. If the output

voltage ever exceeds the programmed OVP

threshold as the formula,

OVP

V =1.22 (1 R2 /R3)×+

The MP3306 will shut down. The part will not

switch again until the power is recycled.

Layout Considerations

Careful attention must be paid to the PCB board

layout and components placement. Proper layout

of the high frequency switching path is critical to

prevent noise and electromagnetic interference

problems. The loop of MP3306’s internal low side

MOSFET, synchronous MOSFET, and output

capacitor is flowing with high frequency ripple

current, it must be minimized. So the output

capacitor should be placed to IC as close as

possible.

P1-P3 P4-P6 P7-P9 P10-P12

MP3306EG-LF-P

Mfr. #:

Buy MP3306EG-LF-P

Manufacturer:

Monolithic Power Systems (MPS)

Description:

LED Lighting Drivers 30V WLED Driver with Int Disconnect FET

Lifecycle:

New from this manufacturer.

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MP3306EG-LF-P

MP3306EG-LF-P

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