MP3394SGF Datasheet MP3394SGF, MP3394SGY-Z, MP3394SGS | P10-P12

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For external PWM dimming, ground the BOSC

pin through a resistor, and apply an external

PWM signal to the DBRT pin.

For DC-input PWM dimming, apply a DC analog

signal to the DBRT pin, and connect a capacitor

on BOSC pin to ground. The DC signal is then

converted to a DPWM dimming signal with a

proportional oscillation frequency.

The brightness of the LED array is proportional to

the duty cycle of the DPWM signal. The DPWM

signal frequency is set by the capacitor from the

BOSC pin to ground.

Open String Protection

Open string protection is achieved through the

OVP pin and the LED (1 to 4) pins. If one or more

strings are open, the respective LEDX pins are

pulled to ground and the IC keeps charging the

output voltage until it reaches the over-voltage

protection (OVP) threshold. Then the chip marks

off the strings which have an LEDX pin voltage

lower than 196mV. Once marked, the remaining

LED strings force the output voltage back into

tight regulation. The string with the largest

voltage drop determines the output regulation.

The MP3394S will always attempt to light at least

one string. If all strings are open, the MP3394S

shuts down the step-up converter. The strings

will remain in this marked state until the chip

reset.

Short String Protection

The MP3394S monitors the LEDX pin voltages to

determine if a short string fault has occurred. If

one or more strings are shorted, the respective

LEDX pins tolerate high voltage stress. If an

LEDX pin voltage is higher than 6.1V, this

condition triggers the detection of a short string.

When a short string faults (LEDX over-voltage

fault) keeps for 4096 switching clocks, the fault

string is marked OFF and disabled. Once a string

is marked OFF, it disconnects from the output

voltage loop. The marked LED strings shut off

completely until the part restarts. If all strings are

shorted, the MP3394S will shut down the step-up

converter. The strings remain marked OFF until

the chip resets.

Thermal Shut Down Protection

When MP3394S die temperature exceeds the

thermal protection threshold, the thermal

protection is triggered. IC shuts down until EN

restart.

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APPLICATION INFORMATION

Selecting the Switching Frequency

The switching frequency of the step-up converter

is recommended from 100kHz to 500kHz for

most of application. An oscillator resistor on OSC

pin sets the internal oscillator frequency for the

step-up converter according to the equation:

OSC

69190

f(kHz)

R(k)

For R

OSC

=374k, the switching frequency is set

to 185 kHz.

Setting the LED Current

The LED string currents are identical and set

through the current setting resistor on the ISET

pin. The ISET pin can not be open.

LED

SET

800 1.22V

I(mA)

(R 0.5)k

+Ω

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, use a 4.7F ceramic capacitor

in parallel with a 220µF electrolytic capacitor.

Selecting the Inductor and Current Sensing

Resistor

The MP3394S 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, resulting in lower peak

inductor current and reducing stress on the

internal N-channel MOSFET. However, the 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

with high efficiency and good EMI performance.

Calculate the required inductance value using the

equation:

OUT

SW LOAD

 V D

(

)

2 f I

×××−

≥

××

OUT

1D −=

Where V

and V

OUT

are the input and output

voltages, f

is the switching frequency, I

LOAD

the LED load current, and  is the efficiency.

The switching current is usually used for the peak

current mode control. In order to avoid hitting the

current limit, the voltage across the sensing

resistor R

SENSE

must measure less than 80% of

the worst-case current-limit voltage, V

SENSE

L(PEAK)

0.8 V

OUT LOAD IN OUT IN

L(PEAK)

IN SW OUT

VI V(V-V)

V 2LfV

××

×× ×

Where I

L(PEAK)

is the peak value of the inductor

current. V

SENSE

is shown in Figure 3.

CURRENT LIMIT-VSENSE (mV)

DUTY CYCLE (%)

Vsense vs. Duty Cycle

100

200

300

400

500

0 102030405060708090100

Figure 3—V

SENSE

vs Duty Cycle

Selecting the Power MOSFET

The MP3394S is capable of driving a wide variety

of N-channel power MOSFETS. The critical

parameters of selection of a MOSFET are:

1. Maximum drain-to-source voltage, V

DS(MAX)

2. Maximum current, I

D(MAX)

On-resistance, R

DS(ON)

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4. Gate source charge Q

and gate drain

charge Q

5. Total gate charge, Q

Ideally, the off-state voltage across the MOSFET

is equal to the output voltage. Considering the

voltage spike when it turns off, V

DS(MAX)

should be

greater than 1.5 times of the output voltage.

The maximum current through the power

MOSFET occurs at the maximum input voltage

and the maximum output power. The maximum

RMS current through the MOSFET is given by

RMS(MAX) IN(MAX) MAX

IID=×

, where:

OUT IN(MIN)

MAX

OUT

−

≈

The current rating of the MOSFET should be

greater than 1.5xI

RMS

The ON resistance of the MOSFET determines

the conduction loss, which is given by:

kRIP

(on) DS

RMScond

××=

Where k is the temperature coefficient of the

MOSFET.

The switching loss is related to Q

and Q

GS1

which determine the commutation time. Q

GS1

the charge between the threshold voltage and

the plateau voltage when a driver charges the

gate, which can be read in the chart of V

vs. Q

of the MOSFET datasheet. Q

is the charge

during the plateau voltage. These two

parameters are needed to estimate the turn-on

and turn-off losses.

GS1 G

SW DS IN SW

DR TH

GD G

DS IN SW

DR PLT

PVIf

VIf

=×××+

−

×××

−

Where V

is the threshold voltage, V

PLT

is the

plateau voltage, R

is the gate resistance, and

is the drain-source voltage. Please note that

calculating the switching loss is the most difficult

part in the loss estimation. The formula above

provides a simplified equation. For more accurate

estimates, the equation becomes much more

complex.

The total gate charge, Q

, is used to calculate

the gate drive loss. The expression is

SWDRGDR

fVQP ××

Where V

is the drive voltage.

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

4.7F ceramic capacitor in parallel with a 22F

electrolytic capacitor will suffice.

Setting the Over Voltage Protection

The open string protection is achieved through

the detection of the voltage on the OVP pin. In

some cases, an LED string failure results in the

feedback voltage always zero. The part then

keeps boosting the output voltage higher and

higher. If the output voltage reaches the

programmed OVP threshold, the protection will

be triggered.

To ensure the chip functions properly, select the

resistor values for the OVP resistor divider to

provide an appropriate set voltage. The

recommended OVP point is about 1.1 to 1.2

times higher than the output voltage for normal

operation.

HIGH

OVP

LOW

V1.23(1 )

=×+

Selecting Dimming Control Mode

The MP3394S provides two different dimming

methods

1. Direct PWM Dimming

An external PWM dimming signal is employed to

achieve PWM dimming control. Connect a 100k

resistor from BOSC pin to GND and apply a

PWM dimming signal—in the range of 100Hz to

20kHz—to the DBRT pin. The minimum

recommended amplitude of the PWM signal is

1.2V. The low level should be less than 0.4V

(See Figure 4).

P1-P3 P4-P6 P7-P9 P10-P12 P13-P15 P16-P17

MP3394SGF

Mfr. #:

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Manufacturer:

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Description:

LED Lighting Drivers 4-String Max 200m A/White LED Drvr

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MP3394SGF

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