MP3394—4-STRING, MAX 200mA/STRING WHITE LED DRIVER

MP3394 Rev. 1.07

www.MonolithicPower.com

13

3/21/2013

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BOSC

DBRT

MP3394

PWM Dimming

100Hz~20kHz

R1

100 kO

Figure 4—Direct PWM Dimming

Table 1 shows the PWM dimming duty Range

with different PWM dimming frequency.

Table 1—The Range of PWM Dimming Duty

Fpwm(Hz)

Dmin

Dmax

100<f

≤200

0.30%

100%

200<f

≤500

0.75%

100%

500<f

≤1k

1.50%

100%

1k<f

≤2k

3.00%

100%

2k<f

≤5k

7.50%

100%

5k<f

≤10k

15.00%

100%

10k<f

≤20k

30.00%

100%

2. DC Input PWM Dimming

To apply DC input PWM dimming, apply an

analog signal (range from 0.2 V to 1.2V) to the

DBRT pin to modulate the LED current directly. If

the PWM dimming signal is applied with a lower

0.2V DC voltage, the PWM duty cycle will be 0%.

If the DBRT pin is applied with a DC

voltage>1.2V, the output will be 100% (See

Figure 5). The capacitor on BOSC pin set the

frequency of internal triangle waveform according

to the equation.

The dimming frequency is recommended set

from 100Hz to 20kHz.

C1

BOSC

DBRT

MP3394

DC Signal

Figure 5—DC input PWM Dimming

Extending LED Channels applications

The MP3394 is flexible for extending LED

channels with two or three MP3394s in parallel.

For the connection of two MP3394s extending 8

strings LEDs, tie the VCC pins of the master IC

and the slave IC together to provide the power of

the slave IC internal logic circuitry. Also tie the

COMP pins of the slave IC and the master IC

together to regulate the voltage of all 8 strings

LEDs. The MOS driving signals of the slave IC

are not used; the boost converter can be only

driven by the master IC. Do not let the Isense pin

of the slave IC floating, tie it to GND. The EN and

Dimming signals should be applied to both ICs. It

is recommended to use external PWM dimming

mode

to

achieve

the

accurate

dimming

synchronization of both parts.

External MOSFET for Short Protection

When output voltage is higher than rating of

LED1-4 pins, external MOSFET is needed for

each LED channel to avoid destroying LED1-4

pins. (See Figure 8)The rating of MOSFET must

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 external MOSFET (M1),

output diode (D1), and output capacitor (C2, C3)

flowes with high frequency pulse current. It must

be as small as possible (See Figure 6).

Figure 6—Layout Consideration

All logic signals and power ground are referred to

the GND. The power ground should be externally

connected to signal ground and is recommended

to keep away from the logic signals.