MP3399-12-STRING, CASCADING WHITE LED DRIVER WITH STEP-UP CONTROLLER

MP3399 Rev. 1.0

www.MonolithicPower.com

14

3/27/2013

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Figure 4—DC input PWM Dimming

Extending LED Channels applications

The MP3399 is flexible for extending LED

channels with two or more MP3399s in parallel.

For the connection of two MP3399s extending 24

strings LEDs, please see the typical application

diagram in page 2. 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

24 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.

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 (M2),

output diode (D1), and output capacitor (C5) is

flowing with high frequency pulse current. It must

be as small as possible (See Figure 5).

Figure 5—Layout Consideration

The IC exposed pad is internally connected to

GND pin, and all logic signals are refer to the

GND. The PGND should be externally connected

to GND and is recommended to keep away from

the logic signals.

External MOSFET for Short Protection

When output voltage is higher than rating of

LED1-12 pins, external MOSFET is needed for

each LED channel to avoid destroying LED1 -12

pins. (See Figure 8 for 4 channels application)

The rating of MOSFET must be higher than 1.2*