LM3464MH datasheet(16/22 Pages) NSC

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LM3464/64A. This function is applicable to both single

LM3464/64A and cascade operation modes.

EXPANDING NUMBER OF OUTPUT CHANNEL

The LM3464/64A can be cascaded to expand the number of

output channel. Bases on the master-slave architecture, one

of the LM3464/64A in the system must be set to master mode

and the rest must be set to slave mode. Figure 15 shows an

example application circuit that provides eight output chan-

nels.

To enable cascade operation, the SYNC pin of the master

LM3464/64A should connect to the DIM pin of the first slave

device and similarly the SYNC pin of such slave device should

connect to its down stream slave device for startup synchro-

nization. In addition, the OutP pins of all the LM3464/64A

have to tie up though a diode and resistor R

DHC to the voltage

feedback node of the primary power supply to accomplish

dynamic headroom control, as shown in Figure 15.

The slave devices can only be commanded by the master

LM3464/64A. With the master and slave devices linked up,

the information of startup synchronization, thermal foldback

and PWM dimming controls are gathered by the master de-

vice and distribute stage by stage through the SYNC pin.

To set a LM3464/64A in master mode, the voltage of the

VLedFB pin must be set below 3.25V. When the VLedFB pin

is connected to VCC, the device is in slave mode. In slave

mode, local thermal foldback and PWM controls are overrid-

den by the packaged synchronization signal delivered from

the master.

CONNECTION TO LED ARRAYS

When LEDs are connected to the LM3464/64A driver stage

through long cables, the parasitic components of the cable

harness and external MOSFETs may resonant and eventu-

ally lead to unstable system operation. In applications that the

cables between the LM3464/64A driver circuit and LED light

engine are longer than 1 meter, a 4.7k

Ω resistor should be

added across the GDx pins to GND as shown in Figure 12.

30115043

FIGURE 12. Additional Resistor Across GDx and SEx for

Cable Harness Over 1m Long

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