The total output power of the LED lighting system can be ex-
panded by cascading the LM3464A evaluation boards. In
cascade operation, the system involves one master unit and
multiple slave units. Both master and slave units are
LM3464A evaluation boards with minor modifications to pro-
gram the LM3464A into master or slave modes. The connec-
tion diagram for cascade operation is shown in figure 8. The
master unit is responsible to provide functions as listed in be-
low:
1. Detect rail voltage upon system startup
2. Command slave units to turn on LEDs as its VLedFB volt-
age reaches 2.5V
3. Provide dimming signal to slave units according to the
PWM dimming signal received at its DIM pin
4. Provide dimming signal to slave units according to the volt-
age of its Thermal pin
By default, the LM3464A evaluation board is set to master
mode. To set the board to slave mode, the following changes
to the board are required:
• Remove resistors RFB1 and RFB2
• Connect VLEDFB to VCC
When connecting the master and slaves, the following con-
nections are required:
• Connect the VIN terminal of master and slave units together
and then to the POSITIVE output of the AC/DC power supply
• Connect the PGND terminal of master and slave units to-
gether and then to the NEGATIVE output of the AC/DC power
supply
• Connect the SYNC terminal of the master unit to DIM ter-
minal of the next slave unit in the chain.
• Connect the VFB terminal of master and slave units together
and then to the voltage feedback node of the AC/DC power
supply.
If more than one slave unit is required, the SYNC pin of the
first slave unit should connect to the DIM pin of the next slave
unit to allow propagation of the control signal along the system
chain.
Connection To Led Arrays
When LEDs are connected to the LM3464A 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 LM3464A driver circuit and LED light en-
gine are longer than 1 meter, a 4.7k
Ω
resistor should be
added across the GDx pins to GND as shown in Figure 12.
30127164
FIGURE 9. Additional Resistor Across GDx and SEx for
Cable Harness Over 1m Long
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