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PC Board Layout

Step 2: Determine the capacitors

: A high quality ceramic capacitor for decoupling should be connected from the VIN pin to ground. In

this LM3466 evaluation board, a 100 V, 0.01 µF ceramic capacitor is used.

: If the cable connecting the LED string and the evaluation board is long, the parasitic inductance of the

cable may generate noise. If this happens, a high quality ceramic capacitor should be connected between

the ILED pin and ground. In this LM3466 evaluation board, a 100V, 1 µF ceramic capacitor is used.

Step 3: Determine other components

and C

: The VEQ pins of all LM3466 are shorted together and then connected to ground through

and C

for normal operation. Only one R

and one C

are required for one lighting system. It is

recommended that R

be 51.1Ω and C

be 1 µF.

Step 4: Optional circuit for fault reporting

For simplicity, the COMM pins of all LM3466 can be shorted directly to a common bus COMM_ALL for

normal operation (R

= 0 Ω). If fault reporting upon LED string open of a corresponding channel is

required, an optional circuit can be used to connect the COMM pin of each LM3466 to COMM_ALL. Since

the COMM pin pulls low during LED string open, the small signal LED in the optional circuit shown in

Figure 6 will light during a fault.

Figure 6. Optional COMM Circuit

4 PC Board Layout

To minimize the effect of noise, the ground connections of the LM3466 and the sense resistor R

should

be closed. Good heat dissipation helps optimize the performance of the LM3466. The ground plane should

be used to connect the exposed pad of the LM3466, which is internally connected to the LM3466 die

substrate. The area of the ground plane should be extended as much as possible on the same copper

layer above and below the LM3466. Using numerous vias beneath the exposed pad to dissipate heat of

the LM3466 to another copper layer is also a good practice.

SNOA566A–October 2011–Revised April 2013 AN-2182 LM3466 Demonstration Board Reference Design

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