PCB layout guidelines

AN4374

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DocID025366 Rev 2

example, with 1 MHz CLK frequency, an adequate value could be 15 ns (e.g. 100

Ohm + 150 pF).

Figure 21. Interface signal filtering

Radiated emission reduction (EMI)

–

In order to decrease the electromagnetic noise during LED power-on/off, the driver

output lines should follow the shortest path "power rail/LED/driver". Besides, in

order to keep the system stability, a good electrolytic capacitor should be

connected to the power supply rail as near as possible the LED anodes (the

inductive LED power supply rail component should be compensated by added

capacitance; in case of wide PCB, place more distributed capacitors). Another

–

Shorten as minimum as possible the SPI connection strips (from controller to LED

driver).

Device thermal management

–

In order to improve the power dissipation (to decrease the device working

temperature), solder the package exposed pad (if available) to the board.

–

In order to improve the thermal performance at least a 4-layer (e.g. 2S2P) PCB

should be used.

–

The copper area below the package thermal pad should be as large as possible,

outside the package perimeter (using the package sides without pins).

–

A reasonable number of vias must connect the copper area below the package to

all available PCB layers especially just below the device package (e.g. 3x3 or 4x3

vias array) but also outside the package perimeter. Smaller and closely spaced

poor signal

good signal

CLK, LE, etc.

CLK, LE, etc.

Proper filtering to

improve digital

signal quality

AM16870v1