NXP Semiconductors OM13260, Installation Manual, Page: 28 / 71

NXP Semiconductors
UMxxxxx
Install Guide
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Preliminary 1
— September 6, 2013
© NXP B.V. 2013. All rights reserved.
28 of 70
Table 5.1 Bus Pull Up Resistors
Strength Position Value
(Ohms) Bus 1 SCL Bus 1
SDA
Bus 2
SCL Bus 2
SDA
L A 1100 R16 R13 R26 R23
M B 634 R15 R12 R25 R22
H C 324 R14 R11 R24 R21
5.3.3 LED Driver Slave (PCA9955)
Bus1 is also used to control the LED Driver (PCA9955, IC6). The LED Driver has constant current outputs
and is directly connected to the LEDs, without customary series resistors. The LEDs are powered
directly from the 5V supply, thus avoiding further power dissipation in the 3.3V linear regulator, IC1.
The sixteen channels drive eight LED clusters consisting of four White LEDs (LED12 – LED15) and four
RGB LED Clusters (LED0 – LED11). The maximum current available for each channel is set by R35 and
the variable resistor R36. The LEDs use the PCB top metal for heat dissipation, the LED driver is in the
HTSSOP28 package has a thermal pad ground connection, and operates from the main 3.3V supply. See
figure 5.12 and figure 5.13.
Fig 5.12 Bus1 LED Driver 16 channel