NXP Semiconductors
UM11761
PCA9955BTW-ARD evaluation board
J88 position
J87 position
J86 position
I
2
C target address (HEX)
1-2
OFF
OFF
B0h
2-3
1-2
1-2
58h
2-3
1-2
2-3
54h
2-3
1-2
OFF
56h
2-3
2-3
1-2
44h
2-3
2-3
2-3
40h
2-3
2-3
OFF
42h
2-3
OFF
1-2
4Eh
2-3
OFF
2-3
4Ah
2-3
OFF
OFF
4Ch
OFF
1-2
1-2
8Ah
OFF
1-2
2-3
86h
OFF
1-2
OFF
88h
OFF
2-3
1-2
76h
OFF
2-3
2-3
72h
OFF
2-3
OFF
74h
OFF
OFF
1-2
80h
OFF
OFF
2-3
7Ch
OFF
OFF
OFF
7Eh
Table 1. I
2
C target address chart
...continued
Alongside the I
2
C-bus, the circuit contains three control lines: the OE, RESET, and
MUX (REXT). In the block diagram the control lines are drawn with purple. The OE and
RESET lines control the corresponding OE and RESET inputs of the PCA9955B IC (U2,
pin 5, and 25). Driving low the OE input, enables all sixteen outputs of the LED driver.
Driving low the RESET input, sets the internal registers of PCA9959B to their default
state. For more details, see PCA9955B datasheet (NXP Semiconductors).
The limit current for each output of PCA9955B is set by a resistor connected between
REXT (U2, pin 1) and ground. The switch U5 allows to select two values for current limit:
20 mA (U1 – OFF), and 50 mA (U1 – ON). The state of U1 switch is controlled through
the MUX (REXT) line.
All control lines (purple color in the block diagram picture) are connected to the
expansion connectors J45 and J89. For more details, see the schematic diagram of the
PCA9955BTW-ARD board.
The PCA995B features sixteen LED drivers (PWM controlled, current sink sources).
Three RGB LEDs are allocated to the first outputs (LED0 to LED8). The outputs LED9
to LED15 drives white LEDs. The LEDs can be disconnected from the IC outputs with
jumpers.
The RGB LED D16 has jumpers connected in parallel for short testing. The jumpers J76
to J81 allows the user to redirect the corresponding output lines of D16 and D17 RGB
LEDs from the on-board LEDs to the RGB LED external connectors (J21 and J26). Using
the connectors, the user can easily attach external LEDs for testing. In the same manner,
UM11761
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User manual
Rev. 1.0 — 18 March 2022
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