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The PCU9955A is an Ultra Fast-mode (UFm) I²C-bus controlled 16-channel constant
current LED driver optimized for dimming and blinking 57 mA Red/Green/Blue/Amber
(RGBA) LEDs in amusement products. Each LED output has its own 8-bit resolution (256
steps) fixed frequency individual PWM controller that operates at 31.25 kHz with a duty
cycle that is adjustable from 0 % to 100 % to allow the LED to be set to a specific
brightness value. An additional 8-bit resolution (256 steps) group PWM controller has both
a fixed frequency of 122 Hz and an adjustable frequency between 15 Hz to once every
16.8 seconds with a duty cycle that is adjustable from 0 % to 99.6 % that is used to either
dim or blink all LEDs with the same value.
Each LED output can be off, on (no PWM control), set at its individual PWM controller
value or at both individual and group PWM controller values. The PCU9955A operates
with a supply voltage range of 3 V to 5.5 V and the constant current sink LED outputs
allow up to 20 V for the LED supply. The output peak current is adjustable with an 8-bit
linear DAC from 225 μA to 57 mA.
Gradation control for all current sources is achieved via the I²C-bus serial interface and
allows user to ramp current automatically without MCU intervention. 8-bit DACs are
available to adjust brightness levels for each LED current source. There are four
selectable gradation control groups and each group has independently four registers to
control ramp-up and ramp-down rate, step time, hold ON/OFF time and final hold ON
output current. Two gradation operation modes are available for each group, one is single
shot mode (output pattern once) and the other is continuous mode (output pattern repeat).
Each channel can be set to either gradation mode or normal mode and assigned to any
one of these four gradation control groups.
This device has built-in overtemperature detection circuitry. A thermal shutdown feature
protects the device when internal junction temperature exceeds the limit allowed for the
The PCU9955A device is the first LED controller device in a new Ultra Fast-mode (UFm)
I²C-bus family. UFm I²C-bus devices offer higher frequency (up to 5 MHz). The UFm
I²C-bus slave devices operate in receive-only mode. That is, only I²C writes to the
PCU9955A are supported. As such, there are no status registers in PCU9955A. The
PCU9955A allows significantly higher data transfer rate compared to the Fast-mode Plus
The active LOW output enable input pin (OE) blinks all the LED outputs and can be used
to externally PWM the outputs, which is useful when multiple devices must be dimmed or
blinked together without using software control.
Software programmable LED Group and three Sub Call I²C-bus addresses allow all or
defined groups of PCU9955A devices to respond to a common I²C-bus address, allowing
for example, all red LEDs to be turned on or off at the same time or marquee chasing
effect, thus minimizing I²C-bus commands. On power-up, PCU9955A has a unique
Sub Call address to identify it as a 16-channel LED driver. This allows mixing of devices
with different channel widths. Three hardware address pins on PCU9955A allow up to
125 devices on the same bus.
The Software Reset (SWRST) function allows the master to perform a reset of the
PCU9955A through the I²C-bus, identical to the Power-On Reset (POR) that initializes the
registers to their default state causing the output current switches to be OFF (LED off).
This allows an easy and quick way to reconfigure all device registers to the same