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The PCA9956A is an I²C-bus controlled 24-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 99.6 % 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
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 PCA9956A 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.
This device has built-in open, short load and overtemperature detection circuitry. The error
information from the corresponding register can be read via the I²C-bus. Additionally, a
thermal shutdown feature protects the device when internal junction temperature exceeds
the limit allowed for the process.
The PCA9956A device has a Fast-mode Plus (Fm+) I²C-bus interface. Fm+ devices offer
higher frequency (up to 1 MHz) or more densely populated bus operation (up to 4000 pF).
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 need to 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 PCA9956A 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, PCA9956A will have a unique
Sub Call address to identify it as a 24-channel LED driver. This allows mixing of devices
with different channel widths. Three hardware address pins on PCA9956A allow up to
125 devices on the same bus.
The Software Reset (SWRST) function allows the leader to perform a reset of the
PCA9956A 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