The PCA9956B 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 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 PCA9956B operates with
a supply voltage range of 3 V to 5.5 V and the constant current sink LED outputs to 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 a 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 an
internal junction temperature exceeds the limit allowed for the process.
The PCA9956B 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
The active LOW output enables 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 PCA9956B 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, PCA9956B 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 PCA9956B
allow up to 125 devices on the same bus.
The Software Reset (SWRST) function allows the master to perform a reset of the PCA9956B
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