The PCA9955B is an 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 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 PCA9955B 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 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 PCA9955B 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 PCA9955B 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, PCA9955B has a unique Sub Call address to identify it as a 16-channel LED driver. This unique address allows mixing of devices with different channel widths. Three hardware address pins on PCA9955B allow up to 125 devices on the same bus.
The Software Reset (SWRST) function allows the master to perform a reset of the PCA9955B 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 condition.
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## Features
* 16 LED drivers. Each output programmable at:
* Off
* On
* Programmable LED brightness
* Programmable group dimming/blinking mixed with individual LED brightness
* Programmable LED output delay to reduce EMI and surge currents
* Gradation control for all channels
* Each channel can assign to one of four gradation control groups
* Programmable gradation time and rate for ramp-up and/or ramp-down operations
* Programmable step time (6-bit) from 0.5 ms (minimum) to 512 ms (maximum)
* Programmable hold-on time after ramp-up and hold-off time after ramp-down (3-bit) from 0 s to 6 s
* Programmable final ramp-up and hold-on current
* Programmable brightness current output adjustment, either linear or exponential curve
* 16 constant current output channels can sink up to 57 mA, tolerate up to 20 V when OFF
* Output current adjusted through an external resistor (REXT input)
* Output current accuracy:
* ±4 % between output channels
* ±6 % between PCA9955B devices
* Open/short load/overtemperature detection mode to detect individual LED errors
* 1 MHz Fast-mode Plus compatible I2C-bus interface with 30 mA high drive capability on SDA output for driving high capacitive buses
* 256-step (8-bit) linear programmable brightness per LED output varying from fully off (default) to maximum brightness fully ON using a 31.25 kHz PWM signal
* 256-step group brightness control allows general dimming (using a 122 Hz PWM signal) from fully off to maximum brightness (default)
* 256-step group blinking with frequency programmable from 15 Hz to 16.8 s and duty cycle from 0 % to 99.6 %
* Output state change programmable on the Acknowledge or the STOP condition to update outputs byte-by-byte or all at the same time (default to ‘Change on STOP’).
* Active LOW Output Enable (OE) input pin allows for hardware blinking and dimming of the LEDs
* Three quinary hardware address pins allow 125 PCA9955B devices to be connected to the same I2C-bus and to be individually programmed
* 4 software programmable I2C-bus addresses (one LED Group Call address and three LED Sub Call addresses) allow groups of devices to be addressed at the same time in any combination (for example, one register used for ‘All Call’ so that all the PCA9955Bs on the I2C-bus can be addressed at the same time and the second register used for three different addresses so that 1⁄3 of all devices on the bus can be addressed at the same time in a group). Software enable and disable for each programmable I2C-bus address.
* Unique power-up default Sub Call address allows mixing of devices with different channel widths
* Software Reset feature (SWRST Call) allows the device to be reset through the I2C-bus
* 8 MHz internal oscillator requires no external components
* Internal power-on reset
* Noise filter on SDA/SCL inputs
* No glitch on LEDn outputs on power-up
* Low standby current
* Operating power supply voltage (VDD) range of 3 V to 5.5 V
* 5.5 V tolerant inputs on non-LED pins
* -40 °C to +105 °C operation
* ESD protection exceeds 4000 V HBM per JESD22-A114
* Latch-up testing is done to JEDEC Standard JESD78 which exceeds 100 mA
