The PCA9745B is a daisy-chain SPI-compatible 4-wire serial 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 PCA9745B 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 4-wire serial bus 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 4-wire serial bus. Additionally, a thermal shutdown feature protects the device when internal junction temperature exceeds the limit allowed for the process.
The PCA9745B device is designed to use 4-wire read/write serial bus with higher data clock frequency (up to 25 MHz).
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.