16-channel SPI serial bus 57 mA/20 V constant current LED driver

The PCA9745B is a daisy-chain SPI-compatible 4-wire serial bus controlled 16-channel constantcurrent 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 cyclethat is adjustable from 0 % to 100 % to allow the LED to be set to a specific brightnessvalue. An additional 8-bit resolution (256 steps) group PWM controller has both a fixedfrequency of 122 Hz and an adjustable frequency between 15 Hz to once every 16.8 secondswith a duty cycle that is adjustable from 0 % to 99.6 % that is used to either dim orblink all LEDs with the same value.

Each LED output can be off, on (no PWM control), set at its individual PWM controllervalue or at both individual and group PWM controller values. The PCA9745B operates witha supply voltage range of 3 V to 5.5 V and the constant current sink LED outputs allowup to 20 V for the LED supply. The output peak current is adjustable with an 8-bitlinear DAC from 225 μA to 57 mA.

Gradation control for all current sources is achieved via the 4-wire serial bus interfaceand allows user to ramp current automatically without MCU intervention. 8-bit DACs areavailable to adjust brightness levels for each LED current source. There are fourselectable gradation control groups and each group has independently four registers tocontrol ramp-up and ramp-down rate, step time, hold ON/OFF time and final hold ON outputcurrent. Two gradation operation modes are available for each group, one is single shotmode (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 oneof these four gradation control groups.

This device has built-in open, short load and overtemperature detection circuitry. Theerror information from the corresponding register can be read via the 4-wire serial bus.Additionally, a thermal shutdown feature protects the device when internal junctiontemperature exceeds the limit allowed for the process.

The PCA9745B device is designed to use 4-wire read/write serial bus with higher dataclock frequency (up to 25 MHz).

The active LOW output enable input pin (OE) blinks all theLED outputs and can be used to externally PWM the outputs, which is useful when multipledevices need to be dimmed or blinked together without using software control.