描述 Description

The PCA9957 is a daisy-chain SPI-compatible 4-wire serial bus controlled 24-channel constant current LED driver optimized for dimming and blinking 32 mA Red/Green/Blue/Amber (RGBA) LEDs.
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 PCA9957 operates with a supply voltage range of 2.7 V to 5.5 V and the constant current sink LED outputs allow up to 5 V for the LED supply. The output peak current is adjustable with an 8-bit linear DAC from 125 μA to 31.875 mA with REXT = 2 kΩ.

特性 Features

? 24 LED drivers. Each output programmable at:
? Off
? On
? 8 bits programmable LED brightness
? 8 bits 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 be assigned to one of six 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
? 24 constant current output channels can sink up to 32 mA, and tolerate up to 5.5 V when OFF
? Output current adjusted through an external resistor (REXT input)
? Output current accuracy
? ±6.5 % absolute accuracy with 30 mA output current
? Maximum ±4 % channel to channel variation
? Maximum ±6 % device to device variation
? Open/short load/overtemperature detection mode to detect individual LED errors
? 4-wire serial bus interface with 10 MHz data clock rate
? 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 %
? Active LOW Output Enable (OE) input pin allows for hardware blinking and dimming of the LEDs
? 8 MHz internal oscillator requires no external components
? Internal power-on reset
? No glitch on LEDn outputs on power-up
? Low standby current
? Operating power supply voltage (VDD) range of 2.7 V to 5.5V
? 5.5 V tolerant inputs on non-LED pins
? -40 °C to +85 °C operation
? Latch-up performance exceeds 100 mA per JESD 78, Class II
? ESD protection exceeds
? 2 kV Human-Body Model (A114-A)
? 1 kV Charged-Device Model (C101)
? Package offered: HVQFN40

應(yīng)用 Application

Industrial

? Fade-in and fade-out for breathlight control

? LCD backlights

? LED displays

? LED status information

? RGB or RGBA LED drivers