The PCA9685 is an I²C-bus controlled 16-channel LED controller optimized for
Red/Green/Blue/Amber (RGBA) color backlighting applications. Each LED output has its
own 12-bit resolution (4096 steps) fixed frequency individual PWM controller that operates
at a programmable frequency from a typical of 24 Hz to 1526 Hz with a duty cycle that is
adjustable from 0 % to 100 % to allow the LED to be set to a specific brightness value.
All outputs are set to the same PWM frequency.
Each LED output can be off or on (no PWM control) or set at its individual PWM controller
value. The LED output driver is programmed to be either open-drain with a 25 mA current
sink capability at 5 V or totem pole with a 25 mA sink, 10 mA source capability at 5 V. The
PCA9685 operates with a supply voltage range of 2.3 V to 5.5 V and the inputs and
outputs are 5.5 V tolerant. LEDs can be directly connected to the LED output (up to
25 mA, 5.5 V) or controlled with external drivers and a minimum amount of discrete
components for larger current or higher voltage LEDs.
The PCA9685 is in the new Fast-mode Plus (Fm+) family. Fm+ devices offer higher
frequency (up to 1 MHz) and more densely populated bus operation (up to 4000 pF).
Although the PCA9635 and PCA9685 have many similar features, the PCA9685 has
some unique features that make it more suitable for applications such as LCD or LED
backlighting and Ambilight:
- The PCA9685 allows staggered LED output on and off times to minimize current
surges. The on and off time delay is independently programmable for each of the
16 channels. This feature is not available in PCA9635
- The PCA9685 has 4096 steps (12-bit PWM) of individual LED brightness control. The
PCA9635 has only 256 steps (8-bit PWM)
- When multiple LED controllers are incorporated in a system, the PWM pulse widths
between multiple devices may differ if PCA9635s are used. The PCA9685 has a
programmable prescaler to adjust the PWM pulse widths of multiple devices
- The PCA9685 has an external clock input pin that will accept user-supplied clock
(50 MHz max.) in place of the internal 25 MHz oscillators. This feature allows
synchronization of multiple devices. The PCA9635 does not have an external clock input
- Like the PCA9635, PCA9685 also has a built-in oscillator for the PWM control.
However, the frequency used for PWM control in the PCA9685 is adjustable from
about 24 Hz to 1526 Hz as compared to the typical 97.6 kHz frequency of the
PCA9635. This allows the use of PCA9685 with external power supply controllers. All
bits are set at the same frequency
- The Power-On Reset (POR) default state of LEDn output pins is LOW in the case of
PCA9685. It is HIGH for PCA9635
The active LOW Output Enable input pin (OE) allows asynchronous control of the LED
outputs and can be used to set all the outputs to a defined I²C-bus programmable logic
state. The OE can also be used to externally ‘pulse width modulate’ the outputs, which is
useful when multiple devices need to be dimmed or blinked together using software
Software programmable LED All Call and three Sub Call I²C-bus addresses allow all or
defined groups of PCA9685 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. Six hardware address pins allow up to
62 devices on the same bus.
The Software Reset (SWRST) General Call allows the master to perform a reset of the
PCA9685 through the I²C-bus, identical to the Power-On Reset (POR) that initializes the
registers to their default state causing the outputs to be set LOW. This allows an easy and
quick way to reconfigure all device registers to the same condition via software.