NXP – PCA9955A 16-Channel Fm+ I2C-Bus 57mA/20V Constant Current LED Driver

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Industrial or home automation system control panels use LEDs for status indicators and for LCD display backlighting. Elegant and userfriendly control panels are a snap to design and cost effective when built around new LED drivers ICs that do more than simply turn those LEDs on and off.

Controlling an LED directly ties up an MCU IO port pin. In addition, controlling the LED brightness through firmware PWM dimming also ties up the processor. When there’s more than just a couple of LEDs in your next user interface design add a dedicated LED driver IC. The latest LED driver from NXP (PCA9955A) requires only two IO port pins for control over the ubiquitous I2Cbus that’s built into most MCU ICs. Up to sixteen channels of LEDs can be controlled for ON-OFF or brightness (using PWM). These channels can also be assigned to groups for global dimming; ideal if your control panel is outdoors in both sunlight and moonlight.

A recent addition to these clever LED drivers is the ability to perform gradation – an automatic cycle that controls ramp up and ramp down of LED brightness. This is commonly used to indicate a sleep state when powered down, and only a tell-tale LED is seen ‘breathing’.

Registers in this LED driver are easily programmed with ‘ramp up’, ‘hold’, ’ramp down’ and ‘off’ durations, so that LED gradation (blinking and breathing) gives the system architect unique signaling options with no burden on the MCU overhead.

For backlighting with a string of LEDs this LED driver IC provides constant current (for better LED matching) and tolerates up to 20V for long strings of LEDs.

Each channel can sink over 50mA with no additional components needed, not even traditional LED ballast resistors. LEDs connect directly to this LED driver IC, which requires only a single global maximum current setting resistor.

More reliable end products result from this LED driver’s on-chip fault detector circuitry that reports both open and shorted LEDs.

Finally, with sixteen independently controlled channels, color mixing of RGB LED clusters opens your next control panel design up to end user customization.

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APPLICATIONS

  • Control panel UI LED status indicators
  • Internal service and troubleshooting LED indicators
  • “Breathing LED” stand-by indicators
  • LCD backlighting
  • Keypad backlighting
  • RGB or RGBA LED color mixing
  • Available in automotive grade (for harsh environments)
FeaturesBenefits
Gradation control for all channelsProgrammable LED “breathing” effect
High output drive up to 57mA per channelEliminates external FET
High output voltage up to 20V per channelDrive single or string of LEDs per channel
LED open or short error detectionReal-time LED monitoring
High resolution LED control (8-bit, 256 steps)Color mixing accuracy

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