Specifications

POWER
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THERMAL
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INTEGRATION
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OPTICAL
4
Achieving consistent colour
performance with LED
design requires a complex
set of calculations to
account for a variety of
factors, such as LED bin information and colour
shift over temperature. The EZ-Color LED controller
family from Cypress Semiconductor, supported by
the PSoC Express™ embedded visual design tool,
allows engineers to produce a complete design
solution simply by inputting the selected LEDs and
choosing a desired colour.
With PSoC Express, when
designers select a colour
from a range presented
on-screen, pre-loaded
manufacturers’
specifications and
temperature feedback
algorithms are
automatically applied to
the selected design,
reducing development
time. The EZ-Color
controller supports up to
16 independent LED
channels with up to 32
bits of resolution per
channel, enabling lighting
designers to select LED
array size and colour
quality.
The controller also
offers dynamic colour mixing that makes all colours within the
system range accessible instead of just the pre-set colours.
The dynamic colour-mixing feature also enables the system
to use feedback loops to maintain the set colour output
across temperature. Because a High Brightness (HB) LED’s
dominant wavelength, luminosity and forward voltage are all
dependent on junction temperature, HB LED temperature
feedback is critical for control. When the HB LED is enabled,
the junction temperature increases. As a result, the
wavelength increases whilst forward voltage and luminosity
decrease. This produces a challenge when trying to maintain
a stable colour point, since the system will be using out-
dated HB LED characteristics.
The simplest method of controlling the effect of temperature
on the HP LED system is through a temperature feedback loop.
The temperature feedback loop will use an approximation of the
LED controller family
quick and easy
offers
HB LED’s junction temperature using the board temperature,
the power of the HB LED and the thermal impedance from
junction to board (supplied by the HB LED manufacturer).
Temperature feedback loops are simple to implement using
the EZ-Color solution. EZ-Color devices can control both
digital and analogue signals enabling quick use of devices
such as temperature sensors (thermistors), analogue to
digital converters and amplifiers. PSoC Express provides
temperature compensation algorithms enabling the EZ-Color
devices to maintain the correct system colour output across
temperature. These algorithms update the controllers to
account for current HB LED characteristics.
Dimming control or current control of the HB LED is
another challenge EZ-Color devices address. Possible
designs for current control can involve a PWM or expensive
external ICs with external resistor control. The PWM method
can dynamically change the brightness through its duty
cycle for colour mixing and tends to be a more efficient
solution because of its flexibility. The EZ-Color solution can
support up to 16 independently-controlled HB LEDs using
the PWM method.
Typical difficulties of using a PWM include high EMI and
inherently low frequency flicker. Cypress has addressed
these issues with
PrISM™ (Precise
Illumination Signal
Modulation)
technology, which uses
a spread-spectrum
dimming waveform
with user-defined signal
density to deliver
consistent colour in
varied conditions.
The CY8CLEDxx
EZ-Color family
includes devices that
drive up to four, eight
or sixteen LEDs, in
applications such as
architectural lighting,
signage, backlighting,
handset flash and
torches.
The EZ-Color controller family from Cypress
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colour mixing
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