CS1630 Datasheet, PDF (14/56 Pages) Cirrus Logic – 2-Channel TRIAC Dimmable LED Driver IC

CS1630/31
dim
ADC
NTC
Iref
White
Gain
White
Iref
Color
Gain
Color
X
IWhite
X
X
X
IColor
Figure 11. Block Diagram of Color Control System
The reference currents are the required values at T_A = 25ºC
and dim = 100%. They are multiplied by the appropriate gains,
and these values are passed to the final power stage. The
CS1630/31 uses polynomial approximations in one and two
dimensions to generate the color gains. These polynomials
can be up to third-order.
GAIN_DTR approximations create a custom temperature
compensation profile and dimming profile of the temperature-
sensitive LEDs (see Equation 1). Profiles are programmed
through the Color Polynomial Coefficient registers (see "Color
Polynomial Coefficient (P30, P20, P10, P03, P02, P01, P21,
P12, P11, P00) – Address 5 - 24" on page 29).
GAIN_DR approximation allows custom dimming profile of the
white LEDs (see Equation 2). The profile is programmed
through the Color Polynomial Coefficient registers (see "Color
Polynomial Coefficient (Q3, Q2, Q1, Q0) – Address 25 - 32" on
page 30).
Cirrus Logic, Inc. and its affiliates and subsidiaries generally
make no representations or warranties that the combination of
Cirrus Logic’s products with light-emitting diodes (“LEDs”),
converter materials, and/or other components will not infringe
any third-party patents, including any patents related to color
mixing in LED lighting applications, such as, for example, U.S.
Patent No. 7,213,940 and related patents of Cree, Inc. For
more information, please see Cirrus Logic’s Terms and
Conditions of Sale, or contact a Cirrus Logic sales
representative.
5.5 Dimming Signal Extraction and the
Dim Mapping Algorithm
When operating with a dimmer, the dimming signal is
extracted in the time domain and is proportional to the
conduction angle of the dimmer. A control variable is passed
to the quasi-resonant second stage to achieve 0% to 100%
output currents.
5.6 Boost Stage
The high-voltage FET in the source-follower startup circuit is
source-switched by a variable current source on the SOURCE
pin to operate a boost circuit. Peak FET switching current is
set by the PEAK_CUR register (see "Peak Current
(PEAK_CUR) – Address 51" on page 39).
In No-dimmer Mode, the boost stage begins operating when
the start threshold is reached during each rectified half line-cy-
cle and is disabled at the nominal boost output voltage. The
peak FET switching current determines the percentage of the
rectified input voltage conduction angle over which the boost
stage will operate. The control algorithm adjusts the peak FET
switching current to maximize the operating time of the boost
stage, thus improving the input power factor.
When operating in Leading-edge Mode, the boost stage
ensures the hold current requirement of the dimmer is met
from the initiation of each half-line dimmer conduction cycle
until the peak of the rectified input voltage. Trailing-edge Mode
boost stage ensures that the trailing-edge is exposed at the
correct time with the correct current.
GAINDTR= P30  T3 + P20  T2 + P10  T + P03  D3 + P02  D2 + P01  D + P21  T2  D + P12  T  D2 + P11  T  D + P00 [Eq.1]
where,
T = the measured normalized temperature and is 0T1.0
D = the normalized dim value and is 0D1.0
GAIN_DTR = gain of the channel based on the temperature measurement and the dim value:
GAIN_DR = Q3  D³ + Q2  D² + Q1  D + Q0
[Eq. 2]
where,
D = the normalized dim value and is 0D1.0
GAIN_DR = gain of the channel based on the dim value
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