ICLS6022J Datasheet, PDF (16/33 Pages) Infineon Technologies AG – LED System Driver ICs

LED System Driver ICs
ICLS6x Series
Functional Description
As a consequence of this extra charge stage, there is no delay at the beginning of the startup phase when there
is still no switching. Furthermore, soft start is finished at 3.2 V to have maximum power capability even earlier. The
duty cycles DC₁ and DC₂ vary according to the mains and the primary inductance of the transformer. The limitation
of the primary current by DC₂ is related to V_SoftS = 3.2 V. However, DC₁ is related to a maximum primary current,
which is limited by the internal current limiting function with CS = 1 V. Therefore the maximum startup phase is
divided into a soft start phase until t1 and a phase from t1 to t2 during which maximum power is provided if
demanded by the FB signal.
3.4
PWM Section
Oscillator
Duty
Cycle
max
Clock
Frequency
Jitter
Soft Start
Comparator
PWM
Comparator
Current
Limiting
0.75
PWM Section
FF1
1
S
Gate Driver
G8
RQ
&
G9
Figure 8 PWM section
SoftS
Gate
3.4.1 Oscillator and Jittering
The oscillator generates a fixed frequency with frequency jittering of ± 4 % from the fixed frequency (i.e., ± 2.7 kHz
for 67 kHz) at a jittering period T_FJ. The switching frequency is f_switch = 67 kHz.
A resistor, a capacitor, a current source and current sink for determining the frequency are integrated. The
charging and discharging current of the implemented oscillator capacitor are internally trimmed in order to achieve
a very accurate switching frequency. The ratio of controlled charge to discharge current is adjusted to reach a
maximum duty cycle limitation of D_max = 0.75.
Once the soft start period is over and the IC has entered normal mode, the soft start capacitor is charged and
discharged through the internal current source I_FJ to generate a triangular waveform with a jittering period T_FJ,
which is externally adjustable by means of the soft start capacitor, C_SoftS (see Figure 6).
T_FJ = k_FJ ∗ C_SoftS
(1)
where k_FJ is a constant = 4 ms/µF.
For example: T_FJ = 4 ms if C_SoftS = 1µF.
Data Sheet
16
Version 1.0, 2011-05-19