ICL8001G Datasheet, PDF (9/16 Pages) Infineon Technologies AG – Single-Stage Flyback And PFC Controller For LED Lighting Applications

Single-Stage Flyback and PFC Controller
ICL8001G
Functional Description
required maximum V_CS versus various input bus
voltage can be calculated, which is shown in Figure 5.
1
0.9
0.8
0.7
0.6
80 100 120 140 160 180 200 220 240 260 280 300 320 340 360 380 400
Vin(V)
Figure 5 Variation of the VCS limit voltage according
to the IZC current
According to the typical application circuit, when
MOSFET is turned on, a negative voltage proportional
to bus voltage will be coupled to auxiliary winding.
Inside ICL8001G, an internal circuit will clamp the
voltage on ZC pin to nearly 0V. As a result, the current
flowing out from ZC pin can be calculated as
IZC
=
-V----B-----U----S----N-----a-
RZC1NP
[5]
When this current is higher than I_{ZC_1}, the amount of
current exceeding this threshold is used to generate an
offset to decrease the maximum limit on V_CS. Since the
ideal curve shown in Figure 5 is a nonlinear one, a
digital block in ICL8001G is implemented to get a better
control of maximum output power. Additional
advantage to use digital circuit is the production
tolerance is smaller compared to analog solutions. The
typical maximum limit on V_CS versus the ZC current is
shown in Figure 6.
1
3.5
Protection Functions
The IC provides full protection functions. The following
table summarizes these protection functions.
Table 1 Protection features
VCC Overvoltage
Auto Restart Mode
VCC Undervoltage
Auto Restart Mode
Over temperature
Auto Restart Mode
Output Overvoltage
Latched Off Mode
Short Winding
Latched Off Mode
During operation, the VCC voltage is continuously
monitored. In case of an under- or an over-voltage, the
IC is reset and the main power switch is then kept off.
After the VCC voltage falls below the threshold V_VCCoff,
the startup cell is activated. The VCC capacitor is then
charged up. Once the voltage exceeds the threshold
V_VCCon, the IC begins to operate with a new soft-start.
During off-time of the power switch, the voltage at the
zero-crossing pin is monitored for output over-voltage
detection. If the voltage is higher than the preset
threshold v_ZCOVP, the IC is latched off after the preset
blanking time.
If the junction temperature of IC exceeds 140 ⁰C, the IC
enter into autorestart mode.
If the voltage at the current sensing pin is higher than
the preset threshold v_CSSW during on-time of the power
switch, the IC is latched off. This is short-winding
protection.
During latch-off protection mode, when the VCC
voltage drops to 10.5V,the startup cell is activated and
the VCC voltage is charged to 18V then the startup cell
is shut down again and repeats the previous procedure.
There is also a maximum on time limitation inside
ICL8001G. Once the gate voltage is high longer than
t_OnMAx, it is turned off immediately.
0.9
0.8
0.7
0.6
300
500
700
900 1100 1300 1500 1700 1900 2100
Iz c(uA)
Figure 6
V_CS-max versus I_ZC
i
Version 1.0
9
May 6, 2010