ICE3A1065ELJ Datasheet, PDF (15/29 Pages) Infineon Technologies AG – Off-Line SMPS Current Mode Controller with integrated 650V CoolMOS

CoolSET^®-F3
ICE3A1065ELJ
Functional Description
3.7
Control Unit
The Control Unit contains the functions for Active Burst
Mode, Auto Restart Mode and Latched Off Mode. The
Active Burst Mode and the Auto Restart Mode both
have 20ms internal Blanking Time. For the Auto
Restart Mode, a further extendable Blanking Time is
achieved by adding external capacitor at BL pin. By
means of this Blanking Time, the IC avoids entering
into these two modes accidentally. Furthermore those
buffer time for the overload detection is very useful for
the application that works in low current but requires a
short duration of high current occasionally.
3.7.1
Basic and Extendable Blanking Mode
BL
# ^CBK
I_BK
5.0V
0.9V
1
S1
G2
Soft Start
block
the 8.0us spike blanking time, the Auto Restart Mode is
activated.
For example, if C_BK = 0.22uF, I_BK = 8.4uA
Blanking time = 20ms + C_BK x (4.0 - 0.9) / I_BK = 100ms
The 20ms blanking time circuit after C4 is disabled by
the soft stat block such that the controller can start up
properly.
The Active Burst Mode has basic blanking mode only
while the Auto Restart Mode has both the basic and the
extendable blanking mode.
3.7.2
Active Burst Mode
The IC enters Active Burst Mode under low load
conditions. With the Active Burst Mode, the efficiency
increases significantly at light load conditions while still
maintaining a low ripple on V_OUT and a fast response on
load jumps. During Active Burst Mode, the IC is
controlled by the FB signal. Since the IC is always
active, it can be a very fast response to the quick
change at the FB signal. The Start up Cell is kept OFF
in order to minimize the power loss.
C3
4.0V
4.5V
C4
20ms
Blanking
Time
Spike
Blanking
8.0us
&
G5
Auto
Restart
Mode
4.5V
20 ms Blanking
Time
C4
Internal Bias
Current
Limiting
&
G10
FB
C5
1.35V
20ms
Blanking
Time
&
Active
G6
Burst
Mode
Control Unit
Figure 22 Basic and Extendable Blanking Mode
There are 2 kinds of Blanking mode; basic mode and
the extendable mode. The basic mode has an internal
pre-set 20ms blanking time while the extendable mode
has extended blanking time to basic mode by
connecting an external capacitor to the BL pin. For the
extendable mode, the gate G5 is blocked even though
the 20ms blanking time is reached if an external
capacitor C_BK is added to BL pin. While the 20ms
blanking time is passed, the switch S1 is opened by
G2. Then the 0.9V clamped voltage at BL pin is
charged to 4.0V through the internal I_BK constant
current. Then G5 is enabled by comparator C3. After
FB
C5
1.35V
Active
Burst
&
Mode
G6
C6a
3.61V
C6b
3.0V
&
G11
Control Unit
Figure 23 Active Burst Mode
The Active Burst Mode is located in the Control Unit.
Figure 23 shows the related components.
3.7.2.1 Entering Active Burst Mode
The FB signal is kept monitoring by the comparator C4.
During normal operation, the internal blanking time
counter is reset to 0. When FB signal falls below 1.35V,
Version 2.1
15
12 May 2009