F3 PWM controller
ICE3BS03LJG
Functional Description
The Propagation Delay Compensation is realized by blanking time is passed, the switch S1 is opened by
means of a dynamic threshold voltage Vcsth (see Figure G2. Then the 0.9V clamped voltage at BL pin is
21). In case of a steeper slope the switch off of the charged to 4.0V through the internal IBK constant
driver is earlier to compensate the delay.
current. Then G5 is enabled by comparator C3. After
the 30us spike blanking time, the Auto Restart Mode is
activated.
3.7
Control Unit
For example, if CBK = 0.22uF, IBK = 13uA
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.
Blanking time = 20ms + CBK x (4.0 - 0.9) / IBK = 72ms
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 VOUT 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.
3.7.1
Basic and Extendable Blanking Mode
BL
CBK
5.0V
#
IBK
Soft Start
block
0.9V
C3
1
S1
G2
Internal Bias
Current
Limiting
&
20 ms Blanking
Time
Spike
Blanking
30us
4.0V
G10
&
4.0V
C4
20ms
Blanking
Time
G5
Auto
Restart
Mode
4.0V
C4
C5
Active
FB
Burst
Mode
C5
&
G6
1.23V
3.5V
3.0V
&
Active
Burst
Mode
FB
20ms
Blanking
Time
G6
1.23V
C6a
C6b
Control Unit
&
G11
Figure 22
Basic and Extendable Blanking Mode
Control Unit
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 CBK is added to BL pin. While the 20ms
Figure 23
Active Burst Mode
The Active Burst Mode is located in the Control Unit.
Figure 23 shows the related components.
Version 2.0
14
6 Dec 2007
INFINEON [ Infineon ]
