CoolSET®-F3R
ICE3BR4765J
Functional Description
After the 30us spike blanking time, the Auto Restart
Mode is activated.
3.7
Control Unit
The Control Unit contains the functions for Active Burst
Mode and Auto Restart 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 BA 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.
For example, if CBK = 0.22uF, IBK = 13uA
Blanking time = 20ms + CBK x (4.0 - 0.9) / IBK = 72ms
In order to make the startup properly, the maximum CBK
capacitor is restricted to less than 0.65uF.
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
BA
5.0V
CBK
#
IBK
0.9V
1
S1
G2
Internal Bias
Current
C3
Spike
Blanking
30us
4.0V
4.0V
Limiting
20 ms Blanking
Time
&
G10
&
4.0V
20ms
Blanking
Time
G5
Auto
Restart
Mode
C4
C4
Active
Burst
Mode
FB
C5
&
FB
&
Active
Burst
Mode
1.35V
3.5V
3.0V
20ms
Blanking
Time
G6
C5
G6
1.35V
C6a
C6b
Control Unit
&
Figure 22
Basic and Extendable Blanking Mode
G11
There are 2 kinds of Blanking mode; basic mode and
the extendable mode. The basic mode is just an
internal set 20ms blanking time while the extendable
mode has an extra blanking time by connecting an
external capacitor to the BA pin in addition to the pre-
set 20ms blanking time. 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 BA
pin. While the 20ms blanking time is passed, the switch
S1 is opened by G2. Then the 0.9V clamped voltage at
BA pin is charged to 4.0V through the internal IBK
constant current. G5 is enabled by comparator C3.
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 C5.
During normal operation, the internal blanking time
counter is reset to 0. Once the FB signal falls below
1.35V, it starts to count. When the counter reach 20ms
Version 2.5
15
19 Nov 2012
INFINEON [ Infineon ]
