ICE3BR2280JZ Datasheet, PDF (15/34 Pages) Infineon Technologies AG – Off-Line SMPS Current Mode Controller with integrated 800V

CoolSET^®-F3R80
ICE3BR2280JZ
Functional Description
switches off the switch S1 and turns on the switch S2.
The voltage at BBA pin will be discharged through a
500W resistor. When the voltage drops to 0.9V which is
sensed by comparator C3, the switch S2 will be turned
off and the switch S1 will be turned on. Then the
constant current I_{chg_EB} will charge the C_BK capacitor
again. When the voltage at BBA hits 4.5V which is
sensed by comparator C11, the counter will increase
the count to 2. The process repeats until it reaches total
count of 256 (Figure 23). Then the counter will release
a high output signal. When the AND gate G5 detects
both high signals at the inputs, it will activate the 30ms
spike blanking circuit and finally the auto-restart mode
will be activated.
V_BBA
256 counts
4.5V
Most of the burst mode design in the market will
provide a fixed entry burst mode level which is a ratio
to the maximum power of the design. F3R80 provides
a more flexible level which can be selected externally.
The provision also includes not entering burst mode.
Propagation delay is the major contributor for the
power control variation for DCM flyback converter. It is
proved to be effective in the maximum power control.
F3R80 also apply the same concept in the burst mode.
Therefore, the entry and exit burst mode power is also
finely controlled during burst mode.
The feedback control swing during burst mode will
affect the output ripple voltage directly. F3R80 reduces
the swing from 0.5V to 0.3V. Therefore, it would have
around 40% improvement for the output ripple.
CS
V_{csth_burst} C12
G10 & FF1
Current Limiting
normal _0.9V
operation _{extended blanking time}
auto
restart
Figure 23 Waveform at extended blanking time
For example, if C_BK=0.1mF, I_{chg_EB}=720mA
Extended blanking time = 256*(C_BK*(4.5V-0.9V)/I_{chg_EB} +
C_BK*500*ln(4.5/0.9)) = 148.6ms
Total blanking time = 20ms+ 148.6ms =168.6ms
If there is a resistor R_BO2 connected to BBA pin, the
effective charging current will be reduced. The blanking
time will be increased.
For example, if C_BK=0.1mF, I_{chg_EB}=720mA, R_BO2=12.8KW,
I_{chg_EB}’=I_{chg_EB}-(4.5V+0.9V)/(2*R_BO2)=509 mA
Extended blanking time = 256*(C_BK*(4.5V-0.9V)/I_{chg_EB}’ +
C_BK*500*ln(4.5/0.9)) = 201.6ms
Total blanking time = 20ms+201.6 = 221.6ms
where I_{chg_EB}’=net charging current to C_BK
Note: The above calculation does not include the effect of the
brownout circuit where there is extra biasing current flowing from
the input. That means the extended blanking time will be
shortened with the line voltage change if brownout circuit is
implemented.
3.7.2
Active Burst Mode (patented)
To increase the efficiency of the system at light load,
the most effective way is to operate at burst mode.
Starting from CoolSET^® F3, the IC has been employing
the active burst mode and it can achieve the lowest
standby power. F3R80 adopts the same concept with
some more innovative improvements to the feature. It
includes the adjustable entry burst level, close power
control between high line and low line and the smaller
output ripple during burst mode.
Burst detect
and adjust
V_{FB_burst C5}
FBB
C_FB
C13
4.0V
3.5V
C6a
Internal
Bias
20ms Blanking
Time
Active Burst
Mode
C6b
3.2V
&
G11
Control Unit
Figure 24 Active Burst Mode
The Active Burst Mode is located in the Control Unit.
Figure 24 shows the related components.
3.7.2.1 Selectable burst entry level
The burst mode entry level can be selected by
changing the different capacitor C_FB at FBB pin. There
are 4 levels to be selected with different capacitor
which are targeted for 10%, 6.67%, 4.38% and 0% of
the maximum input power. At the same time, the exit
burst level are targeted to 20%, 13.3%, 9.6% and 0%
of the maximum power accordingly. The corresponding
capacitance range is from 6.8nF to 100pF. The below
table is the recommended capacitance range for the
entry and exit level with the C_FB capacitor.
Version 2.1a
15
11 Jan 2012