Leaving Active Burst Mode - Infineon CoolSET-F3R ICE3BRXX65JZ series Design Manual

6.3.3

Leaving Active Burst Mode

When the output load increases to be higher than the maximum burst power, P
will rise up fast to exceed 4.0V. The system leaves burst mode immediately when V
system leaves burst mode, the current sense voltage limit, V
V swings back to the normal control level.
FB
The leaving burst power threshold (i.e. maximum power to be handled during burst operation) is expressed
in equation (6).
= ⋅ ⋅
P 0 5 . L ( . 0
burst _ max P
I
where, : maximum primary peak current, V
p _ max
input power
The calculated maximum power in burst mode is around 6.76% of P
higher as it would include propagation delay time.
The leave burst mode timing diagram is shown in Figure 10. The maximum output drop during the transition
can be estimated in equation (7).
R
=
V
out _ drop _ max ⋅
R G
FB
4.0V
3.5V
V
FB
3.0V
V
V
out out_AV
1.03V
V
0.34V
CS
Figure 10 Timing diagram of leaving burst mode
Figure 11 is the captured waveform when there is a load jump from light load to full load. The output ripple
drop during the transition is about 88mV.
V
o
88mV
V
FB
V
CS
Figure 11 Leaving burst mode waveform
Application Note
⋅ 2 ⋅ =
34 I ) f
p _ max SW
+
3 3 5 .
opto ⋅ −
4 (
⋅
G 2
opto TL 431
V
out_drop_max
, is released to 1V, the feedback voltage
CS_MAX
V
CS _ max
⋅ ⋅ ⋅
0 5 . L ( . 0 34
P
R
sense
: current limit threshold at CS pin, P
CS_max
in_max
⋅
. 0 75 R
= opto
)
⋅ ⋅
R G G
FB opto TL 431
Channel 1; C1 : CS Voltage (V
Channel 2; C2 : Output Voltage (V
Channel 3; C3 : FB voltage (V
Leaving Active Burst mode when load change from
light to full @ Vin=85Vac
12
ICE3BRXX65J(Z)(G)
, V will drop and V
burst_max out
reaches 4.0V. Once
FB
2 ⋅ = ⋅
) f . 0 1156 P
SW in _
in_max
. However, the actual power can be
)
CS
)
o
)
FB
FB
(6)
max
: maximum
(7)
2010-06-20