ICE3AS02 Datasheet, PDF (12/23 Pages) Infineon Technologies AG – Off-Line SMPS Current Mode Controller with integrated 500V Startup Cell

F3
ICE3AS02 / ICE3AS02G / ICE3BS02 / ICE3BS02G
Functional Description
Current Limiting is now possible in a very accurate way.
E.g. I_peak = 0.5A with R_Sense = 2. Without Propagation
Delay Compensation the current sense threshold is set
to a static voltage level V_csth=1V. A current ramp of
dI/dt = 0.4A/µs, that means dV_Sense/dt = 0.8V/µs, and a
propagation delay time of i.e. t_{Propagation Delay} =180ns
leads then to an I_peak overshoot of 12%. By means of
propagation delay compensation the overshoot is only
about 2% (see Figure 13).
V
1,3
1,25
1,2
1,15
1,1
1,05
1
0,95
0,9
0
with compensation
without compensation
0,2 0,4 0,6 0,8
1 1,2 1,4 1,6 1,8
dV_Sense
dt
2V
µs
Figure 13 Overcurrent Shutdown
The Propagation Delay Compensation is realized by
means of a dynamic threshold voltage V_csth (see Figure
14). In case of a steeper slope the switch off of the
driver is earlier to compensate the delay.
V_{OSC max. Duty Cycle}
V_Sense
V_csth
off time
Propagation Delay
t
Figure 14
Signal1
Signal2
t
Dynamic Voltage Threshold V_csth
3.6
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 are combined with an
Adjustable Blanking Window which is depending on the
external Soft Start capacitor. By means of this
Adjustable Blanking Window, the IC avoids entering
into these two modes accidentally. Furthermore it also
provides a certain time whereby the overload detection
is delayed. This delay is useful for applications which
normally works with a low current and occasionally
require a short duration of high current.
3.6.1
Adjustable Blanking Window
SoftS
6.5V
5k ^RSoftS
4.4V
1
S1
G2
C3
5.4V
4.8V
C4
&
Auto
Restart
G5
Mode
Active
Burst
Mode
FB
C5
1.32V
&
G6
Control Unit
Figure 15 Adjustable Blanking Window
V_SoftS is clamped at 4.4V by the closed switch S1 after
the SMPS is settled. If overload occurs V_FB is
exceeding 4.8V. Auto Restart Mode can’t be entered as
the gate G5 is still blocked by the comparator C3. But
after V_FB has exceeded 4.8V the switch S1 is opened
via the gate G2. The external Soft Start capacitor can
Version 1.1
12
21 May 2004