Datasheet
CoolSET
®
-F3R
ICE3Bxx65J
Version 2.7 11 9 May 2012
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 14.4%. By means of
propagation delay compensation the overshoot is only
about 2% (see Figure 11).
Figure 11 Overcurrent Shutdown
The Propagation Delay Compensation is realized by
means of a dynamic threshold voltage V
csth
(see Figure
12). In case of a steeper slope the switch off of the
driver is earlier to compensate the delay.
Figure 12 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
Figure 13 Adjustable Blanking Window
V
SoftS
swings between 3.2V and 3.6V after the SMPS is
settled and S2 is on while S3 is off, this is due to the
frequency jittering function that is making use of the
Soft Start pin. If overload occurs V
FB
is exceeding 4.5V.
Auto Restart Mode can’t be entered as the gate G5 is
still blocked by the comparator C3. But after V
FB
has
0,9
0,95
1
1,05
1,1
1,15
1,2
1,25
1,3
0 0,2 0,4 0,6 0,8 1 1,2 1,4 1,6 1,8 2
with compensation without compensation
dt
dV
Sense
s
V
Sense
V
V
t
V
csth
V
OSC
Signal1 Signal2
V
Sense
Propagation Delay
max. Duty Cycle
off time
t
C3
4.0V
C4
4.5V
C5
1.35V
&
G5
&
G6
3.0V
S1
Control Unit
Active
Burst
Mode
Auto
Restart
Mode
R
SoftS
5V
SoftS
FB
Frequency
Jitter
S2
S3