CoolSET®-F3R
ICE3BR0665JF
Functional Description
3.6.1
Leading Edge Blanking
For example, Ipeak = 0.5A with RSense = 2. The current
sense threshold is set to a static voltage level Vcsth=1V
without Propagation Delay Compensation. A current
ramp of dI/dt = 0.4A/µs, or dVSense/dt = 0.8V/µs, and a
propagation delay time of tPropagation Delay =180ns leads
to an Ipeak overshoot of 14.4%. With the propagation
delay compensation, the overshoot is only around 2%
(see Figure 20).
VSense
Vcsth
tLEB = 220ns
with compensation
without compensation
V
1,3
1,25
1,2
t
Figure 18
Leading Edge Blanking
1,15
1,1
Whenever the internal CoolMOS® is switched on, a
leading edge spike is generated due to the primary-
side capacitances and reverse recovery time of the
secondary-side rectifier. This spike can cause the gate
drive to switch off unintentionally. In order to avoid a
premature termination of the switching pulse, this spike
is blanked out with a time constant of tLEB = 220ns.
1,05
1
0,95
0,9
0
0,2
0,4
0,6
0,8
1
1,2
1,4
1,6
1,8
2
V
dVSense
dt
µs
3.6.2
Propagation Delay Compensation
Figure 20
Overcurrent Shutdown
In case of overcurrent detection, there is always
propagation delay to switch off the internal CoolMOS®.
An overshoot of the peak current Ipeak is induced to the
delay, which depends on the ratio of dI/dt of the peak
current (see Figure 19).
The Propagation Delay Compensation is realized by
means of a dynamic threshold voltage Vcsth (see Figure
21). In case of a steeper slope the switch off of the
driver is earlier to compensate the delay.
VOSC
max. Duty Cycle
Signal2
IOvershoot2
Signal1
tPropagation Delay
ISense
Ipeak2
Ipeak1
ILimit
off time
VSense
Vcsth
t
Propagation Delay
IOvershoot1
t
Figure 19
Current Limiting
Signal1
Signal2
The overshoot of Signal2 is larger than of Signal1 due
to the steeper rising waveform. This change in the
slope is depending on the AC input voltage.
Propagation Delay Compensation is integrated to
reduce the overshoot due to dI/dt of the rising primary
current. Thus the propagation delay time between
exceeding the current sense threshold Vcsth and the
switching off of the integrated CoolMOS® is
compensated over temperature within a wide range.
Current Limiting is then very accurate.
t
Figure 21
Dynamic Voltage Threshold Vcsth
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
Version 2.0
14
11 Sep 2008
INFINEON [ Infineon ]
