Functional Description
Figure 20 Internal Gate Rising Slope
3.8 Protection Unit (Auto Restart Mode)
An overload, open loop and overvoltage detection is
integrated within the Protection Unit. These three
failure modes are latched by an Error-Latch. Additional
thermal shutdown is latched by the Error-Latch. In case
of those failure modes the Error-Latch is set after a
blanking time of 5μs and the CoolMOS™ is shut down.
That blanking prevents the Error-Latch from distortions
caused by spikes during operation mode.
3.8.1 Overload / Open Loop with Normal
Load
Figure 21 shows the Auto Restart Mode in case of
overload or open loop with normal load. The detection
of open loop or overload is provided by the Comparator
C3, C4 and the AND-gate G2 (see Figure 22). The
detection is activated by C4 when the voltage at pin
SoftS exceeds 5.3V. Till this time the IC operates in the
Soft-Start Phase. After this phase the comparator C3
can set the Error-Latch in case of open loop or overload
which leads the feedback voltage V
FB
to exceed the
threshold of 4.8V. After latching VCC decreases till
8.5V and inactivates the IC. At this time the external
Soft-Start capacitor is discharged by the internal
transistor T1 due to Power Down Reset. When the IC
is inactive V
VCC
increases till V
CCon
= 13.5V by charging
the Capacitor C
VCC
by means of the Start-Up Resistor
R
Start-Up
. Then the Error-Latch is reset by Power Up
Reset and the external Soft-Start capacitor C
Soft-Start
is
charged by the internal pull-up resistor R
Soft-Start
. During
the Soft-Start Phase which ends when the voltage at
pin SoftS exceeds 5.3V the detection of overload and
open loop by C3 and G2 is inactive. In this way the Start
Up Phase is not detected as an overload.
Figure 21 Auto Restart Mode
Figure 22 FB-Detection
t
V
Gate
5V
ca. t = 130ns
Overload / Open Loop with Normal Load
FB
t
4.8V
5.3V
SoftS
5μs Blanking
Failure
Detect ion
Soft-Start Phase
VCC
13.5V
8.5V
t
Driver
t
T
Restar t
T
Burst 1
t
R
Soft-Start
6.5V
C
Soft-Start
C4
5.3V
C3
4.8V
G2
T1
Error-Latch
Power Up Reset
R
FB
6.5V
FB
SoftS
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