Thermal Shut Down - Denon DRA-F107 Service Manual

But the Soft-Start Phase must be finished within the
Start Up Phase to force the voltage at pin FB below the
failure detection threshold of 4.8V.
3.8.2 Overvoltage due to Open Loop with
No Load
Open loop & no load condition
5μs Blanking
FB
4.8V
Failure
Detection
SoftS
5.3V
4.0V
Overvoltage
Detection Phase
Driver
VCC
16.5V
13.5V
8.5V
Figure 23 Auto Restart Mode
Figure 23 shows the Auto Restart Mode for open loop
and no load condition. In case of this failure mode the
converter output voltage increases and also VCC. An
additional protection by the comparators C1, C2 and
the AND-gate G1 is implemented to consider this
failure mode (see Figure 24).The overvoltage detection
is provided by Comparator C1 only in the first time
during the Soft-Start Phase till the Soft-Start voltage
exceeds the threshold of the Comparator C2 at 4.0V
and the voltage at pin FB is above 4.8V. When VCC
exceeds 16.5V during the overvoltage detection phase
C1 can set the Error-Latch and the Burst Phase during
Auto Restart Mode is finished earlier. In that case
T is shorter than T
Burst2
Soft-Start Phase
T
Burst2
T
Restart
Overvoltage Detection
. By means of C2 the
Soft-Start
DRA-F107 / DRA-F107DAB
normal operation mode is prevented from overvoltage
detection due to varying of VCC concerning the
regulation of the converter output. When the voltage
V is above 4.0V the overvoltage detection by C1 is
SoftS
deactivated.
VCC
6.5V
16.5V
R
Soft-Start
SoftS
t
C
Soft-Start
T1
Figure 24 Overvoltage Detection
t
3.8.3

Thermal Shut Down

Thermal Shut Down is latched by the Error-Latch when
junction temperature T
exceeding an internal threshold of 140°C. In that case
the IC switches in Auto Restart Mode.
t
t
Note: All the values which are mentioned in the
functional description are typical. Please refer
to Electrical Characteristics for min/max limit
values.
44
Functional Description
C1
G1
4.0V
C2
Power Up Reset
of the pwm controller is
j
Error Latch