VIPER17_0810 STMICROELECTRONICS [STMicroelectronics], VIPER17_0810 Datasheet - Page 16

• Manufacturer Part Number: VIPER17_0810
• Description: Off-line high voltage converters
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

Operation descriptions
7.3
16/33
Power-up and soft-start up
If the input voltage rises up till the device start level (V
to grow due to the IDD_ch current (see
voltage start up circuit. If the V
MOSFET starts switching and the HV current generator is turned OFF. See
page
The IC is powered by the energy stored in the capacitor on the VDD pin, C
the self-supply circuit (typically an auxiliary winding of the transformer and a steering diode)
develops a voltage high enough to sustain the operation.
C
value higher than V
switching operation before the controller receives any energy from the auxiliary winding.
The following formula can be used for the V
Equation 1
The t
estimated by applicator according to the output stage configurations (transformer, output
capacitances, etc.).
During the converter start up time, the drain current limitation is progressively increased to
the maximum value. In this way the stress on the secondary diode is considerably reduced.
It also helps to prevent transformer saturation. The soft-start time lasts 8.5 ms and the
feature is implemented for every attempt of start up converter or after a fault.
Figure 22. Start up I
VDD
SSaux
17.
capacitor must be sized enough to avoid fast discharge and keep the needed voltage
is the time needed for the steady state of the auxiliary voltage. This time is
I
DS_CH_FAULT
I
-3 mA
-1 mA
-2 mA
-4 mA
2 mA
DD_FAULT
1 mA
I
DD_OFF
I
DD
I
I
DS_CH
DD0
DDoff
V
DDrestart
DD
threshold. In fact, a too low capacitance value could terminate the
current
DD
V
voltage reaches V
DDoff
C
VDD
Table 7 on page
=
----------------------------------------
V
I
DD
DDch
DDon
V
capacitor calculation:
DDon
×
–
t
V
SSaux
DDoff
DDon
DRAIN_START
7) coming from the internal high
V
threshold (~14 V) the power
DD
V
F
), the V
SW
DS
= 120V
= 0 kHz
AFTER FAULT
DD
VDD
Figure 23 on
voltage begins
, until when
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