VIPER27LN STMicroelectronics, VIPER27LN Datasheet - Page 15

• Manufacturer Part Number: VIPER27LN
• Description: IC OFFLINE CONV PWM OVP 8DIP
• Manufacturer: STMicroelectronics
• Series: VIPer™ plusr

Specifications of VIPER27LN

• Output Isolation: Isolated
• Frequency Range: 54 ~ 66kHz
• Voltage - Input: 8.5 ~ 23.5 V
• Voltage - Output: 800V
• Power (watts): 24W
• Operating Temperature: -40°C ~ 150°C
• Package / Case: 8-DIP (0.300", 7.62mm), 7 Leads
• Output Voltage: 800 V
• Output Power: 1 W
• Input Voltage: - 0.3 V
• Switching Frequency: 115 KHz
• Operating Temperature Range: - 40 C to + 150 C
• Mounting Style: Through Hole
• Duty Cycle (max): 80 %
• Number Of Outputs: 1
• For Use With: 497-9084 - EVAL BOARD FOR VIPER27LX
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 497-8390-5

VIPER27
7.3
Power-up and soft-start up
If the input voltage rises up till the device start threshold, V
begins to grow due to the I
high voltage start up circuit. If the V
page 6
See
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. I
VDD
Figure 23 on page 16
SSaux
capacitor must be sized enough to avoid fast discharge and keep the needed voltage
) the power MOSFET starts switching and the HV current generator is turned OFF.
is the time needed for the steady state of the auxiliary voltage. This time is
I
DDch
DD
V
(-3 mA)
DRAIN
V
V
V
V
V
current during start-up and burst mode
V
FBbm
DDon
DDoff
V
FBolp
FBlin
I
I
I
DD
DD1
DD0
DD
START- UP
FB
DDoff
threshold. In fact, a too low capacitance value could terminate the
.
DDch
NORMAL MODE
Doc ID 15133 Rev 5
current (see
C
DD
VDD
voltage reaches V
=
----------------------------------------
V
I
DD
DDch
DDon
Table 7 on page 6
capacitor calculation:
×
–
BURST MODE
t
V
SSaux
DDoff
DDon
DRAIN_START
threshold (see
) coming from the internal
Operation descriptions
, the V
NORMAL MODE
VDD
t
t
t
t
V
FBbmhys
Table 7 on
DD
, until when
voltage
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