VIPER17_0810 STMICROELECTRONICS [STMicroelectronics], VIPER17_0810 Datasheet - Page 18

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

Operation descriptions
7.4
7.5
7.6
18/33
Power down operation
At converter power down, the system loses regulation as soon as the input voltage is so low
that the peak current limitation is reached. The V
the V
to the IC interrupted and consequently the V
Later, if the V
and the power down completed. This feature is useful to prevent converter’s restart attempts
and ensures monotonic output voltage decay during the system power down.
Auto restart operation
If after a converter power down, the V
is not inhibited and will be activated only when the V
threshold (4.5 V typical). This means that the HV start up current generator restarts the V
capacitor charging only when the V
described is for instance a power down because of a fault condition. After a fault condition,
the charging current is 0.6 mA (typ.) instead of the 3 mA (typ.) of a normal start up converter
phase. This feature together with the low V
fault, the restart attempts of the IC has a very long repetition rate and the converter works
safely with extremely low power throughput. The
short circuit event.
Figure 25. Timing diagram: behavior after short circuit
Oscillator
The switching frequency is internally fixed to 60 kHz or 115 kHz. In both case the switching
frequency is modulated by approximately ±4 kHz (60 kHz version) or ±8 kHz
(115 kHz version) at 250 Hz (typical) rate, so that the resulting spread-spectrum action
distributes the energy of each harmonic of the switching frequency over a number of side-
band harmonics having the same energy on the whole but smaller amplitudes.
DDoff
FB Pin
FB Pin
IDD_CH
threshold (8 V typical) the power MOSFET is switched OFF, the energy transfers
VDS
VDS
I
I
V
V
V
V
V
V
DD_CH
DD_CH
V
V
DD
DD
0.6 mA
0.6 mA
DDrest
DDrest
DD
DD
DD
DD
4.8 V
4.8 V
3.3 V
3.3 V
OFF
OFF
IN
ON
ON
is lower than V
DRAIN_START
Short circuit occurs here
Short circuit occurs here
DD
IN
voltage drops below V
is higher than V
DDrestart
(80 V typical), the start up sequence is inhibited
DD
voltages decreases,
DD
Figure 25
< 0.03T
< 0.03T
threshold (4.5 V) ensures that, after a
voltage drops and when it falls below
DD
T
T
rep
rep
rep
rep
voltage drops down the V
DRAIN_START,
shows the IC behavioral after a
DDrestart
Figure 23 on page
. The scenario above
the start up sequence
DDrestart
VIPER17
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t
t
t
t
t
t
t
t
t
17.
DD