VIPER27 STMicroelectronics, VIPER27 Datasheet - Page 17

• Manufacturer Part Number: VIPER27
• Description: VIPerPlus family: fixed frequency high performance off line high voltage converter
• Manufacturer: STMicroelectronics

VIPER27
7.4
7.5
7.6
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
energy transfers to the IC interrupted and consequently the V
Figure 23 on page 16
the start up sequence is inhibited 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
V
generator restarts the V
V
fault condition. After a fault condition, the charging current, I
the 3 mA (typ.) of a normal start up converter phase. This feature together with the low
V
long repetition rate and the converter works safely with extremely low power throughput.
The
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.
DD(RESTART)
DD(RESTART)
DD(RESTART)
Figure 25
DDoff
threshold (see
. The scenario above described is for instance a power down because of a
threshold (see
threshold ensures that, after a fault, the restart attempts of the IC has a very
shows the IC behavioral after a short circuit event.
. Later, if the V
DD
Table 7 on page 6
capacitor charging only when the V
Table 7 on page 6
Doc ID 15133 Rev 5
IN
IN
is lower than V
is higher than V
) the power MOSFET is switched OFF, the
). This means that the HV start up current
DD
voltage drops and when it falls below
DD
DRAIN_START
voltage drops down the
DRAIN_START,
DDch
DD
DD
, is 0.6 mA (typ.) instead of
voltages decreases,
voltage drops below
(see
Operation descriptions
the start up sequence
Table 7 on page 6
17/31
),