VIPER15 STMicroelectronics, VIPER15 Datasheet - Page 29

• Manufacturer Part Number: VIPER15
• Description: VIPerPlus family: quasi-resonant high performance off line high voltage converter
• Manufacturer: STMicroelectronics

VIPER15
The time, from the high load detection, V
depends from the value of the capacitor C
OLP delay time can be calculating by the formula:
Equation 8
The current, I
also a part of the compensation loop , so they have to be selected taking into account the
proper delay and loop stability consideration. The
page 30
In the
circuit to compensate the feedback loop but also as element to delay the OLP shut down
owing to the time needed to charge the capacitor (see the
After the start-up time, t
capacitor could not be at its nominal value and the controller interpreter this situation as an
overload condition. In this case, the OLP delay helps to avoid an incorrect device shut down
during the start-up. See the relevant
Owing to the above considerations, the OLP delay time must be long enough to by-pass the
initial output voltage transient and check the overload condition only when the output voltage
is in steady state. The output transient time depends from the value of the output capacitor
and from the load.
When the value of the C
ensure enough OLP delay, an alternative compensation network can be used and it is
showed in
Using this alternative compensation network, two poles (f
introduced by the capacitors C
The capacitor C
is usually used to compensate the high frequency zero due to the ESR (Equivalent Series
Resistor) of the output capacitance of the fly-back converter.
The mathematical expressions of these poles and zero frequency, considering the scheme
in
Equation 9
Equation 10
Figure 35 on page 30
Figure 33 on page 27
show two different feedback networks.
Figure 35 on page 30
FB,
FB
is 3 μA as minimum value. The components connected to the FB pin are
introduces a pole (f
SU
FB
are reported by the equations below:
, during which the feedback voltage is fixed at V
capacitor calculated for the loop stability is too low and cannot
, the capacitor, C
T
f
PFB
OLP delay
Doc ID 15455 Rev 5
FB
.
and C
=
–
f
ZFB
2
Section 7.3 on page 16
⋅
PFB
⋅ π
FB1
=
=
FB
2
R
) at higher frequency than f
C
FB
C
FB
⋅
FB
and the resistor R
= V
⋅ π
FB
FB
(
and from the internal charge current, I
DYN
⋅
C
(
×
FBlin
, connected to FB pin is used as part of the
R
FB
1
V
--------------------------------------- -
)
FB
1
Figure 34 on page 30
+
FBolp
(
⋅
, to the overload turn-off, V
DYN
R
R
FB
FB
3μA
)
1
–
1
⋅
V
PFB
R
FBlin
FB
Equation 8
.
, f
1
FB1
)
PFB1
.
) and one zero (f
Operation description
ZB
).
and f
and
FBlin
PFB1
Figure 35 on
, the output
FB
. This pole
= V
FB
ZFB
FBolp
. The
) are
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,