VIPER26

Manufacturer Part NumberVIPER26
DescriptionVIPerPlus family: fixed frequency high performance off line high voltage converter
ManufacturerSTMicroelectronics
VIPER26 datasheet
 
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VIPER26
12
FB pin and COMP pin
The device can be used both in non-isolated and in isolated topology. In case of non-
isolated topology, the feedback signal from the output voltage is applied directly to the FB
pin as inverting input of the internal error amplifier having the reference voltage, V
Table 8 on page
see the
The output of the error amplifier sources and sinks the current, I
from the compensation network connected on the COMP pin. This signal is then compared,
in the PWM comparator, with the signal coming from the SenseFET; the power MOSFET is
switched off when the two values are the same on cycle by cycle basis. See the
page 3
Figure 23 on page
and the
When the power supply output voltage is equal to the error amplifier reference voltage,
V
, a single resistor has to be connected from the output to the FB pin. For higher
REF_FB
output voltages the external resistor divider is needed. If the voltage on FB pin is
accidentally left floating, an internal pull-up protects the controller.
The output of the error amplifier is externally accessible through the COMP pin and it’s used
for the loop compensation: usually an RC network.
Figure 23 on page
As reported on
amplifier has to be disabled (FB pin shorted to GND). In this case an internal resistor is
connected between an internal reference voltage and the COMP pin, see the
page
15. The current loop has to be closed on the COMP pin through the opto-transistor in
parallel with the compensation network. The V
and V
as reported on
COMPH
When the voltage V
Section 13 on page
burst mode, see
When the voltage V
reach its limit, as well as the deliverable output power
Figure 23. Feedback circuit
V
OUT
R
H
No
R
Isolation
L
7.
15.
15, in case of isolated power supply, the internal error
COMP
Figure 24 on page
16.
drops below the voltage threshold V
COMP
16.
rises above the V
COMP
COMPH
Without Isolation:
V
switch open & E/A enabled
With Isolation:
switch closed & E/A disabled
FB
-
E/A
V
+
REF_FB
Isolation
COMP
Doc ID 17736 Rev 2
FB pin and COMP pin
, respectively to and
COMP
Figure 2 on
Figure 23 on
dynamics ranges is between V
, the converter enters
COMPL
threshold, the peak drain current will
REF
R
V
COMP
COMPL
PWM stop
+
-
SW
BUS
from R
SENSE
to PWM
+
nR
-
R
REF_FB,
COMPL
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