VIPER26 STMicroelectronics, VIPER26 Datasheet - Page 15

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VIPER26

Manufacturer Part Number
VIPER26
Description
VIPerPlus family: fixed frequency high performance off line high voltage converter
Manufacturer
STMicroelectronics
Datasheet

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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
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
When the power supply output voltage is equal to the error amplifier reference voltage,
V
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.
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
parallel with the compensation network. The V
and V
When the voltage V
burst mode, see
When the voltage V
reach its limit, as well as the deliverable output power
Figure 23. Feedback circuit
REF_FB
15. The current loop has to be closed on the COMP pin through the opto-transistor in
COMPH
and the
Table 8 on page
, a single resistor has to be connected from the output to the FB pin. For higher
R
R
H
L
V
OUT
as reported on
No
Isolation
Figure 23 on page
Figure 23 on page
Section 13 on page
COMP
COMP
7.
Isolation
drops below the voltage threshold V
rises above the V
Figure 24 on page
Doc ID 17736 Rev 2
FB
Without Isolation:
switch open & E/A enabled
With Isolation:
switch closed & E/A disabled
15, in case of isolated power supply, the internal error
15.
16.
V
REF_FB
-
COMPH
+
E/A
COMP
16.
COMP
V
REF
threshold, the peak drain current will
SW
R
COMP
dynamics ranges is between V
BUS
nR
from R
V
COMPL
COMPL
R
SENSE
COMP
+
+
-
-
, the converter enters
FB pin and COMP pin
, respectively to and
PWM stop
to PWM
Figure 23 on
Figure 2 on
REF_FB,
COMPL
15/25

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