3 Pin Description
VIPer50A-E/ASP-E
3
Pin Description
3.1
Drain Pin (Integrated Power MOSFET Drain):
Integrated Power MOSFET drain pin. It provides internal bias current during start-up via an
integrated high voltage current source which is switched off during normal operation. The
device is able to handle an unclamped current during its normal operation, assuring self
protection against voltage surges, PCB stray inductance, and allowing a snubberless operation
for low output power.
3.2
3.3
Source Pin:
Power MOSFET source pin. Primary side circuit common ground connection.
VDD Pin (Power Supply):
This pin provides two functions :
■
It corresponds to the low voltage supply of the control part of the circuit. If V goes below
DD
8V, the start-up current source is activated and the output power MOSFET is switched off
until the V voltage reaches 11V. During this phase, the internal current consumption is
DD
reduced, the V pin is sourcing a current of about 2mA and the COMP pin is shorted to
DD
ground. After that, the current source is shut down, and the device tries to start up by
switching again.
■
This pin is also connected to the error amplifier, in order to allow primary as well as
secondary regulation configurations. In case of primary regulation, an internal 13V
trimmed reference voltage is used to maintain V at 13V. For secondary regulation, a
DD
voltage between 8.5V and 12.5V will be put on V pin by transformer design, in order to
DD
stuck the output of the transconductance amplifier to the high state. The COMP pin
behaves as a constant current source, and can easily be connected to the output of an
optocoupler. Note that any overvoltage due to regulation loop failure is still detected by the
error amplifier through the V voltage, which cannot overpass 13V. The output voltage
DD
will be somewhat higher than the nominal one, but still under control.
3.4
Compensation Pin
This pin provides two functions :
■
It is the output of the error transconductance amplifier, and allows for the connection of a
compensation network to provide the desired transfer function of the regulation loop. Its
bandwidth can be easily adjusted to the needed value with usual components value. As
stated above, secondary regulation configurations are also implemented through the
COMP pin.
■
When the COMP voltage is going below 0.5V, the shut-down of the circuit occurs, with a
zero duty cycle for the power MOSFET. This feature can be used to switch off the
converter, and is automatically activated by the regulation loop (no matter what the
configuration is) to provide a burst mode operation in case of negligible output power or
open load condition.
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STMICROELECTRONICS [ ST ]
