NIS6111
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6
OPERATING DESCRIPTION
Introduction
The BERS rectifier offers a new concept in rectification
for low voltage, high current outputs. This product
combines a high speed integrated circuit with a power
MOSFET, to create a device with speeds better than an
ultrafast silicon rectifier, and a forward drop that is less than
that of a Schottky diode.
This device is specifically designed for the low voltage
outputs required by today’s digital circuits. Current digital
products operate on voltages of less than 5.0 V and currents
in the tens to hundreds of amperes. BERS can greatly
increase the efficiency of low voltage, high current
converters, by reducing the rectifier drop to several
hundred millivolts.
This device consists of four major circuits as well as a
capacitor. BERS contains a power supply to regulate the
voltage on the bias supply cap, a high speed comparator to
sense the conduction state of the device, a high speed
driver, a power FET and a capacitor.
Bias Supply
The internal bias supply is a high current, switching
regulator. It will maintain a regulated voltage on the
internal capacitor as long as sufficient voltage is available
at the Reg In pin. When this pin is high, a current limited
switch allows current to charge the capacitor. When the
maximum charge voltage is reached, the switch is turned
off. If there is not sufficient reverse voltage to maintain a
5.0 V charge on the capacitor, the bias supply will charge
it to within 1.0 V of the reverse voltage.
The Regulator Input pin can be connected to the cathode
and will recharge the internal capacitor when the BERS is
reversed biased. This input requires a minimum voltage of
4.7 V to operate. In some cases this amount of reverse
voltage may not be available. When this is the case, the
Reg In pin can be connected to a higher voltage source. It
is not necessary that this source be synchronous with the
cathode voltage.
The Reg In voltage should not be allowed to go more
negative than the anode of the device. If this scenario can
occur, a small switching diode should be placed in series
with the Reg In pin.
Comparator/Driver
The polarity comparator is a medium gain, ultra high
speed design. It is integrated with the driver circuit, to
optimize the switching speed of the device. The
comparator input has a low offset voltage which biases the
inverting input several millivolts above ground. This is to
assure that at zero (or very low) current levels, the device
is off.
Figure 12. Detailed Block Diagram
+
-
Cap Power Supply
Reg In
-
+
UVLO
Cathode
FETComparator and Driver
Bias