PI3545-00-LGIZ Datasheet, PDF (32/37 Pages) Vicor Corporation – 36 Vin to 60 Vin Cool-Power ZVS Buck Regulator & LED Driver

VDR Bias Regulator
The VDR internal bias regulator is a ZVS switching regulator
that resides internal to the PI354x-00 product family. It is
intended strictly for use to power the internal controller and
driver circuitry. The power capability of this regulator is sized
only for the PI354x-00, with adequate reserve for the
application it was intended for. It may be used for as a pull-
up source for open collector applications and for other very
low power use with the following restrictions:
1. No direct connection is allowed. Any noise source that
can disturb the VDR voltage can also affect the internal
controller operation.
2. All loads must be locally de-coupled using a 0.1 μF
ceramic capacitor. This capacitor must be connected to
the VDR output through a series resistor no smaller than
1 k. which forms a loss pass filter and limits the total
current to 5 mA.
PI354x-00
System Design Considerations
1. Inductive loads- As with all power electronic applications,
consideration must be given to driving inductive loads
that may be exposed to a fault in the system which could
result in consequences beyond the scope of the power
supply primary protection mechanisms. An inductive
load could be a filter, fan motor or even excessively long
cables. Consider an instantaneous short circuit through
an un-damped inductance that occurs when the output
capacitors are already at an initial condition of fully
charged. The only thing that limits the current is the
inductance of the short circuit and any series resistance.
Even if the power supply is off at the time of the short
circuit, the current could ramp up in the external
inductor and store considerable energy. The release of this
energy will result in considerable ringing, with the
possibility of ringing nodes connected to the output
voltage below ground. The system designer should plan
for this by considering the use of other external circuit
protection such as load switches, fuses, and transient
voltage protectors. The inductive filters should be
critically damped to avoid excessive ringing or damaging
voltages. Adding a high current Schottky diode from the
output voltage to PGND close to the PI354x-00 is
recommended for these applications.
2. Low voltage operation – there is no isolation from an
SELV (Safety-Extra-Low-Voltage) power system. Powering
low voltage loads from input voltages as high as 60 V may
require additional consideration to protect low voltage
circuits from excessive voltage in the event of a short
circuit from input to output. A fast TVS (transient voltage
suppressor) gating an external load switch is an example
of such protection.
3. Use of Lighting Mode (LGH) as a battery charger is
certainly very feasible. It is fashionable to design these
chargers such that the battery is always connected to it.
Since the Buck topology is not isolated, shorting the input
terminals or capacitors of an unpowered
regulator/charger could allow damaging current flow
through the body diode of the high side MOSFET that
would be unprotected by a conventional input fuse. It is
recommended to connect the PI354x-00 family to the
battery using an active ORing device if LGH mode is used
as a constant current battery charger. The same should be
considered for super-capacitor applications as well.
Cool-Power®
Page 32 of 37
Rev 1.3
2/2016
vicorpower.com
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