PI354X-00 Datasheet, PDF (33/39 Pages) –

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. The total external loading on VDR must be less than I_VDR.
2. No direct connection is allowed. Any noise source that can
disturb the VDR voltage can also affect the internal controller
operation. A series inpedance is required between the VDR pin
and any external circuitry.
3. All loads must be locally de-coupled using a 0.1µF ceramic
capacitor. This capacitor must be connected to the VDR output
through a series resistor no smaller than 1kΩ, which forms a
low-pass filter.
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 60V 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^® ZVS Switching Regulators
Page 33 of 39
Rev 1.6
03/2017
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