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DOC-MN-007-03 VCCM600 User Manual
Vox Power Limited | Unit 2, Red Cow Interchange Estate, Ballymount, Dublin 22, D22 Y8H2, Ireland | T +353 1 4591161 | www.vox-power.com
Reverse Current Protection (RCP)
The standard output modules use synchronous rectification in the output stages to achieve high efficiency and as a result the outputs can both source and sink
current. The sink current is internally limited to approximately -6% of the maximum rated current. However, in applications where the output modules are
connected to external power sources such as batteries or other power supplies certain precautions must be observed to prevent damage to the unit.
The outputs should never be directly connected to to external power sources without some form of reverse current protection such as an external diode or
controlled mosfet. If protection is not used, large reverse currents which will ultimately result in damage to the unit will occur, especially when the AC mains is
disconnected.
Output Module Average and Peak Power
All modules have an average and peak power rating. The average power of each unit must at all times remain below it’s specified limit. However, each output can
deliver up to 150% of it’s average power rating for a maximum of 5 seconds at 50% duty cycle, subject to the current limit not being exceeded and subject to the
overall average power drawn being less than the specified average power rating (including any input derating due to temperature or line voltage). The available
peak power is a function of the output voltage and maximum current for each module. Full peak power is only possible when the output voltage is adjusted to
V
MAX
and the maximum current is drawn from the module. Note that both average and peak power ratings are subject to the same temperature derating as the
input module (derate by 2.5% per °C above 50°C), but are not subject to any line derating.
Start-up & Shut Down
All outputs are designed to have a regulated monotonic start-up with a rise time of
approximately 3ms as shown in the diagram right. The power good signal will not assert until
the voltage exceeds the power good threshold (≈90%).
Where multiple output modules are used, the default start up scheme is ratio-metric with all
outputs starting at the same time as shown in the diagram right. External control circuits may
be used to implement tracking or sequenced start up if necessary.
The outputs are not designed to start into pre-biased loads and may discharge any externally
capacitance before beginning to ramp the output voltage up in the normal way.
At shutdown, the outputs enter a high impedance state. Where no external load is present it
may take some time for the voltage to decay. When driving inductive loads, care must be taken
to limit the voltage at the output terminals to prevent damage to the unit.
Synchronisation
All output modules in the same product are synchronised. The typical operating frequency is
260kHz and paralleled or series connected units will not produce ripple beat frequencies.
External capacitance
All outputs can support a large external capacitance as detailed in the table shown.
The capacitances specified ensure monotonic start-up with rated load applied.
Larger capacitances can be applied for lower load currents.
OP
C
EXT_ MAX
A
12mF
B
4mF
C
1mF
D
500uF
