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VXR15-2800D Datasheet(PDF) 8 Page - VPT, Inc.
VPT [VPT, Inc.]
VXR15-2800D Datasheet(HTML) 8 Page - VPT, Inc.
/ 11 page
VXR15-2800D SERIES DATASHEET
SALES INFORMATION: phone (425) 353-3010 • fax (425) 353-4030 • firstname.lastname@example.org • www.vptpower.com
6.0 TECHNICAL NOTES
Please note that many of these functions are also demonstrated in detail on the VPT website in the
form of technical video labs.
6.1 GENERAL INFORMATION
6.1.1 Topology Description
The VXR15-2800D Series is an isolated dual-output DC-DC converter. Providing two separately controlled isolated outputs either of
which can be configured as positive or negative, the fixed frequency primary regulated flyback followed by a synchronous rectified
buck converter provides high efficiency over a wide input voltage range. The two stage topology provides tightly regulated output
voltages with fast transient response while eliminating analog feedback isolation. Implementing two independently controlled
outputs eliminates any cross regulation error caused by unbalanced load conditions.
6.1.2 External Components
The VXR15-2800D Series is designed to operate stand-alone and does not require external components for proper operation in
meeting the datasheet specifications. Input and output L-C filters are provided internally for low ripple and noise. To further reduce
output ripple and noise for more sensitive applications, a small ceramic capacitor, 1 µF to 10 µF, can be added to the output. Most
application specific ripple requirements can be met with the addition of output capacitors alone. External output capacitance can be
added up to the maximum listed in Section 3.2.
6.1.3 Source Impedance
The impedance of the 28 V input source can interact with the DC-DC converter and may affect performance. High source impedance
is often caused by a long input cable or components added in series with the input. Source resistance will cause a DC voltage drop as
the converter draws DC input current. This voltage drop is determined by multiplying the cable resistance by the input current at low
line. The voltage drop and the actual voltage at the input to the converter will determine the minimum source voltage at which the
converter will operate. A high source inductance can interact with the feedback control loop of the converter. VPT’s EMI filters will
typically isolate the source and eliminate this problem. In some cases, additional input capacitance may be needed to
stabilize the system.
6.1.4 Output Configurations
As each output of the converter is isolated both from the input and from each
other, either output can be configured as a positive or negative voltage. The
two outputs can also be stacked to create a single high voltage output. For
example the VXR15-281212D model can output +12V from Vout1 to OutCom1
and -12V from OutCom2 to Vout2. Connecting OutCom1 to Vout2 will provide
+24V from Vout1 to OutCom2.
6.2 FUNCTION DESCRIPTIONS
6.2.1 On/Off Control (Inhibit)
The INH (Inhibit) pin is a primary-side control pin referenced to INCOM. The
INH pin must be driven using an open collector or open drain configuration.
Pulling the INH pin low disables the converter output, removes bias voltage
from internal control circuitry and puts the converter in a state of minimum
input current draw. Leaving INH open enables the output, allowing the
converter to operate normally. The pin must be pulled below 1.5 V to disable
the output. An optional capacitor from INH to INCOM may be used to delay
turn-on. The INH pin should be left open if not used.
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