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VXR15-2812SM Datasheet(PDF) 8 Page - VPT, Inc.
VPT [VPT, Inc.]
VXR15-2812SM Datasheet(HTML) 8 Page - VPT, Inc.
/ 12 page
VXR15-2800S 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 VXR15-2800S Series is an isolated single-output flyback DC-DC converter. The fixed frequency synchronous rectified flyback
topology provides high efficiency over a wide input voltage range. Proprietary secondary-side feedback control provides a tightly
regulated positive output voltage with fast transient response while eliminating analog feedback isolation.
6.1.2 External Components
The VXR15-2800S 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 curre nt 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
6.1.4 Output Configurations
Since the converter is isolated, the output can be configured as a positive or negative voltage. For example, the VXR15-2812S can
provide +12 V DC referenced to OUTCOM or -12 V DC referenced to +VOUT.
The outputs of multiple converters can be stacked in series to provide higher voltages. When outputs of multiple modules are
stacked, they naturally share the load. For example, two VXR15-2812S converters can be stacked to provide a 24 V DC output
at 30 W.
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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