VXR15-2800D SERIES DATASHEET

3.0

SALES INFORMATION: phone (425) 353-3010 • fax (425) 353-4030 • vptsales@vptpower.com • www.vptpower.com

8

+

12V

-

+

24V

-

+

12V

-

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.