AN-31
Description
Symbol Min
Typ
Max Units
Comment
Input
Input Voltage
VIN
36
29
48
75
36
VDC
VDC
VDC
VDC
VDC
Typical operational range
Input Voltage UV Turn ON
Input Voltage UV Turn Off
Input Voltage OV Turn On
Input Voltage OV Turn Off
72
90
Output
Output Voltage
Output Ripple and Noise
Output Current
VOUT
VRIPPLE
IOUT
4.8
0
5.00
50
5.2
V
mV
A
±4%
20 MHz Bandwidth
6.00
Line Regulation
Load Regulation
±0.2
±0.5
%
%
Transient Response Peak
Deviation
3
% of
VOUT
50-75% Load step, 100 mA/µs
48 VDC input
Transient Response Recovery
200
µs
To 1% of final output voltage,
50-75% load step, 48 VDC input
Total Output Power
Continuous Output Power
POUT
30
W
Efficiency
Low-Cost Design
Enhanced (non-sync rect.)
Synchronous Rectified Design
ηCost
84
87
91
%
%
%
Measured at POUT (30 W),
ηEnhanced
25 °C, 48 VDC Input
ηSyncRect
Environmental
Input-Output Isolation Voltage
Ambient Temperature
1500
-40
VDC
°C
TAMB
85
Free convection, sea level
Table 1. Typical Specifications for a Single Output DC-DC Converter.
Figure 1 shows a typical implementation of DPA-Switch in
a power supply with a single regulated output. This design
guide discusses considerations for selection of components
for a practical implementation of the circuit in Figure 1. It
also addresses options and tradeoffs in cost, efficiency and
complexitythatincludethesubstitutionofsynchronousrectifiers
and alternative generation of the bias voltage.
designer must guarantee that the converter becomes active and
fully functional at a voltage that is lower than the minimum.
Tolerance variations of the Line Undervoltage Threshold of
DPA-Switch with prudent design margin put the practical
minimum operating voltage closer to 30 V. Similarly, the
converter must be designed to operate at voltages higher than
the maximum specified input. The actual input voltage range
should be considered to be from about 30 V to 90 V for the
typical nominal input voltage of 48 VDC.
System Requirements
The design begins with an evaluation of the requirements.
Table 1 gives the specifications for the example converters
described here, that have been constructed and evaluated as
engineering prototypes. Variants of the basic design achieve
higher efficiencies with minor increases in complexity.
Output Characteristics
The output voltage can be maintained to ±4% over the range of
line, load and operational temperature range with an ordinary
feedbackcircuitthatusesaTL431regulator.Transientresponse
iscontrolledwithproperfrequencycompensation.Thedesignof
thefeedbacknetworkwithguidanceforselectionofcomponent
values is addressed in a separate section. Ripple and noise are
strongly influenced by the size of the output inductor and the
choice of output capacitors. These topics are discussed more
thoroughly later in this document.
Input Voltage Range
The actual input voltage range required for operation of the
converter is greater than that indicated by the specification. The
specification requires the converter to operate and to deliver
full performance at a minimum input of 36 V. Therefore, the
C
2
7/04
POWERINT [ Power Integrations ]
