QTS48T25120 DC-DC Series Data Sheet
300-Watt Quarter-Brick Bus Converter
Features
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RoHS lead-free and lead-solder-exempt
products are available
Cost-effective, single board design
Ultra-high efficiency 96.2% @ full load
Low profile – 0.400” (10.16 mm)
Narrow Input Range 42 – 53 VDC
Paralleling option
Input-to-output isolation: 2000 VDC
Start-up into high capacitive load
Low conducted and radiated EMI
Output overcurrent protection
Input undervoltage lockout
Input overvoltage shutdown
Overtemperature protection
Approved to UL 60950/ CAN/CSA-C22.2 No.
60950-00, and TUV approved to EN 60950-1,
IEC 60950-1
Applications
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Intermediate Bus Architectures
Telecommunications equipment
LAN/WAN
Data processing
Description
The QTS48T25120 bus converter provides an isolated step-down voltage from 48V to 12.0V nominal. The QTS is
an unregulated converter; therefore output voltage is directly proportional to input voltage with a conversion ratio of
4:1. The converter provides ultra-high efficiency; as a result very little heat is dissipated and a heat sink is not
required.
The QTS48T25120 is an excellent choice for intermediate bus application where multiple output voltages are
required and a 12.0V rail will be used to power point-of-load devices.
Model Selection
Model
Input
Voltage
VDC
42-53
38-53
Input
Current,
Max ADC
7.5
7.5
Output
Voltage
Vout,@ 48Vin
VDC
12.0
12.0
Output
Current
ADC
25
25
Output
Ripple/Noise,
Typical
Efficiency @
48Vi, 25A
96.2
96.2
mV p-p (typ.)
75
75
QTS48T25120-NDA0
QTS48T25120-NCAS2
This product is intended for integration into end-use equipment. All the required procedures for CE marking of end-use equipment should be
followed.
MAY 31, 2005 revised to JUN 15, 2006
Page 1 of 8
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QTS48T25120 DC-DC Series Data Sheet
300-Watt Quarter-Brick Bus Converter
Absolute Maximum Ratings
Stresses in excess of the absolute maximum ratings may cause performance degradation, adversely effect long-
term reliability, and cause permanent damage to the converter.
Parameter
Input Voltage
Operating Temperature
Storage Temperature
Conditions/Description
Min
0
-40
-40
Max
53
120
125
Units
VDC
°C
°C
Continuous
PC Board Temperature
Environmental and Mechanical Specifications
All specifications apply over specified input voltage, output load, and temperature range, unless otherwise noted.
Parameter
Shock
Sinusoidal Vibration
Weight
Water Washing
MTBF
Conditions/Description
(Half-sinewave, 6ms), 3 axes
GR-63-CORE, Section 5.4.2
Standard process
Per Bellcore TR-NWT-000332 @
35°C
Min
Nom
50
1
1.2/35
Yes
2,100
Max
Units
g
g
Oz/g
kHrs
Isolation Specifications
All specifications apply over specified input voltage, output load, and temperature range, unless otherwise noted.
Parameter
Insulation Safety Rating
Isolation Voltage
Isolation Resistance
Isolation Capacitance
Conditions/Description
Input to Output
Min
2000
10
1100
Nom
Functional
Max
Units
VDC
MOhm
pF
Input Specifications
All specifications apply over specified input voltage, output load, and temperature range, unless otherwise noted.
Parameter
Input Voltage
Turn-On Input Voltage
Conditions/Description
QTS48T25120-NDAX - Continuous
QTS48T25120-NDAS2 - Continuous
QTS48T25120-NDAX - Ramping Up
QTS48T25120-NDAS2 – Ramping
Up
QTS48T25120-NDAX - Ramping
Down
QTS48T25120-NDAS2 – Ramping
Down
Within 1% of Vo nominal
Full Load, 12μH source inductance
Vin=Vin.max
Vin
Page 2 of 8
55
52
57
54
Min
42
38
38
36
36
34
3
Nom
48
48
40.5
36.5
37.5
34.5
Max
53
53
41.3
37.3
40.5
35.3
20
50
1
58
55
www.power-one.com
ms
mA p-p
A
2
s
Units
VDC
VDC
Turn-Off Input Voltage
VDC
Turn On Time
Input Reflected Ripple Current
Inrush Transient
Input Over-voltage Shutdown
Turn-off voltage threshold
Turn-on voltage threshold
MAY 31, 2005 revised to JUN 15, 2006
QTS48T25120 DC-DC Series Data Sheet
300-Watt Quarter-Brick Bus Converter
Output Specifications
All specifications apply over specified input voltage, output load, and temperature range, unless otherwise noted.
Parameter
Output Voltage over line load and
temperature
Output Current
Load Regulation
Turn-on overshoot
Transient response
Admissible Load Capacitance
Output Current Limit Threshold
Auto Re-start (Latch if parallel option
is selected)
Switching Frequency
Over input voltage range
Vo
Vo
25% load step change @ 1A/uS
(% of Vo nominal)
I
rated
, Nom Vin
A
110%
125%
Vo
Conditions/Description
Min
9.7
0
Nom
Max
13.5
25
500
3
+/-3
3000
150%
Units
VDC
A
mV
%
%
μF
360
kHz
Feature Specifications
All specifications apply over specified input voltage, output load, and temperature range, unless otherwise noted.
Parameter
Shutdown (ON/OFF)
Negative Logic
Converter ON
Source Current
Converter OFF
Positive Logic
Converter ON
Open Circuit Voltage
Converter OFF
Overtemperature Protection
Conditions/Description
On/Off signal is low – converter is ON
-0.5
ON/OFF pin is connected to -Vin
2.5
On/Off signal is low–converter is OFF
2.5
ON/OFF pin is floating
-0.5
Average board temperature
+120
Vin
5
0.8
+130
VDC
VDC
VDC
°C
0.8
1
Vin
VDC
mADC
VDC
Min
Nom
Max
Units
MAY 31, 2005 revised to JUN 15, 2006
Page 3 of 8
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QTS48T25120 DC-DC Series Data Sheet
300-Watt Quarter-Brick Bus Converter
The QTS48T25120 converter does not require any
external components for proper operation. However,
if the distribution of the input voltage to the converter
contains significant inductance, the capacitor C1
may be required to enhance performance of the
converter.
A minimum of a 100μF electrolytic
capacitor (with ESR<0.5Ω @ 100kHz) mounted
close to the input side of the power module will
ensure stability of the unit.
Refer to the “Inrush Current Control Application
Note” on www.power-one.com for suggestions on
how to limit the magnitude of the inrush current.
For output decoupling we recommend to use a 10μF
low ESR tantalum (AVX TPSC106M025R0500 is
used in our test setup) and a 1μF ceramic
capacitors.
Note, that the capacitors do not
substitute the filtering required by the load.
Shutdown Feature Description
The ON/OFF pin in the QTS48T25120 converter
functions as a normal soft shutdown. It is referenced
to the –Vin pin (see Figure 2). With the positive
logic, when the ON/OFF pin is pulled low, the output
is turned off and the unit goes into a very low input
power mode.
With negative logic, when the ON/OFF pin is pulled
low, the unit is turned on.
An open collector switch is recommended to control
the voltage between the ON/OFF pin and the -Vin
pin of the converter. The ON/OFF pin is pulled up
internally, so no external voltage source is required.
The user should avoid connecting a resistor between
the ON/OFF pin and the +Vin pin.
When the ON/OFF pin is used to achieve remote
control, the user must take care to insure that the pin
reference for the control is really the -Vin pin. The
control signal must not be referenced ahead of EMI
filtering, or remotely from the unit. Optically coupling
the information and locating the optical coupler
directly at the module will solve any of these
problems.
Note:
If the ON/OFF pin is not used, it can be left floating (positive logic),
or connected to the -Vin pin (negative logic).
Characteristic Curves
98
96
94
Efficiency in %
92
90
88
86
84
Efficiency vs Load Current
42V Input
48V Input
53V Input
10% 20% 30% 40% 50% 60% 70% 80% 90% 100%
Percentage of Full Load
Figure 1. QTS48T25120 Efficiency vs. Output Load
Typical Application
Figure 2 shows the recommended connections for
the QTS48T25120 converter.
Figure 2. Typical Application of QTS48T25120
MAY 31, 2005 revised to JUN 15, 2006
Page 4 of 8
www.power-one.com
QTS48T25120 DC-DC Series Data Sheet
300-Watt Quarter-Brick Bus Converter
based standards, one of the following requirements
must be met in the system design:
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If the voltage source feeding the module is SELV
or TNV, the output of the converter may be
grounded or ungrounded.
If the voltage source feeding the module is ELV,
the output of the converter may be considered
SELV only if the output is grounded per the
requirements of the standard.
This information is provided for guidance only
and the user is responsible for any design
considerations regarding safety.
Safety Considerations
The QTS48T25120 converter features 2000 Volt DC
isolation from input to output. The input-to-output
resistance is greater than 10MΩ. This converter is
provided with functional insulation between input and
output circuits according to all IEC60950 based
standards. Nevertheless, if the system using the
converter needs to receive safety agency approval,
certain rules must be followed in the design of the
system. In particular, all of the creepage and
clearance requirements of the end-use safety
requirements must be observed. These documents
include UL60950 - CSA60950-00 and EN60950,
although other or additional requirements may be
needed for specific applications.
The QTS48T25120 converter has no internal fuse.
The external fuse must be provided to protect the
system from catastrophic failure as shown in Figure
2. The fuse with a rating not greater than 10A is
recommended. The user can select a lower rating
fuse based upon the highest inrush transient at the
maximum input voltage and the maximum input
current of the converter, which occurs at the
minimum input voltage. Both input traces and the
chassis ground trace (if applicable) must be capable
of conducting a current of 1.5 times the value of the
fuse without opening. The fuse must not be placed
in the grounded input line, if any.
In order for the output of the QTS48T25120
converter to be considered as SELV (Safety Extra
Low Voltage) or TNV-1, according to all IEC60950
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Thermal Considerations
The QTS48T25120 converter is designed for natural
or forced convection cooling.
The maximum
allowable output current of the converter is
determined by meeting the derating criteria for all
components used in the converter. For example, the
maximum semiconductor junction temperature is not
allowed to exceed 125°C to ensure reliable long-term
operation of the converter. Contact Power-One for
the complete list of the derating criteria.
The graph in figure 3 shows the maximum output
current of the QTS48T25120 converter at different
ambient temperatures under both natural and forced
(transverse airflow direction, from pin 1 to pin 3)
convection.
For example, the QTS48T25120 operating at 48Vin,
70°C can deliver up to 21A reliably with 200LFM
forced air.
MAY 31, 2005 revised to JUN 15, 2006
Page 5 of 8
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