A
20 Watt NT Dual Series DC/DC Converters
2401 Stanwell Drive Concord, California 94520 Ph: 925/687-4411 or 800/542-3355 Fax: 925/687-3333 www.calex.com Email: sales@calex.com
1
eco# 010403-2, eco# 041007-1
Features
Fully Self Contained, No External Parts
Required for Operation
Low and Specified Input/Output Capacitance
Efficiencies to 85%
Overcurrent Protected and Thermal Shutdown
Circuitry for Long, Reliable Operation
Five Sided Shielded Low Thermal Gradient
Copper Case
Five Year Warranty
Water Washable Case Design
Description
Designed to save valuable PC board space, the 20 Watt NT
Dual series is ideal for use in battery operated industrial,
medical control and remote data collection systems. Each unit
is completely filtered to reduce noise, has an exceptionally
low input/output capacitance and provides efficiencies to
85%.
Complete overload protection with independent pulse-by-
pulse current limiting and an overtemperature shutdown
circuit ensure zero-failure rate operation. Their copper cases
are five-sided, shielded and water washable.
20 Watt NT Dual Series Block Diagram
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UL Recognition only applies up to 60 VDC
A
20 Watt NT Dual Series DC/DC Converters
2401 Stanwell Drive Concord, California 94520 Ph: 925/687-4411 or 800/542-3355 Fax: 925/687-3333 www.calex.com Email: sales@calex.com
2
eco# 010403-2, eco# 041007-1
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*
UL Recognition only applies up to 60 VDC
A
20 Watt NT Dual Series DC/DC Converters
2401 Stanwell Drive Concord, California 94520 Ph: 925/687-4411 or 800/542-3355 Fax: 925/687-3333 www.calex.com Email: sales@calex.com
3
eco# 010403-2, eco# 041007-1
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BOTTOM VIEW
SIDE VIEW
Applications Information
The 20 Watt NT Dual series like all CALEX converters carries
the full 5 year CALEX no hassle warranty. We can offer a five
year warranty where others can't because with CALEX it's
rarely needed.
General Information
The 20 Watt NT Dual series is mindful of battery operation for
industrial, medical control and remote data collection
applications. The remote ON/OFF pin places the converter in
a very low power mode that draws typically less than 3 mA
from the input source.
Full overload protection is provided by independent pulse-
by-pulse current limiting and an over-temperature shutdown
circuit. These protection features assure you that our 20 Watt
Dual will provide you with zero failure rate operation.
A fully five sided shielding, sealed, water washable case is
standard along with specified operation over the full commercial
temperature range of -40 to +90C.
Mechanical tolerances unless otherwise noted:
X.XX dimensions: 0.020 inches
X.XXX dimensions: 0.005 inches
NOTES
*
All parameters measured at Tc=25C, nominal input
voltage and full rated load unless otherwise noted.
Refer to the CALEX Application Notes for the definition
of terms, measurement circuits and other information.
(1)
Noise is measured per CALEX Application Notes. Measurement
bandwidth is 0-20 MHz for peak-peak measurements, 10 kHz
to 1 MHz for RMS measurements. Output noise is measured
with a 0.01F ceramic in parallel with a 1F tantalum located
1" away from the converter to simulate your boards standard
decoupling. Input reflected ripple is measured into a 1 H
source impedance.
(2)
To determine the correct fuse size, see CALEX Application
Notes.
(3)
The Case is tied to the -Input pin.
(5)
Short term stability is specified after a 30 minute warmup at full
load, constant line and recording the drift over a 24 hour period.
(6)
The transient response is specified as the time required to settle
from a 50 to 75 % step load change on one output (rise time of
step = 2 Sec) to a 1% error band.
(7)
Dynamic response is the peak overshoot during a transient as
defined in note 6 above.
(8)
The input ripple rejection is specified for DC to 120 Hz ripple with
a modulation amplitude of 1% of Vin.
(10) The functional temperature range is intended to give an additional
data point for use in evaluating this power supply. At the
low functional temperature the power supply will function with no
side effects, however sustained operation at the high
functional temperature will reduce expected operational life.
The data sheet specifications are not guaranteed over the
functional temperature range.
(11) The case thermal impedance is specified as the case temperature
rise over ambient per package watt dissipated.
(12) Load regulation is defined as the voltage change on either output
as the loads on both outputs are changed from 25% to 100% full
load at the same time.
(13) Cross regulation is defined as the change in one output when the
other output is changed from 25% to 100% full load.
(14) Specifications subject to change without notice.
(15) Water Washability - Calex DC/DC converters are designed to
withstand most solder/wash processes. Careful attention should
be used when assessing the applicability in your specific
manufacturing process. Converters are not hermetically sealed.
*
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Note: On nominal 48Vin models UL recognition only applies up to 60 VDC
A
20 Watt NT Dual Series DC/DC Converters
2401 Stanwell Drive Concord, California 94520 Ph: 925/687-4411 or 800/542-3355 Fax: 925/687-3333 www.calex.com Email: sales@calex.com
4
eco# 010403-2, eco# 041007-1
D - Overvoltage clamp is optional, see text
*
*
*
- No connection needed if not used.
Figure 1.
Standard connections for the 20 Watt NT Dual. The ON/OFF and
TRIM pins can be left floating if they are not used. The input fuse
should not be omitted. The overvoltage diodes may be added to the
circuit directly at the converter to provide transient protection to your
circuit.
General Operation
Applying The Input
Figure 1 shows the recommended connections for the 20
Watt NT Dual DC/DC converter. A fuse is recommended to
protect the input circuit and should not be omitted. The fuse
serves the purpose of preventing unlimited current from
flowing in the case of a catastrophic system failure.
The ON/OFF and TRIM pins may be left floating if they are
not used. No external capacitance on either the input or
outputs is required for normal operation, in fact it can degrade
the converters performance. See our application note
"Understanding DC/DC Converters Output Impedance" and
the low noise circuits later in this data sheet for more
information. The usual 1 F to 10 F tantalum and 0.1 to
0.001 F ceramic bypasses may be used around your PCB
as required for local bypassing without harm.
Extremely low ESR capacitors (< 0.5 ohms) should not be
used at the input as this will cause peaking of the input filters
transfer function and actually degrade the filters performance.
Applying The Output
The output is simply connected to your application circuit and
away you go. If extra low output noise is required in your
application the circuit shown in Figure 2 may be used to
reduce the output noise to below 10 mV peak-peak.
The trim pin may be used to adjust the outputs by up to +5
% from the nominal factory setting to account for system
wiring voltage drops. Figure 3 shows the proper connections
to use the trim pin. If output trimming is not desired the trim pin
may be safely left floating.
Non Standard Output Voltages/Single
Ended Mode
The trim may be used to adjust a +5 output unit up to 5.2 volts
for ECL applications or to make up for line voltage drops. +5
output units will trim around a range of approximately +4.2 to
+5.3 volts.
+12 volt units will trim around a range of approximately
+7.4 to +12.9 volts and +15 volt units will trim around a range
of approximately +8.6 to +16 volts.
The dual outputs may also be used single-ended to get
10, 24 or 30 volts output at the full rated current of 1.7, 0.85
or 0.7 Amps (see figure 4). To use the single ended mode just
connect your load to the + and - output terminals and leave
the CMN output floating. Trimming of the output voltage may
also be done while using the outputs in the single ended
mode.
Maximum power from the module is limited to the specified
non-trimmed maximum (Typical Output Voltage x Maximum
Rated Load = Maximum Power). Trimming the output up
reduces the output current proportionally to keep the maximum
power constant. Output current is not increased over the
Rated Maximum when trimming the output voltage down.
See our application note on remote sense and trim
functions for more information.
Figure 2.
For very low noise applications the circuits shown above can be
used. The input current ripple will be reduced approximately 30 dB
of the original value while the output noise will be reduced to below
10 mV P-P.
Figure 3.
The output can be trimmed by either a trimpot or fixed resistors. If
fixed resistors are used their values may range from 0 to infinite
ohms. The trimpot should be 20 K ohms nominal.
A
20 Watt NT Dual Series DC/DC Converters
2401 Stanwell Drive Concord, California 94520 Ph: 925/687-4411 or 800/542-3355 Fax: 925/687-3333 www.calex.com Email: sales@calex.com
5
eco# 010403-2, eco# 041007-1
Operation
The remote ON/OFF pin may be left floating if this function is
not used. The equivalent input circuit for the ON/OFF pin is
shown in figure 5. The best way to drive this pin is with an open
collector/drain or relay contact. See our application note titled
"Understanding the remote ON/OFF function" for more
information about using the remote ON/OFF pin.
Figure 4.
To get 10, 24 or 30 volt outputs use the NT dual in the "Single Ended"
mode. In this mode the load is taken across the + to - pins with the
CMN pin left floating. Output Current in this mode is the full rated 1.7,
0.85 or 0.7 Amps. Output trimming may optionally be used as shown
in figure 3.
Grounding
The input and output sections are fully floating from each
other. They may be operated fully floating or with a common
ground. If the input and output sections are connected either
directly at the converter or at some remote location from the
converter it is suggested that a 1 to 10F, 0.5 to 5 ohm ESR
capacitor bypass be used directly at the converter output pins.
This capacitor prevents any common mode switching currents
from showing up at the converters output as normal mode
output noise. Do not use the lowest ESR, biggest value
capacitor that you can find! This can only lead to reduced
system performance or oscillation. See our application note
"Understanding Output Impedance For Optimum Decoupling"
for more information.
Another useful "Trick" that can be used when operating
with a common ground is to use a 10 to 100 H choke between
the grounds. This gives you a solid low frequency ground
connection, but looks like a high impedance to the switching
current effects and prevents them from flowing in the
connection. This will have the effect of preventing the common
mode currents from showing up as normal mode components
in your output or input circuits. Be sure that the "Q" of this
inductor is quite low and that the self resonant frequency is
above 220 kHz. If necessary to keep the inductor "Q" low,
parallel it with a 200 ohm to 1k ohm resistor.
Case Grounding
The case serves not only as a heat sink but also as a EMI
shield. The 0.016 inch thick copper provides >25 dB of
absorption loss to both electromagnetic and electric fields at
220 kHz, while at the same time providing about 30% better
heat sinking than competitive 0.01 inch thick steel cases.
The case shield is tied to the -Input. This connection is
shown on the block diagram. The case is floating from the
output, coupled only by the 500 pF of isolation capacitance.
When the ON/OFF pin is pulled low with respect to the -
Input, the converter is placed in a low power drain state. When
the ON/OFF pin is released the converter fully powers up in
typically 10 milliseconds. The ON/OFF pin turns the converter
off while keeping the input bulk capacitor fully charged, this
prevents the large inrush current spike that occurs when the
+input pin is opened and closed.
Temperature Derating
The NT Dual series can operate up to 90C case temperature
without derating. Case temperature may be roughly calculated
from ambient by knowing that the NT Duals case temperature
rise is approximately 9.5C per package watt dissipated.
For example: If a 24 volt input converter was delivering 15
Watts, at 24 volts input at what ambient could it expect to run
with no moving air and no extra heatsinking?
Efficiency is approximately 82%, this leads to an input
power of about 18 Watts. The case temperature rise would be
3 Watts x 9.5 = 28.5C. This number is subtracted from the
maximum case temperature of 90C to get approximately:
62C.
This is a rough approximation to the maximum ambient
temperature. Because of the difficulty of defining ambient
temperature and the possibility that the loads dissipation may
actually increase the local ambient temperature significantly
or that convection cooling is suppressed by physical placement
of the module. These calculations should be verified by actual
measurement of operating temperature and your circuits
exact efficiency (efficiency depends on both line input and
load value) before committing to a production design.
Figure 5.
The simplified schematic of the NT Dual series ON/OFF pin. The
input impedance is approximately 20 kohms. The open circuit
voltage is approximately 2.5 volts. By leaving this pin floating the
converter will be in the ON state. When the pin is pulled below 0.7
volts the converter is placed in the power down or OFF state. See
our application note on the remote ON/OFF function for more
information.
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