A
20 Watt NT Single 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# 041007-1
20 Watt NT Single Series Block Diagram
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
5 Year Warranty
Water Washable Case Design
Description
These 20 Watt NT converters are ideal for battery operated
industrial, medical control and remote data collection systems.
They have achieved an exceptionally low input/output
capacitance (290 pF) that is half that of comparable models.
This low capacitance contributes to their exceptional input/
output isolation.
Complete overload protection with independent pulse-by-
pulse current limiting and an overtemperature shutdown
circuit ensure zero-failure rate operation. Each converter is
encased in a five-sided, shielded and sealed water washable
case.
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A
20 Watt NT Single 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# 041007-1
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.
(2)
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/35V Tantalum capacitor
located 1" away from the converter to simulate
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A
20 Watt NT Single 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# 041007-1
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BOTTOM VIEW
SIDE VIEW
Mechanical tolerances unless otherwise noted:
X.XX dimensions: 0.020 inches
X.XXX dimensions: 0.005 inches
Applications Information
General Information
The 20 Watt NT Single series is also 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
single will provide zero failure rate operation.
A fully five-sided shielded, sealed, water washable case is
standard along with specified operation over the full industrial
temperature range of -40 to +90C.
NOTES (cont.)
*
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your PCB's standard decoupling. Input reflected ripple is measured
into a 10H source impedance.
(3)
To determine the correct fuse size, see CALEX Application
Notes.
(4)
Short term stability is specified after a 30 minute warmup
at full load, constant line and recording the drift over a 24
hour period.
(5)
The transient response is specified as the time required to settle
from a 50 to 75 % step load change (rise time of step = 2 Sec)
to a 1% error band.
(6)
Dynamic response is the peak overshoot voltage during the
transient response time as defined in note 5 above.
(7)
The input ripple rejection is specified for DC to 120 Hz ripple with
a modulation amplitude of 1% of Vin.
(8)
The Case is tied to the -IN pin.
(9)
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.
(10) The case thermal impedance is specified as the case
temperature rise over ambient per package watt dissipated.
(11) Specifications subject to change without notice.
(12) 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.
A
20 Watt NT Single 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# 041007-1
R1 = 470 OHM, 1/4W, 5%
R2 = 1.0K, 1/4W, 5%
R3 = 2.4K, 1/4W, 5%
R4, R5 = 4.99K, 1/4W, 5%
C1 = 0.01F, 100V, CER
D1 = 1N4448
Q1 = 2N3906
IC1 = TL431CLP
L1 = 2H
C1, C3 = 0.01F, CERAMIC
C2 = 10F/35V, TANTALUM
D1, D2 - Overvoltage clamp is optional, see text
For applications that require remote sensing, the circuit
shown in Figure 3 may be used. This circuit can adjust for up
to 0.25 Volts drop in a 5 Volt output. This is equivalent to 0.06
ohms at 4 Amps.
Figure 3.
This remote sensing circuit can be used to automatically adjust for
voltage drops in your system's wiring.
Figure 4.
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 10 kohms nominal for 3.3 and 5 Volt
units and 20 kohms for 12 and 15 Volt outputs.
Non Standard Output Voltages
The trim may be used to adjust a +5 output unit up to 5.2 Volts
for ECL applications.
+12 Volt units will trim around a range of approximately
+9.6 to +12.6 Volts. +15 Volt units will trim around a range of
approximately +12 to +15.75 Volts.
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 1.
Standard connections for the 20 Watt NT Single: 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.
The ON/OFF and +5 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 converter's 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 0.1 to 0.001 F bypasses may be used around your
PCB as required without harm.
Extremely low ESR capacitors (< 0.5 ohms) should not be
used at the input as this will cause peaking of the input filter's
transfer function and actually degrade the filter's 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 P-P.
General Operation
Figure 1 shows the recommended connections for the 20 Watt
NT Single DC/DC converter. A fuse is recommended to
protect the input circuit and should not be omitted.
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 typically
below 10 mV P-P.
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 4 shows the proper connections
to use the trim pin. If output trimming is not desired the trim pin
may be safely left floating.
A
20 Watt NT Single 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# 041007-1
Grounding
The input and output sections are fully floating from each
other. They may be operated 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 converter's 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.
Case Grounding
The case serves not only as a heat sink but also as an EMI
shield. The 0.02 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 pin. This connection is
shown on the block diagram. The case is floating from the
input, coupled only by the 290 pF of isolation capacitance.
Remote ON/OFF Pin 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.
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 Single Series can operate up to 90C case temperature
without derating. Case temperature may be roughly calculated
from ambient by knowing that the NT Singles 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 heat sinking?
Efficiency is approximately 86%. This leads to an input power
of about 17.4 Watts. The case temperature rise would be 2.4
Watts x 9.5 = 22.8C. This number is subtracted from the
maximum case temperature of 90C to get 67C.
This is a rough approximation to the maximum ambient
temperature. Because of the difficulty of defining ambient
temperature and the possibility that the load's 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 circuit's
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 Single Series ON/OFF pin. The
input impedance is approximately 20 kohms. The maximum 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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