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參數(shù)資料
| 型號(hào)： | 24S3.6XT |
| 英文描述： | SMPS Controller |
| 中文描述： | 開(kāi)關(guān)電源控制器 |
| 文件頁(yè)數(shù)： | 6/8頁(yè) |
| 文件大小： | 161K |
| 代理商： | 24S3.6XT |
45 Watt XT 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
6
3/2001
This will help to dampen the low frequency output ripple
without upsetting the dynamic operation of the XT. For more
information see our application note on
“
Understanding DC/
DC Converters Output Impedance
”
.
Another solution to the
“
No Load
”
condition is to use the
ON/OFF pin to control no load operation and shut the converter
down totally.
Dynamic response of the XT single will degrade when the
unit is operated with less than 25% of full rated power.
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 3.3 to 10 μF, 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. See
“
Applying the Output
”
for more information.
Another
“
Trick
”
that can be used when operating with a
common ground is to use a 10 to 100 μH 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 input or output circuits.
Be sure that the inductor has a self resonant frequency of
greater than 200 kHz and that the Q of the inductor is quite low.
If necessary to keep the inductor Q under control, parallel it
with a 200 to 1k ohm resistor.
Case Grounding
The copper case serves not only as a heat sink but also as a
EMI shield. The .025 inch thick case provides >30 dB of
absorption loss to both electric and magnetic fields at 220
kHz, while at the same time providing 20 to 40 % better heat
sinking over competitive thin steel, aluminum or plastic designs.
The case shield is tied to the -Input pin. This connection is
shown on the block diagram. The case is floating from the
output sections. The input is coupled to the outputs only by the
low 500 pF of isolation capacitance. This low I/O capacitance
insures that any AC common mode noise on the inputs is not
coupled to your output circuits.
Compare this isolation to the more usual 1000 - 2000 pF
found on competitive designs and you will see that CALEX
provides the very best DC and AC isolation available. After all,
you are buying an isolated DC/DC to cut ground loops. Don
’
t
let the isolation capacitance add them back in.
Temperature Derating
The XT Single series can operate up to 85
°
C case temperature
without derating. Case temperature may be roughly calculated
from ambient by knowing that the XT Singles case temperature
rise is approximately 4.4
°
C per package watt dissipated.
For example: If an XT converter is outputting 35 watts, at
what ambient could it expect to run with no moving air and no
extra heatsinking
Efficiency is approximately 80%, this leads to an input power
of 44 watts. The case temperature rise would be 9 watts
×
4.4
= 40
°
C. This number is subtracted from the maximum case
temperature of 85
°
C to get: 45
°
C.
This example calculation is for an XT single without any
extra heat sinking or appreciable air flow. Both of these factors
can greatly effect the maximum ambient temperature (see
below). Exact efficiency depends on input line and load
conditions, check the efficiency curves for exact information.
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,
these calculations should be verified by actual measurement
before committing to a production design.
Heat Sinking
The XT Single can be ordered in a
“
-I
”
configuration which
provides a case with 3 x M3 inserts located on the top surface
of the case for attaching a heat sink or mounting the converter
on it
’
s back using the inserts provided. The mounting surface
should be flat to within ±0.01 inches to prevent warping the XT
Single
’
s case.
The CALEX -HS heat sink was specially developed for this
model and can reduce the case temperature rise to typically
below 3.3
°
C per watt with natural convection and less with
moving air. It also increases the heat removing efficiency of
any cooling air flow.
When the XT single is ordered with a -I option and a -HS,
CALEX will ship the converter and heatsink attached. One
heat sink is needed for each converter ordered.
Customer installed heat sinks may also be used. It is
recommended that either liquid heatsink compound or nothing
be used on the heatsink interface. Stay away from the so
called
“
Dry
”
pad heat sink materials, in our experience these
materials are actually worse than no compound at all. Test
them thoroughly before committing to production.
Additional heatsinking will lower internal temperatures and
increase the expected operational life.
Mounting Kit
The MS9 chassis mounting kit allows for direct wire connection
to the XT single series pins. The mounting kit includes two
barrier strips for wire attachment. The MS9 may be conveniently
attached to a chassis by use of the 4 - 0.156 inch diameter
mounting holes provided at each corner.
Although the MS9 comes with solderless sockets, for
improved reliability in severe environmental or vibration
environments it is recommended that the XT Single be soldered
to the mounting kit.
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