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參數(shù)資料
| 型號： | 12D5.1700NT |
| 元件分類： | 電源模塊 |
| 英文描述： | 2-OUTPUT 20 W DC-DC REG PWR SUPPLY MODULE |
| 文件頁數(shù)： | 5/6頁 |
| 文件大?。?/td> | 146K |
| 代理商： | 12D5.1700NT |
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
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 90°C case temperature
without derating. Case temperature may be roughly calculated
from ambient by knowing that the NT Duals case temperature
rise is approximately 9.5°C 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 = 28.5°C. This number is subtracted from the
maximum case temperature of 90°C to get approximately:
62°C.
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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