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参数资料
| 型号： | TWR-3.3/4-15/250-D12 |
| 元件分类： | 电源模块 |
| 英文描述： | 3-OUTPUT DC-DC REG PWR SUPPLY MODULE |
| 文件页数： | 5/9页 |
| 文件大小： | 301K |
| 代理商： | TWR-3.3/4-15/250-D12 |
TWR Models
2 2 W A T T , T R I P L E O U T P U T D C / D C C O N V E R T E R S
5
Safety Considerations
The TWR’s must be installed with consideration for any local safety,
certication or regulatory requirements. These vary widely but generally are
concerned with properly sized conductors, adequate clearance between
higher voltage circuits, life testing, thermal stress analysis of components
and ammability of components. Contact DATEL if you need further advice
on these topics.
Remote On/Off Control
The TWR models include an input pin which can turn on or shut off the
converter by remote signal. For positive logic models (no model number
sufx), if this pin is left open, the converter will always be enabled as long as
proper input power is present. On/Off signal currents are referred to the Input
Common pin on the converter. There is a short time delay of several mil-
liseconds (see the specications) for turn on, assuming there is no signicant
external output capacitance.
The On/Off Control may also be supplied with negative logic (LO = on, HI =
off) using the “N” model number sufx. Here again, leaving the pin open on
either model will enable the converter. Positive logic models must have this
control pin pulled down for shutoff. Negative logic models must pull up this
control pin for shutoff.
Dynamic control of this On/Off input is best done with either a mechanical
relay (ground the pin to turn it off), solid state relay (SSR), an open collector
or open drain transistor, CPU bit or a logic gate. The pull down current is
18mA max. Observe the voltage limits listed in the specications for proper
operation. Suggested circuits are shown below.
Figure 3. On/Off Control With An External CMOS Gate
Figure 4. On/Off Control With An External Transistor
Isolation Considerations
These converters use both transformer and optical coupling to isolate the
inputs from the outputs. Ideal “oating” isolation implies ZERO CURRENT
owing between the two Common return sections of the input and output up
to the working isolation voltage limit. Real-world isolation on this converter
includes both an AC current path (through some small coupling capaci-
tance) and some DC leakage current between the two ground systems. To
avoid difculties in your application, be sure that there are not wideband,
high amplitude AC difference voltages between the two ground systems. In
addition, ground difference voltages applied by your external circuits which
exceed the isolation voltage, even momentarily, may damage the converter’s
isolation barrier. This can either destroy the converter or instantly render it
non-isolated.
Current Limiting and Short Circuit Condition
As the output load increases above its maximum rated value, the converter
will enter current limiting mode. The output voltage will decrease and the
converter will essentially deliver constant power. This is commonly called
power limiting.
If the current continues to increase, the converter will enter short circuit
operation and the PWM controller will shut down. Following a time-out
period, the converter will automatically attempt to restart. If the short circuit
is detected again, the converter will shut down and the cycle will repeat. This
operation is called hiccup autorecovery. Please be aware that excessive
external output capacitance may interfere with the hiccup autorestart.
Output Filtering and Noise Reduction
All switching DC/DC converters produce wideband output noise which
radiates both through the wiring (conducted emission) and is broadcast into
the air (radiated emission). This output noise may be attenuated by adding
a small amount of capacitance in parallel with the output terminals. Please
refer to the maximum output capacitance in the Specications.
The amount of capacitance to add depends on the placement of the cap
(near the converter versus near the load), the distance from the converter
to the load (and resulting series inductance), the topology and locations of
load elements if there are multiple parallel loads and the nature of the loads.
For switching loads such as CPU’s and logic, this last item recommends
that small bypass capacitors be placed directly at the load. Very high clock
speeds suggest smaller caps unless the instantaneous current changes are
high. If the load is a precision high-gain linear section, additional ltering and
shielding may be needed.
Many applications will need no additional capacitance. However, if more
capacitance is indicated, observe these factors:
1. Understand the noise-reduction objective. Are you improving the switching
threshold of digital logic to reduce errors? (This may need only a small
amount of extra capacitance). Or do you need very low noise for a preci-
sion linear “front end”?
2. Use just enough capacitance to achieve your objective. Additional capaci-
tance trades off increasing instability (actually adding noise rather than
reducing it), poor settling response, possible ringing or outright oscillation
by the converter. Excessive capacitance may also disable the hiccup
autorestart. Do not exceed the maximum output capacitance specication.
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