TWR-3.3 データシートの表示（PDF） - Murata Power Solutions

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TWR-3.3

Isolated, High Reliability 1" x 2" DC/DC Converters

Murata Power Solutions 

Safety Considerations

The TWR’s must be installed with consideration for any local safety,

certification 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 flammability 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

suffix), 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

milliseconds (see the specifications) for turn on, assuming there is no

significant external output capacitance.

The On/Off Control may also be supplied with negative logic (LO = on, HI

= off) using the “N” model number suffix. 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 mechani-

cal 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 specifications

for proper operation. Suggested circuits are shown below.

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/./&&

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Figure 3. On/Off Control With An External CMOS Gate

K7490

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).054

/./&&

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3)'.!,

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#/.42/,,%2

#/--/.

Figure 4. On/Off Control With An External Transistor

www.murata-ps.com

Triple Output/TWR Models

Isolated, High Reliability 1" x 2" DC/DC Converters

Isolation Considerations

These converters use both transformer and optical coupling to isolate

the inputs from the outputs. Ideal “floating” isolation implies ZERO CUR-

RENT flowing 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

capacitance) and some DC leakage current between the two ground

systems. To avoid difficulties 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 Specifications.

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 recom-

mends 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, addi-

tional filtering 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 switch-

ing 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

precision linear “front end”?

2. Use just enough capacitance to achieve your objective. Additional

capacitance 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

specification.

Technical enquiries email: sales@murata-ps.com, tel: +1 508 339 3000

MDC_TWR22.B02 Page 5 of 9

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