UNR-1.8/2-D5SM データシートの表示（PDF） - DATEL Data Acquisition products

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UNR-1.8/2-D5SM

Surface-Mount, Non-Isolated 1.8/2.5/3.3V, 3.6-10W DC/DC Converters

DATEL Data Acquisition products  

UNR Series

NON-ISOLATED, 3.6-10W, SURFACE-MOUNT DC/DC CONVERTERS

TECHNICAL NOTES

I/O Filtering and Noise Reduction

All "D5" models of UNR SM Series 3.6-10W DC/DC converters achieve their

rated ripple and noise specifications without the use of external input/output

capacitors. The UNR-3.3/3-D12SM is tested and specified with a single,

external 22µF input capacitor (minimally rated for 1.5Arms ripple current and

120mΩ ESR).

In critical applications, input/output ripple/noise may be further reduced by

installing additional external I/O caps. Input capacitors, which function primarily

as energy-storage elements, should be selected for bulk capacitance, low ESR

and high rms-ripple-current ratings. Output capacitors, which function more as

true filter elements, should be selected for bulk capacitance, low ESR, and

appropriate frequency response. All caps should have appropriate voltage

ratings and be mounted as close to the converters as possible. Temperature

variations for all parameters should obviously be taken into consideration.

The most effective combination of external I/O capacitors will be a function of

your line voltage and source impedance, as well as your particular load and

layout conditions. Our Applications Engineers will be happy to recommend

potential solutions and can discuss the possibility of our modifying a given

device’s internal filtering to meet your specific requirements. Contact our

Applications Engineering Group for additional details.

Return Current Paths

The Input Return (pin 8), Output Return (pin 7) and Logic Ground (pin 2) are all

connected to each other internal to each device. To the extent possible, all load

current should be returned through pin 7 (via low-impedance runs) and all input

current returned through pin 8. Any control signals applied to pin 3 should be

referenced to pin 2. The internal trace leading to pin 2 is not designed to carry

high current. Devices should never be installed in a manner that results in high

current flow through pin 2 (i.e., pins 7 and 8 should never be left open or

attached via high-impedance connections).

Input Fusing

Certain applications and/or safety agencies may require the installation of fuses

at the inputs of power conversion components. Fuses should also be used if the

possibility of sustained, non-current-limited, input-voltage polarity reversals

exists. For DATEL UNR SM Series 3.6-10 Watt DC/DC Converters, you should

use slow-blow type fuses with values no greater than the following.

Model Number

UNR-1.8/2-D5SM

UNR-2.5/2-D5SM

UNR-3.3/3-D5SM

UNR-3.3/3-D12SM

Fuse Value

1.5 Amps

2 Amps

3 Amps

1.5 Amps

Start-Up Threshold and Undervoltage Shutdown (UNR-3.3/3-D12SM only)

Under normal start-up conditions, UNR-3.3/3-D12SM devices will not begin to

regulate until the ramping input voltage exceeds the Start-Up Threshold Voltage

(typically 10.2V). Once operating, devices will not turn off until the input voltage

drops below the Undervoltage Shutdown/Lockout limit (typically 9.6V).

Subsequent re-start will not occur until the input is brought back up to the Start-

Up Threshold. This built-in hysteresis obviously avoids any indeterminate on/off

conditions at a single voltage.

Start-Up Time

For the three "D5" models (that do not have an input turn-on threshold), the VIN

to VOUT Start-Up Time is the interval between the time a step input is applied to

the device and the fully loaded output voltage enters and remains within its

specified accuracy band.

For the UNR-3.3/3-D12SM, VIN to VOUT Start-Up Time is the interval between

the time at which a rapidly ramping input voltage crosses the turn-on threshold

point and the fully loaded output voltage enters and remains within its specified

accuracy band. Actual measured times will vary with input source impedance,

external input capacitance, and the slew rate and final value of the input voltage

as it appears to the converter.

The On/Off to VOUT Start-Up Time assumes the converter is turned off via the

On/Off Control with the nominal input voltage already applied to the converter.

The specification defines the interval between the time at which the converter is

turned on and the fully loaded output voltage enters and remains within its

specified accuracy band.

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