unr-3.3-3000-d5 Murata Manufacturing Co., Ltd, unr-3.3-3000-d5 Datasheet - Page 5

• Manufacturer Part Number: unr-3.3-3000-d5
• Description: Single Output, Non-isolated, 3.3v 8-40 Watt, Dc/dc Converters
• Manufacturer: Murata Manufacturing Co., Ltd

Reducing Output Ripple/Noise
In addition to their internal output capacitors, UNR Series DC/DC convert-
ers require the installation of external output capacitors to achieve their
published ripple/noise specifications. The selected caps should be low-ESR,
tantalum or electrolytic types, and they should be located as close to the
converters as possible. Recommended values are listed in the table below.
Remote On/Off Control and the Logic Ground Pin
The On/Off Control pin (pin 2 on "D5" units) may be used for digitally con-
trolled on/off operation. A TTL logic high (+2 to +5 Volts, 250μA max.) ap-
plied to pin 2 disables the converter. A TTL logic low (0 to +0.8 Volts, 70μA
max.), or no connection, enables the converter. Control voltages should be
referenced to pin 1 (Logic Ground). Applying a voltage to the Control pin
when no input power is applied to the converter can cause permanent dam-
age to the converter.
The Input Return (pin 5), Output Return (pin 4) and Logic Ground (pin 1 on
"D5" models) are all tied together internal to the device. To the extent pos-
sible, load current should be returned to pin 4. Pin 5 should be connected
back to the input supply with as low an impedance as possible so that input
return current flows through pin 5. The internal trace leading to the Logic
Ground pin is not designed to carry high currents. Devices should not be
installed in a manner that results in high current flow through pin 2 (i.e., pins
4 and 5 should never be left open or attached via high-impedance connec-
tions).
"D12" models do not have On/Off Control functions. Their pin 2 (No Con-
nect) is not electrically connected to any internal circuitry and may be tied
to any convenient external run. Their pin 1 (Do Not Connect) is a test point.
Pin 1 may be soldered to an island for mechanical mounting purposes, but it
should not have an electrical connection to external circuitry.
Synchronization
Part Number
UNR-3.3/3000-D5
UNR-3.3/2500-D12
UNR-3.3/8000-D5
UNR-3.3/12000-D5
Output Capacitor
470μF, 6V, Low ESR
100μF, 6V, Low ESR
1000μF, 6V, Low ESR
1000μF, 6V, Low ESR
www.murata-ps.com
If desired, a synchronizing clock can be applied to pin 2 on "D5" models to
control the converter’s internal clock oscillator. The applied clock should be
a square wave with a maximum 1μsec "high" duration and an amplitude be-
tween +2V and +5V (see On/Off Control) referenced to pin 1 (Logic Ground).
The frequency of the synchronizing clock must be higher than that of the
standalone converter. Therefore, it should be 85kHz ±5kHz.
Synchronization Issues
Because of the comparatively small differential between their input and out-
put voltages, 5V-to-3.3V DC/DC converters capable of sourcing high output
current also demand high input current. Most of these high-current DC/DC’s
use switching architectures employing fixed-frequency clock oscillators, and
their input currents include both dc (average) and ac (ripple) components.
If you have multiple DC/DC’s connected to a single main power bus, you may
need to consider that all the converters will not be switching at exactly the
same frequency (due to normal component and manufacturing tolerances).
Consequently, the converters may randomly "self-synchronize" in their de-
manding of peak current from the main power bus. Peak currents all drawn
simultaneously can be significantly greater than the sum of average input
currents. This phenomenon can result in unwanted harmonic interactions
from converter to converter along the power bus.
One solution to this potential problem is to use the converters' On/Off Control
function to effectively "de-synchronize" their clocks. Forcing the multiple
clocks to be out of phase with each other relaxes the required performance
characteristics of the main power bus so the bus now has to carry the sum of
the average currents of all the converters plus only one peak current.
Technical enquiries email: [e-mail], tel:
Single Output, Non-Isolated, 3.3V
8-40 Watt, DC/DC Converters
MDC_UNR8-40W.B01 Page 5 of 6
UNR Series
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