Datasheet

TECHNICAL NOTES
Input Voltage:
Continuous:
D12A Models 18 Volts
D24A Models 36 Volts
D48A Models 75 Volts
Transient (100msec):
D12A Models 25 Volts
D24A Models 50 Volts
D48A Models 100 Volts
On/Off Control (pin 4) Max. Voltages
Referenced to –Input (pin 2)
No Suffi x +V
IN
"N" Suffi x +VIN
Input Reverse-Polarity Protection Current must be <5 Amps. Brief
duration only. Fusing recommended.
Output Current Current limited. Devices can
withstand sustained output short
circuits without damage.
Case Temperature +100°C
Storage Temperature –40 to +120°C
Lead Temperature See soldering guidelines
These are stress ratings. Exposure of devices to greater than any of these conditions may
adversely affect long-term reliability. Proper operation under conditions other than those
listed in the Performance/Functional Specifi cations Table is not implied.
Absolute Maximum Ratings
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 Murata Power Solutions A-Series UWR 26-40 Watt DC/
DC Converters, you should use slow-blow type fuses with values no greater
than the following.
Model Fuse Value
UWR-3.3/8-D12 7 Amps
UWR-3.3/9-D24 4 Amps
UWR-3.3/9-D48 2 Amps
UWR-5/7-D12 8 Amps
UWR-5/8-D24 5 Amps
UWR-5/8-D48 3 Amps
Start-Up and Undervoltage Shutdown
Under normal start-up conditions, UWR 26-40W converters will not begin
to regulate properly until the ramping input voltage exceeds the Start-Up
Threshold. Once operating, devices will turn off when the applied voltage
droops below the Undervoltage Shutdown point. Devices will remain off as
long as the undervoltage condition continues. Units will automatically restart
when the applied voltage is brought back above the Start-Up Threshold.. The
hysteris is built into the function avoids an indeterminate on/off condition at
a single input voltage . See Performance/Functional Specifi cations table for
actual limits.
On/Off Control
The input-side, remote On/Off Control function (pin 4) can be ordered to
operate with either logic. Positive-logic devices (standard, no part-number
suffi x) are enabled when pin 4 is left open or is pulled high (+13V to V
IN
applied with respect to –Input, pin 2, (see Figure 2). Positive-logic devices
are disabled when pin 4 is pulled low (0-0.8V with respect to –Input).
Negative-logic devices are off when pin 4 open or pulled high (3.3V to +V
IN),
and on when pin 4 is pulled low (0-0.8V). See Figure 3.
Floating Outputs
Since these are isolated DC/DC converters, their outputs are "fl oating,"
with respect to the input. Designers will normally use the –Output (pin 7)
as the ground/return of the load circuit. You can, however, use the +Output
(pin 6) as ground/return to effectively reverse the output polarity.
Minimum Output Loading Requirements
UWR 26-40 Watt converters employ a synchronous-rectifi er design topology.
All models regulate within spec and are stable under no-load conditions.
Filtering and Noise Reduction
All UWR 26-40 Watt DC/DC Converters achieve their rated ripple and noise
specifi cations using the external output capacitor specifi ed in the Perfor-
mance/Functional Specifi cations table. In critical applications, input/output
noise may be further reduced by installing additional external I/O caps.
Input capacitors should be selected for bulk capacitance, low ESR and high
rms-ripple-current ratings. Input capacitors serve as energy-storage devices
to minimize variations in line voltage caused by transient IR drops in PCB
conductors from backplane to the DC/DC. Output capacitors should be
selected for low ESR and appropriate frequency response. All caps should
have appropriate voltage ratings and be mounted as close to the converters
as possible. The most effective combination of external I/O capacitors will be
a function of your particular load and layout conditions.
4
2
1
+VIN
13V CIRCUIT
5V CIRCUIT
–VIN
ON/OFF
CONTROL
Figure 2. Driving the Positive Logic On/Off Control Pin
www.murata-ps.com/support
UWR 26-40W Series
Single Output, High-Density, 3.3VOUT and 5 VOUT, 26-40 Watt, DC/DC Converters
MDC_UWR26-40W.D01 Page 4 of 10