UNR-5/8-D12 Murata Power Solutions Inc, UNR-5/8-D12 Datasheet - Page 4

• Manufacturer Part Number: UNR-5/8-D12
• Description: DC/DC Converters & Regulators 40W 12V to 5V 8A
• Manufacturer: Murata Power Solutions Inc
• Series: UNRr

Specifications of UNR-5/8-D12

• Product: Non-Isolated / POL
• Output Power: 40 W
• Input Voltage Range: 10.8 V to 13.6
• Input Voltage (nominal): 12 V
• Number Of Outputs: 1
• Output Voltage (channel 1): 5 V
• Output Current (channel 1): 8 A
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

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Input Fusing
UNR 18-33W Series DC/DC converters are not internally fused. Certain
applications and or safety agencies may require the installation of fuses
at the inputs of power conversion components. For Murata Power Solu-
tions UNR Series DC/DC converters, you should use either slow-blow or
normal-blow fuses with values no greater than twice the expected input
current at full power. See Ordering Guide.
Input Overvoltage and Reverse-Polarity Protection
UNR 18-33W Series DC/DC converters do not incorporate either input over-
voltage or input reverse-polarity protection. Input voltages in excess of the
listed absolute maximum ratings and input polarity reversals of longer than
"instantaneous" duration can cause permanent damage to these devices.
On/Off Control
The On/Off Control pin may be used for remote on/off operation. UNR 18-
33W Series DC/DC converters are designed so that they are enabled when
the control pin is pulled high or left open (normal mode) and disabled when
the control pin is pulled low (to less than +0.8V relative to Logic Ground). As
shown in Figure 2, D5 models have internal 4.99k pull-up resistors to V
(+Input), while D12 models have 12.4k .
Dynamic control of the on/off function is best accomplished with a mechani-
cal relay or open-collector/open-drain drive circuit (optically isolated if appro-
priate). The drive circuit should be able to sink appropriate current when
activated and withstand appropriate voltage when deactivated.
Applying an external voltage to the On/Off Control pin when no input power is
applied to the converter can cause permanent damage to the converter. The
on/off control function, however, is designed such that the converter can be
disabled (control pin pulled low) while input voltage is ramping up and then
"released" once the input has stabilized. The time duration between the point
at which the converter is released and its fully loaded output settles to within
specified accuracy can be found in the Performance/Functional Specifica-
tions Table. See Start-Up Time for more details.
Start-Up Time
The V
ramping input voltage crosses the lower limit of the specified input voltage
range (4.75V for D5 models, 10.8V for D12 models) and the fully loaded
output voltage enters and remains within it specified accuracy band. Actual
measured times will vary with heavy capacitive loading.
The On/Off to V
Remote 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. See Typical Performance Curves
for details
Output Overvoltage Protection
UNR 18-33W Series DC/DC converters do not incorporate output overvolt-
age protection. In the extremely rare situation in which the device’s feedback
loop is broken, the output voltage may run to excessively high levels. If it is
absolutely imperative that you protect your load against any and all possible
overvoltage situations, voltage limiting circuitry must be provided external to
the power converter.
IN
to V
OUT
Start-Up Time is the interval between the time at which a
OUT
Start-Up Time assumes the converter is turned off via the
IN
Output Overcurrent Detection
Overloading the output of a power converter for an extended period of time
will invariably cause internal component temperatures to exceed their maxi-
mum ratings and eventually lead to component failure. High-current-carrying
components such as transformers, FET's and diodes are at the highest risk.
UNR 18-33W Series DC/DC converters incorporate an output overcur-
rent detection and shutdown function that serves to protect both the power
converter and its load.
When the output current of a thermally stabilized converter exceeds the
maximum rating by 40% (typical) to 80% (maximum), the internal overcurrent
detection circuit shuts down the converter by discharging the soft-start circuit
of the pulse width modulator (PWM). In this off state, which is similar to that
achieved by pulling the On/Off Control low, the output voltage quickly drops
as the output capacitors discharge into the load. Since there is no longer any
output current, the overcurrent detection circuit is released, allowing the soft-
start circuit to recharge and the converter to turn on again. If the faulty load
condition persists, the overcurrent detection circuit will again discharge the
soft-start circuit and shut down the converter. This continuous on/off cycling
of the converter is referred to as “hiccup mode.” Once the overload condition
is removed, the converter remains on, and the output voltage is quickly
restored to its regulated value.
The components used to sense the output current have large temperature
coefficients. Consequently, in a "cold-start" situation, the Overcurrent Detec-
tion Point may temporarily move to 80% to 120% above the rated current
specification. The device quickly heats up, particularly if an overload situation
exists, and restores the normal (40%) Overcurrent Detection Point. The
device will not be damaged by starting up into an output-short-circuit condition.
The overcurrent detection circuitry helps keep internal current levels and
operating temperatures within safe operating limits. Nevertheless, sustained
operation at current levels above the rated output current but below the Over-
current Detection Point may result in permanent damage to the converter.
Output Voltage Trimming
UNR 18-33W devices can be trimmed to any voltage between 1.50V and
3.55V. Trimming is accomplished with either a trimpot or a single fixed resis-
tor. The trimpot should be connected between +Output and Output Return
with its wiper connected to the Trim pin as shown in Figure 3 below.
Single Output, Non-Isolated, 5 or 12V
Technical enquiries email: [e-mail], tel:
Figure 2. Driving the On/Off Control Pin
UNR D5/D12 Series
+INPUT
D12 Models 12.4k
ON/OFF
CONTROL
LOGIC
GROUND
D5 Models 4.99k
8 and 10 Amp DC/DC Converters
R
PULL UP
UNR18-33W.B01 Page 4 of 10
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to 1.8/2.5/3.3V
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