BWR33W Datasheet, PDF (6/12 Pages) Murata Power Solutions Inc. – Regulated 3.3V and 5V outputs

Input Reverse-Polarity Protection
Upon applying a reverse-polarity voltage to the DC/DC converter, an internal
diode will be forward biased, drawing excessive current from the power
source. Therefore, it is required that the input current be limited be either an
appropriately rated input fuse or a current limited power source.
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 a sustained, non-current-limited, input-voltage polarity
reversal exists. For DATEL BWR 33 Watt Series Converters, slow blow fuses are
recommended with values no greater than the following.
VIN Range
Fuse Value
"D12" Models
6 Amps
"D24" Models
4 Amps
"D48" Models
2 Amps
It is recommended that fuses be installed in the +Input line.
Trimming Output Voltages
These BWR converters have a trim capability (pin 8) that allow users to adjust
the output voltages ±5%. A trim adjustment will cause an equal percentage of
change in both outputs. Adjustments to the output voltages can be accom-
plished via a trim pot Figure 3 or a single fixed resistor as shown in Figures 4
and 5. A single fixed resistor can increase or decrease the output voltage
depending on its connection. Fixed resistors should be metal-film types with
absolute TCR’s less than 100ppm/°C to minimize sensitivity to changes in
temperature.
A single resistor connected from the Trim Pin (pin 8) the +3.3V Output (pin 7),
see Figure 4, will decrease the output voltages. A resistor connected from the
Trim Pin (pin 8) to Output Return (pin 6) will increase the output voltages.
Table 1 shows the typical Trim Resistor values for output voltage changes of
1 through 5%.
Trim adjustment greater than 5% can have an adverse affect on the
converter’s performance and is not recommended.
Trim Down
0%
1%
201.5k
2%
92.5k
3%
56.1k
4%
38.0k
5%
27.1k
Trim Up
123.7k
55.3k
32.6k
21.2k
14.3k
Table 1. Percentage of Output Voltage Change vs Trim Resistor Value (Ohms)
Dual Output BWR Models
Mixed Voltage, 5V AND 3.3V, 2” x 2”
33 Watt DC/DC Converters
1
+INPUT
2
–INPUT
5
+5V OUTPUT
OUTPUT ⁶
RETURN
4 _ON/OFF
CONTROL
7
+3.3V OUTPUT
TRIM
8
+5V LOAD
20kΩ
5-22 +3.3V LOAD
Turns
Figure 3. Trim Connections using a Trimpot
1
+INPUT
2
–INPUT
4 _ON/OFF
CONTROL
5
+5V OUTPUT
OUTPUT ⁶
RETURN
7
+3.3V OUTPUT
TRIM
8
R TRIM
DOWN
+5V LOAD
+3.3V LOAD
Figure 4. Decrease Output Voltage Trim Connections Using A Fixed Resistor
Trim Down
( ) ^{3.55(VO – 1.273)}
RT_DOWN (k7) =
–13
3.3 – VO
1
+INPUT
2
–INPUT
5
+5V OUTPUT
OUTPUT ⁶
RETURN
4 _ON/OFF
CONTROL
7
+3.3V OUTPUT
TRIM
8
+5V LOAD
+3.3V LOAD
R TRIM
UP
Figure 5. Increase Output Voltage Trim Connections Using A Fixed Resistor
Trim Up
( ) ^4.51
RT_UP (k7) = _{VO – 3.3} – 13
Note: Accuracy of adjustment is subject to the tolerances of
resistor values, reference accuracy and factory-adjusted output
accuracy. VO = desired output voltage.
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MDC_BWR 33W Models.A05 Page 6 of 12