Datasheet

Trimming Output Voltage
UWR 26-40W converters have a trim capability (pin 8) that allows users
to adjust the output voltages ±5%. Adjustments to the output voltages
can be accomplished via a trim pot (Figure 5) or a single fi xed resistor as
shown in Figures 6 and 7. A single fi xed resistor can increase or decrease
the output voltage depending on its connection. Resistors should be located
close to the converter and have TCR's less than 100ppm/°C to minimize
sensitivity to changes in temperature. If the trim function is not used, leave
the trim pin fl oating.
A single resistor connected from the Trim (pin 8) to the +Output (pin 6),
will decrease the output voltage. A resistor connected from the Trim (pin 8)
to the –Output (pin 7) , –Sense where applicable, will increase the output
voltage.
Trim adjustments greater than the specifi ed ±5% can have an adverse
affect on the converter’s performance and are not recommended. Excessive
trim adjustment of the output voltage can cause the overvoltage protec-
tion circuitry to activate (see Performance Specifi cations for overvoltage
limits). Power derating is based on maximum output current and voltage
at the converter's output pins. Use of trim can cause output voltages to
increase thereby increasing output power beyond the UWR's specifi ed
rating or cause output voltages to climb into the output overvoltage region.
Therefore:
(V
OUT at pins) x (IOUT) <= rated output power
LOAD
+VOUT
–VIN
+VIN
ON/OFF
CONTROL
TRIM
–VOUT
7
2
1
8
6
4
20kΩ
5-22
TURNS
LOAD
R
TRIM DOWN
+VOUT
–VIN
+VIN
ON/OFF
CONTROL
TRIM
–VOUT
7
2
1
8
6
4
LOAD
R
TRIM UP
+VOUT
–VIN
+VIN
ON/OFF
CONTROL
TRIM
+SENSE
–VOUT
–SENSE
7
2
1
8
6
4
Figure 5. Trim Connections Using A Trimpot
Figure 6. Trim Connections To Decrease Output Voltages Using Fixed Resistors
Figure 7. Trim Connections To Increase Output Voltages Using Fixed Resistors
Note: Resistor values are in kΩ. Accuracy of adjustment is subject to the
tolerances of resistors and factory-adjusted output accuracy.
V
O = desired output voltage.
Trim Equations For 3.3 Volt Models
UP
VO – 3.3
R
T (kΩ) =
–13
3.06
DOWN
3.3 – VO
RT (kΩ) =
–13
2.49(VO – 1.23)
UP
VO – 5
R
T (kΩ) =
–16.9
6.25
DOWN
5 – VO
RT (kΩ) =
–16.9
2.49(VO – 2.51)
Trim Equations For 5 Volt Models
Soldering Guidelines
Murata Power Solutions recommends the specifi cations below when installing these
converters. These specifi cations vary depending on the solder type. Exceeding these
specifi cations may cause damage to the product. Be cautious when there is high
atmospheric humidity. We strongly recommend a mild pre-bake (100° C. for 30
minutes). Your production environment may differ; therefore please thoroughly review
these guidelines with your process engineers.
Wave Solder Operations for through-hole mounted products (THMT)
For Sn/Ag/Cu based solders:
Maximum Preheat Temperature 115° C.
Maximum Pot Temperature 270° C.
Maximum Solder Dwell Time 7 seconds
For Sn/Pb based solders:
Maximum Preheat Temperature 105° C.
Maximum Pot Temperature 250° C.
Maximum Solder Dwell Time 6 seconds
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UWR 26-40W Series
Single Output, High-Density, 3.3VOUT and 5 VOUT, 26-40 Watt, DC/DC Converters
MDC_UWR26-40W.D01 Page 6 of 10