Datasheet

UWE Series
Wide Input, Isolated
Eighth-Brick DC-DC Converters
MDC_UWE Series.E04 Page 21 of 23
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Dynamic control of the remote on/off function is facilitated with a mechanical
relay or an open-collector/open-drain drive circuit (optically isolated if appropri-
ate). The drive circuit should be able to sink appropriate current (see Performance
Specs) when activated and withstand appropriate voltage when deactivated.
Applying an external voltage to the On/Off Control when no input power is
applied to the converter can cause permanent damage to the converter.
Trimming Output Voltage
UWE converters have a trim capability that allows users to adjust the output
voltages. Adjustments to the output voltages can be accomplished via a trim pot
(Figure 6) or a single fi xed resistor as shown in Figures 7 and 8. A single fi xed
resistor can increase or decrease the output voltage depending on its connec-
tion. The resistor should be located close to the converter and have a TCR 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 to the +Output, or +Sense where
applicable, will increase the output voltage in this confi guration. A resistor con-
nected from the Trim to the –Output, or –Sense where applicable, will decrease
the output voltage in this confi guration.
Trim adjustments greater than the specifi ed range can have an adverse
affect on the converter's performance and are not recommended. Excessive
voltage differences between V
OUT and Sense, in conjunction with trim adjust-
ment of the output voltage, can cause the overvoltage protection 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 and sense functions can cause output voltages to increase,
thereby increasing output power beyond the converter'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
Note: Resistor values are in k. Adjustment accuracy is subject to resistor
tolerances and factory-adjusted output accuracy. V
O = desired output voltage.
Remote Sense Note: The Sense and V
OUT lines are internally connected
through low value resistors. Nevertheless, if the sense function is not used for
remote regulation the user should connect the +Sense to +V
OUT and –Sense
to –V
OUT at the DC-DC converter pins.
UWE series converters have a sense feature to provide point of use regula-
tion, thereby overcoming moderate IR drops in pcb conductors or cabling.
The remote sense lines carry very little current and therefore require minimal
cross-sectional-area conductors. The sense lines are used by the feedback
control-loop to regulate the output. As such, they are not low impedance points
and must be treated with care in layouts and cabling. Sense lines on a pcb
should be run adjacent to dc signals, preferably ground. In cables and discrete
wiring applications, twisted pair or other techniques should be implemented.
LOAD
R2
+VOUT
+VIN
–VIN
ON/OFF
CONTROL
TRIM
+SENSE
–VOUT
–SENSE
Figure 8. Trim Connections To Decrease Output Voltages
1M
5-20
TURNS
LOAD
+VOUT
+VIN
–VIN
ON/OFF
CONTROL
TRIM
+SENSE
–VOUT
–SENSE
Figure 6. Trim Connections Using A Trimpot
LOAD
R1
+VOUT
+VIN
–VIN
ON/OFF
CONTROL
TRIM
+SENSE
–VOUT
–SENSE
Figure 7. Trim Connections To Increase Output Voltages Using a Fixed Resistor