Datasheet

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UEI15 Series
Isolated Wide Input Range 15-Watt DC/DC Converters
MDC_UEI15W.C14 Page 14 of 17
reduces the average output current, thereby preventing excessive internal
temperatures. A short circuit can be tolerated indefi nitely.
Trimming the Output Voltage
The Trim input to the converter allows the user to adjust the output voltage
over the rated trim range (please refer to the Specifi cations). In the trim equa-
tions and circuit diagrams that follow, trim adjustments use either a trimpot or
a single fi xed resistor connected between the Trim input and either the positive
or negative output terminals. (On some converters, an external user-supplied
precision DC voltage may also be used for trimming). Trimming resistors should
have a low temperature coeffi cient (±100 ppm/deg.C or less) and be mounted
close to the converter. Keep leads short. If the trim function is not used, leave
the trim unconnected. With no trim, the converter will exhibit its specifi ed
output voltage accuracy.
There are two CAUTIONs to be aware for the Trim input:
CAUTION: To avoid unplanned power down cycles, do not exceed EITHER the
maximum output voltage OR the maximum output power when setting the trim.
Be particularly careful with a trimpot. If the output voltage is excessive, the
OVP circuit may inadvertantly shut down the converter. If the maximum power
is exceeded, the converter may enter current limiting. If the power is exceeded
for an extended period, the converter may overheat and encounter overtem-
perature shut down.
Figure 4. Trim adjustments using a trimpot
LOAD
7
5-22
TURNS
+VOUT
TRIM
−VOUT
−VIN
ON/OFF
CONTROL
+VIN
Figure 6. Trim adjustments to increase Output Voltage using a Fixed Resistor
+VOUT
TRIM
ON/OFF
CONTROL
+VIN
LOAD
R TRIM UP
−VOUT
−VIN
Figure 5. Trim adjustments to decrease Output Voltage using a Fixed Resistor
LOAD
RTRIM DOWN
+VOUT
TRIM
ON/OFF
CONTROL
+VIN
−VOUT
−VIN
VO – 5
– 2050
12775
– 2050
5 – V
O
5110 (Vo - 2.5)
V
O – 12
– 5110
25000
– 5110
12 – V
O
10000 (Vo-2.5)
UEI15-050-Q12, Q48
UEI15-120-Q12, Q48
VO – 3.3
– 2050
12775
R
T
DOWN
() =RT
UP
() =
R
T
UP
() =
R
T
UP
() =
R
T
UP
() =
R
T
DOWN
() =
R
T
DOWN
() =
R
T
DOWN
() =
– 2050
3.3 – V
O
5110 (Vo - 2.5)
UEI15-033-Q12, Q48
VO – 15
– 5110
25000
– 5110
15 – V
O
10000 (Vo-2.5)
UEI15-150-Q12, Q48
Trim Up
<Connect trim
resistor between
Trim and −V
OUT>
Trim Down
<Connect trim
resistor between
Trim and +V
OUT>
CAUTION: Be careful of external electrical noise. The Trim input is a senstive
input to the converter’s feedback control loop. Excessive electrical noise may
cause instability or oscillation. Keep external connections short to the Trim
input. Use shielding if needed.
Trim Equations
Where Vo = Desired output voltage. Adjustment accuracy is subject to resis-
tor tolerances and factory-adjusted output accuracy. Mount trim resistor close
to converter. Use short leads.
Remote On/Off Control
On the input side, a remote On/Off Control can be ordered with either logic type.
Positive-logic models are enabled when the On/Off pin is left open or is
pulled high to +15V
max. with respect to –VIN. Some models will also turn on
at lower intermediate voltages (see Specifi cations). Positive-logic devices are