Datasheet

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UEI30 Series
30W Isolated Wide-Range DC-DC Converters
MDC_UEI Series 30W.B02 Page 15 of 18
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 overtempera-
ture shut down.
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
Trim Up Trim Down
<Connect trim resistor
between Trim and –Vout>
<Connect trim resistor
between Trim and +Vout>
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 specifi ed with either positive
or negative logic as follows:
Positive: Models equipped with Positive Logic are enabled when the On/Off
pin is left open or is pulled high to +V
IN with respect to –VIN. An internal bias
current causes the open pin to rise to +V
IN. Some models will also turn on at
lower intermediate voltages (see Specifi cations). Positive-logic devices are
disabled when the On/Off is grounded or brought to within a low voltage (see
Specifi cations) with respect to –V
IN.
Negative: Models with negative logic are on (enabled) when the On/Off is
grounded or brought to within a low voltage (see Specifi cations) with respect to
–V
IN. The device is off (disabled) when the On/Off is left open or is pulled high
to +15V
DC Max. with respect to –VIN.
Dynamic control of the On/Off function should be able to sink the speci-
fi ed signal current when brought low and withstand appropriate voltage
when brought high. Be aware too that there is a fi nite time in milliseconds
(see Specifi cations) between the time of On/Off Control activation and stable,
regulated output. This time will vary slightly with output load type and current
and input conditions.
Figure 4. Trim adjustments using a trimpot
LOAD
7
5-22
TURNS
+VOUT
TRIM
−VOUT
−VIN
ON/OFF
CONTROL
+VIN
Figure 5. Trim adjustments to decrease Output Voltage using a Fixed Resistor
LOAD
RTRIM DOWN
+VOUT
TRIM
ON/OFF
CONTROL
−VIN
−VOUT
+VIN
UP
VO – 5
R
T (Ω) =
– 2050
12775
5 – V
O
RT (Ω) =
– 2050
5110 (Vo - 2.5)
DOWN
UP
VO – 12
R
T (Ω) =
– 5110
25000
12 – V
O
RT (Ω) =
–5110
10000 (Vo-2.5)
DOWN
UP
DOWN
UEI30-050-Q12/-Q48
UEI30-120-Q12/-Q48
UP
VO – 3.3
R
T (Ω) =
– 2050
12775
3.3 – V
O
RT (Ω) =
– 2050
5110 (Vo - 2.5)
DOWN
UEI30-033-Q12/-Q48
VO – 15
R
T (Ω) =
– 5110
25000
15 – V
O
RT (Ω) =
–5110
10000 (Vo-2.5)
UEI30-150-Q12/-Q48
Figure 6. Trim adjustments to increase Output Voltage using a Fixed Resistor
+VOUT
TRIM
ON/OFF
CONTROL
−VIN
LOAD
R TRIM UP
−VOUT
+VIN