UEI25 查看數據表（PDF） - Murata Manufacturing
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UEI25 Datasheet PDF : 23 Pages
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UEI25 Series
Single Output Isolated 25-Watt DC/DC Converters
CAUTION: To avoid unplanned power down cycles, do not exceed EITHER the
maximum output voltage OR the maximum output power when setting the trim.
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 overtemperature 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
<Connect trim resistor
between Trim and –Vout>
Trim Down
<Connect trim resistor
between Trim and +Vout>
UEI25-033-D48
12775
RTUP (Ω) = VO – 3.3 – 2050
5110 x (Vo –2.5)
RTDOWN (Ω) =
3.3 – VO
– 2050
UEI25-050-D48
CAUTION: While it is possible to control the On/Off with external logic if you
carefully observe the voltage levels, the preferred circuit is either an open
drain/open collector transistor or a relay (which can thereupon be controlled by
logic). The On/Off prefers to be set at approx. +15V (open pin) for the ON state,
assuming positive logic.
CAUTION: Do not apply voltages to the On/Off pin when there is no input
power voltage. Otherwise the converter may be permanently damaged.
On/Off Enable Control Ground Bounce Protection
To improve reliability, if you use a small signal transistor or other external
circuit to select the Remote On/Off control, make sure to return the LO side
directly to the –Vin power input on the DC/DC converter. To avoid ground
bounce errors, do not connect the On/Off return to a distant ground plane or
current-carrying bus. If necessary, run a separate small return wire directly to
the –Vin terminal. There is very little current (typically 1-5 mA) on the On/Off
control however, large current changes on a return ground plane or ground bus
can accidentally trigger the converter on or off. If possible, mount the On/Off
transistor or other control circuit adjacent to the converter.
−INPUT
+OUTPUT
RTUP (Ω) =
12775
VO – 5
– 2050
5110 x (Vo –2.5)
RTDOWN (Ω) =
5 – VO
– 2050
UEI25-120-D48
ON/OFF
CONTROL
TRIM
RTRIM DOWN
LOAD
25000
RTUP (Ω) = VO – 12 – 5110
10000 (Vo-2.5)
RTDOWN (Ω) =
12 – VO
– 5110
+INPUT
−OUTPUT
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 specified 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 +15VDC with respect to –VIN. An internal
bias current causes the open pin to rise to +VIN. Positive-polarity devices are
disabled when the On/Off is grounded or brought to within a low voltage (see
Specifications) with respect to –VIN.
Negative: Models with negative polarity are on (enabled) when the On/Off is
grounded or brought to within a low voltage (see Specifications) with respect to
–VIN. The device is off (disabled) when the On/Off is left open or is pulled high
to +15VDC Max. with respect to –VIN.
Dynamic control of the On/Off function should be able to sink the specified
signal current when brought low and withstand specified voltage when brought
high. Be aware too that there is a finite time in milliseconds (see Specifications)
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.
There are two CAUTIONs for the On/Off Control:
Figure 4. Trim adjustments to decrease Output Voltage using a Fixed Resistor
−INPUT
+OUTPUT
ON/OFF
CONTROL
TRIM
R TRIM UP
LOAD
+INPUT
−OUTPUT
Figure 5. Trim adjustments to increase Output Voltage using a Fixed Resistor
+VCC
ON/OFF
CONTROL
-INPUT
Figure 6. Driving the On/Off Control Pin (suggested circuit)
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MDC_UEI25W.B03 Page 21 of 23
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