8Tyco Electronics Corp.
Data Sheet
November 2001
36 Vdc to 75 Vdc In; 3. 3 Vdc and 5 Vdc Out; 16.5 W and 25 W
LUW025-Series Power Modules: dc-dc Converters:
Safety Considerations
For safety-agency approval of the system in which the
power module is used, the power module must be
installed in compliance with the spacing and separation
requirements of the end-use safety agency standard,
i.e., UL 60950, CSA C22.2 No. 60950-00, and VDE
0805 (IEC60950).
If the input source is non-SELV (ELV or a hazardous
voltage greater than 60 Vdc and less than or equal to
75 Vdc), for the module's output to be considered
meeting the requirements of safety extra-low voltage
(SELV), all of the following must be true:
■The input source is to be provided with reinforced
insulation from any other hazardous voltages, includ-
ing the ac mains.
■One VI pin and one VO pin are to be grounded or
both the input and output pins are to be kept floating.
■The input pins of the module are not operator acces-
sible.
■Another SELV reliability test is conducted on the
whole system, as required by the saf ety agencies, on
the combination of supply source and the subject
module to verify that under a single fault, hazardous
vol tag es do not appear at the module 's outpu t.
Note: Do not ground either of the input pins of the
module without grounding one of the output
pins. This may allow a non-SELV voltage to
appear between the output pins and ground.
The power module has e xtr a-low voltage (ELV) outputs
when all inputs are ELV.
The input to these units is to be provided with a maxi-
mum 5 A normal-blow fuse in the ungrounded lead.
Feature Descriptions
Overcurrent Protection
To provide protection in a fault (output overload) condi-
tion, the unit is equipped with internal current-limiting
circuitry and can endure current limiting for an unlim-
ited duration. At the point of current-limit inception, the
unit shifts from voltage control to current control. If the
output voltage is pulled very low during a severe fault,
the current-limit circuit can exhibit either foldback or
tailout characteristics (output-current decrease or
increase). The unit operates normally once the output
current is brought back into its specified range.
Remote On/Off
The remote on/off signal is referenced to the primary
and is available with either positive or negative logic.
Positive logic remote on/off turns the module on during
a logic-high voltage on the REMOTE ON/OFF pin, and
off during a logic low. Negative logic, device code suffix
“1,” turns the module off during a logic high and on dur-
ing a logic low and is the factory-pref erred configuration
(see the Feature Specifications tab le).
To turn the power module output on and off, the user
must supply a switch to control the voltage between the
on/off terminal and the VI(–) termi nal (Von/off). The
switch may be an open collector or equivalent (see Fig-
ure 13). A logic low is Von/off = 0 V to 1.2 V. The maxi-
mum Ion/off during a logic low is 1 mA. The switch
should maintain a logic-low voltage while sinking 1 mA.
During a logic high, the maximum Von/off generated by
the pow er module is 10 V. The maximum allowable
leakage current of the switch at Von/off = 10 V is 50 µA.
8-758e
Figure 13. Remote On/Off Implemen tat ion
Output Voltage Set-Point Adjustment
(Trim)
Output voltage adjustment (trim) allows the user to
increase or decrease the output voltage set point of a
module. This is accomplished by connecting an exter-
nal resistor between the TRIM pin and either the VO(+)
or VO(–) p in.
Connecting an external resistor between the TRIM pin
and VO(–) pin (Radj-down) decreases the output voltage
set point (see Figure 14). In order to maintain the out-
put voltage accuracy, the trim resistor tolerance should
be ±0.1%.
+
Ion/off
-
Von/off
REMOTE
ON/OFF
VI(+)
VI(-)
LOAD
VO(-)
VO(+)