7
Tyco Electronics Corp.
Advance Data Shee t
May 2001 18 Vdc to 36 Vdc or 36 Vdc to 75 Vdc Inputs
QW030xx DUAL Series Power Modules: dc-dc Converters;
Design Considerations (continued)
Input Source Impedance
The power module should be connected to a low
ac-impedance input source. Highly inductive source
impedances can affect the stability of the power mod-
ule. If the input source inductance exceeds 4 µH, a
33 µF electrolytic capacitor (ESR < 0.7 ¾ at 100 kHz)
mounted close to the power module helps ensure sta-
bility of the unit.
Safety Considerations
QW Modules
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 ex tra-low voltage
(SELV), all of the following must be true:
■The input source is to be provided with reinforced
insulation from any hazardous voltages, including 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
voltages do not appear at the module ’s output.
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 pin and ground.
The power module has e xtra-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
Two remote on/off options are available. Positive logic
remote on/off turns the module on during a logic-high
voltage on the remote ON/OFF pin, and off during a
logi c lo w. Ne gat iv e lo gic re mote on/o ff , de vi ce co de suf -
fix “1,” turns the module off during logic-high voltage
and on during a logic low.
To turn the power module on and off, the user must
supply a switch to control the voltage between the
on/off terminal and the VI(–) ter mi nal (Von/off). The
switch ma y be an open collector or equivalent (see
Figure 4). A logic low is Von/off = –0.7 V to 1.2 V. The
maximum 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 power module is 15 V. The maximum allowable
leakage current of the switch at Von/off = 15 V is 50 µA.