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LW025 Single-Output-Series Power Modules: 36 Vdc to 75 Vdc Inputs; 25 W

Tyco Electronics 

LW025 Single-Output-Series Power Modules:

36 Vdc to 75 Vdc Inputs; 25 W

Advance Data Sheet

March 1999

Design Considerations

Grounding Considerations

For modules without the isolated case ground pin

option, the case is internally connected to the VI(+) pin.

For modules with the isolated case ground pin, device

code suffix “7,” the VI(+) pin is not connected to the

case.

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 extra-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.

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. For the test configuration in Figure 10, 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. For other highly inductive source

impedances, consult the factory for further application

guidelines.

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 1950, CSA C22.2 No. 950-95, and VDE 0805

(EN60950, IEC950).

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; and

■ One VI pin and one VO pin are to be grounded or

both the input and output pins are to be kept floating;

and

■ The input pins of the module are not operator acces-

sible; and

■ Another SELV reliability test is conducted on the

whole system, as required by the safety 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.

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

logic low. Negative logic, device code suffix “1,” remote

on/off turns the module off during a logic high 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(–) terminal (Von/off). The

switch can be an open collector or equivalent (see Fig-

ure 13). A logic low is Von/off = –0.7 V to 1.2 V. The max-

imum 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 6 V. The maximum allowable leak-

age current of the switch at Von/off = 6 V is 50 µA.

The module has internal capacitance to reduce noise

at the ON/OFF pin. Additional capacitance is not gen-

erally needed and may degrade the start-up character-

istics of the module.

8

Tyco Electronics Corp.

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