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LW020G

Single-Output-Series Power Modules: 36 Vdc to 75 Vdc Inputs; 20 W

Tyco Electronics -> TE Connectivity 

Data Sheet

January 2000

LW020 Single-Output-Series Power Modules:

36 Vdc to 75 Vdc Inputs; 20 W

Feature Descriptions (continued)

Synchronization (Optional)

power of the module should not exceed the rated

power for the module as listed in the Ordering Informa-

tion table.

The unit is capable of external synchronization from an

independent time base with a switching rate of

256 kHz. The amplitude of the synchronizing pulse

train is TTL compatible and the duty cycle ranges

between 40% and 60%. Synchronization is referenced

to VI(+).

Thermal Considerations

Introduction

The LW020 Single-Output-Series power module oper-

ates in a variety of thermal environments; however, suf-

ficient cooling should be provided to help ensure

reliable operation of the unit. Heat-dissipating compo-

nents inside the unit are thermally coupled to the case.

Heat is removed by conduction, convection, and radia-

tion to the surrounding environment. Proper cooling

can be verified by measuring the case temperature.

Peak case temperature (TC) occurs at the position indi-

cated in Figure 15.

26.9

(1.06)

TRIM

ON/OFF

NC

–

–

OUT

IN LW020A81

+ DC-DC CONVERTER +

IN:DC 36-75V, 1.1A

OUT:DC 5.0V, 4A

MADE IN USA

19.6

(0.77)

CASE PIN (OPTIONAL)

8-1265(C)

Note: Dimensions are in millimeters and (inches). Pin locations are

for reference only.

Figure 15. Case Temperature Measurement

Location

Note that the view in Figure 15 is of the metal surface

of the module—the pin locations shown are for refer-

ence. The temperature at this location should not

exceed the maximum case temperature indicated in

the derating curve shown in Figure 16. The output

Heat Transfer

Increasing airflow over the module enhances the heat

transfer via convection. Figure 16 shows the maximum

power that can be dissipated by the module without

exceeding the maximum case temperature versus local

ambient temperature (TA) for natural convection

through 3.0 ms–1 (600 ft./min.).

Systems in which these power modules may be used

typically generate natural convection airflow rates of

0.3 ms–1 (60 ft./min.) due to other heat-dissipating com-

ponents in the system. Therefore, the natural convec-

tion condition represents airflow rates of up to 0.3 ms–1

(60 ft./min.). Use of Figure 16 is shown in the following

example.

Example

What is the minimum airflow necessary for a LW020A

operating at VI = 48 V, an output current of 3.6 A, and a

maximum ambient temperature of 85 °C?

Solution:

Given: VI = 48 V, IO = 3.6 A, TA = 85 °C

Determine PD (Figure 18): PD = 4.5 W

Determine airflow (Figure 16): v = 1.0 ms–1

(200 ft./min.)

7

MAX CASE

TEMPERATURE

6

5

4

NATURAL

3

CONVECTION

1.0 ms-1 (200 ft./min.)

2.0 ms-1 (400 ft./min.)

2

3.0 ms-1 (600 ft./min.)

1

0

40 50 60 70 80 90 100 110 120

MAX AMBIENT TEMPERATURE, TA (˚C)

8-1264(C).a

Note: Conversion factor for linear feet per minute to meters per

second: 200 ft./min. = 1 ms–1.

Figure 16. Forced Convection Power Derating;

Either Orientation

Tyco Electonics Corp.

11

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