TODX298

2001-07-26

8

7. Precaution on Use

(1)

Maximum rating

The maximum ratings are the limit values which must not be exceeded during operation of device.

None of these rating value must not be exceeded. If the maximum rating value is exceeded, the

characteristics of devices may never be restored properly. In extreme cases, the device may be

permanently damages.

(2)

Lifetime of light emitters

If an optical module is used for a long period of time, degeneration in the characteristics will mostly

be due to a lowering of the fiber output power (Pf). This is caused by the degradation of the optical

output of the LEDs used as the light source. The cause of degradation of the optical output of the

LEDs may be defects in wafer crystallization or mold resin stress. The detailed causes are, however,

not clear.

The lifetime of light emitters is greatly influenced by the operating conditions and the environment in

which it is used as well as by the lifetime characteristics unique to the device type. Thus, when a light

emitting device and its operating conditions determined, Toshiba recommend that lifetime

characteristics be checked.

Depending on the environment conditions, Toshiba recommend that maintenance such as regular

checks of the amount of optical output in accordance with the condition of operating environment.

(3)

Soldering

Optical modules are comprised of internal semiconductor devices. However, in principle, optical

modules are optical components. During soldering, ensure that flux does not contact with the emitting

surface or the detecting surface. Also ensure that proper flux removal is conducted after soldering.

Some optical modules come with a protective cap. The protective cap is used to avoid malfunction

when the optical module is not in use. Note that it is not dust or waterproof.

As mentioned before, optical modules are optical components. Thus, in principle, soldering where

there may be flux residue and flux removal after soldering is not recommended. Toshiba recommend

that soldering be performed without the optical module mounted on the board. Then, after the board

has been cleaned, the optical module should be soldered on to the board manually.

If the optical module cannot be soldered manually, use non−halogen (chlorine−free) flux and make

sure, without cleaning, there is no residue such as chlorine. This is one of the ways to eliminate the

effects of flux. In such a cases, be sure to check the devices’ reliability.

(4)

Noise resistance

It is believed that the use of optical transfer devices improve noise resistance. In theory, optical fiber

is not affected by noise at all. However, receiving modules which handle signals whose level is

extremely small, are susceptible to noise.

TOSLINK improve noise resistance to use a conductive case. However, the current signal output by

the optical receiving modules’ photodiode is extremely small. Thus, in some environments, shielding

the case may not achieve sufficient noise resistance.

First systems which incorporate TOSLINK, Toshiba recommend testing using the actual device to

check its noise resistance.

Use a simple noise filter on TOSLINK fiber optic transceiving module’s power line. If the ripple in the

power supply used is significant, reinforce the filter.

The optical module is to be used in an area which is susceptible to radiated noise, increase the

shielding by covering the optical module and the power line filter with a metallic cover.

(5)

Vibration and shock

This module is plastic sealed and has its wire fixed by resin. This structure is relatively resistant to

vibration and shock. In actual equipment, there are sometime cases in which vibration, shock, or

stress is applied to soldered parts or connected parts, resulting in lines cut. A care must be taken in

the design of equipment which will be subject to high levels of vibration.

(6)

Fixing fiber optical transceiving module

Solder the fixed pin (pins 9 and 10) of fiber optic transceiving module TODX298 to the printed circuit

board to fix the module to the board.

(7)

Shielding and wiring pattern of fiber optic transceiving modules

To shield, connect the fixed pins (pins 9 and 10) of fiber optic transceiving module TODX298 to the

GND.

Where the fiber optic transceiving module uses conductive resin, be careful that the case does not

touch wiring (including land).

To improve noise resistance, shield the optical module and the power line filter using a metallic cover.