SCE5740, SCE5741, SCE5742, SCE5743, SCE5744, SCE5745

2006-03-30

11

Electrical and Mechanical Considerations

Thermal Considerations

Optimum product performance can be had when the following

electrical and mechanical recommendations are adopted. The IC

is constructed in a high speed CMOS process, consequently noise

on the SERIAL DATA, SERIAL DATA CLOCK, LOAD and RESET

lines may cause incorrect data to be written into the serial shift reg-

ister. Adhere to transmission line termination procedures when

using fast line drivers and long cables (> 10 cm).

Good ground and power supply decoupling will insure that

I

ground bounce. Therefore it is recommended that each display

package use a 0.1 µmF and 0 µF capacitor between V

ground.

When the internal MUX Clock is being used connect the CLKSEL

pin to V

nected to the system’s reset control, it is recommended that this

pin be connected to the center node of a series 0.1 µF and 100 k

Ω

RC network. Thus upon initial power up the RESET will be held

low for 10 ms allowing adequate time for the system power supply

to stabilize.

ESD Protection

The input protection structure of the SCE574x provides significant

protection against ESD damage. It is capable of withstanding dis-

charges greater than 2.0 kV. Take all the standard precautions,

normal for CMOS components. These include properly grounding

personnel, tools, tables, and transport carriers that come in con-

tact with unshielded parts. If these conditions are not, or cannot be

met, keep the leads of the device shorted together or the parts in

anti-static packaging.

Soldering Considerations

The SCE574x can be hand soldered with SN63 solder using a

grounded iron set to 260°C.

Wave soldering is also possible following these conditions: Pre-

heat that does not exceed 93°C on the solder side of the PC board

or a package surface temperature of 85°C. Water soluble organic

acid flux (except carboxylic acid) or rosin-based RMA flux without

alcohol can be used.

Wave temperature of 245°C ± 5°C with a dwell between 1.5 sec. to

3.0 sec. Exposure to the wave should not exceed temperatures

above 260°C for five seconds at 1.59 mm (0.063") below the seating

plane. The packages should not be immersed in the wave.

Post Solder Cleaning Procedures

The least offensive cleaning solution is hot D.I. water (60°C) for

less than 15 minutes. Addition of mild saponifiers is acceptable. Do

not use commercial dishwasher detergents.

For faster cleaning, solvents may be used. Exercise care in choos-

ing solvents as some may chemically attack the nylon package.

For further information refer to Appnotes 18 and 19.

An alternative to soldering and cleaning the display modules is to

use sockets. Naturally, 14 pin DIP sockets 7.62 mm (0.300”) wide

with 2.54 mm (0.100") centers work well for single displays. Multi-

ple display assemblies are best handled by longer SIP sockets or

DIP sockets when available for uniform package alignment.

Optical Considerations

The 4.57 mm (0.180") high character of the SCE574x gives read-

ability up to five feet. Proper filter selection enhances readability

over this distance.

Using filters emphasizes the contrast ratio between a lit LED and

the character background. This will increase the discrimination of

different characters. The only limitation is cost. Take into consider-

ation the ambient lighting environment for the best cost/benefit

ratio for filters.

Incandescent (with almost no green) or fluorescent (with almost no

red) lights do not have the flat spectral response of sunlight. Plas-

tic band-pass filters are an inexpensive and effective way to

strengthen contrast ratios. The SCE5740 is a red display and

should be used with long wavelength pass filter having a sharp

cut-off in the 600 nm to 620 nm range. The SCE5742 is a

super-red display and should be used with long wavelength pass

filter having a sharp cut-off in the 570 nm to 600 nm range. The

SCE5744 is a high efficiency green display and should be used

with long wavelength pass filter that peaks at 565 nm.

Additional contrast enhancement is gained by shading the

displays. Plastic band-pass filters with built-in louvers offer the next

step up in contrast improvement. Plastic filters can be improved

further with anti-reflective coatings to reduce glare.

Optimal filter enhancements are gained by using circular polar-

ized, anti-reflective, band-pass filters. The circular polarizing fur-

ther enhances contrast by reducing the light that travels through

the filter and reflects back off the display to less than 1%.

Several filter manufacturers supply quality filter materials. Some of

them are: Panelgraphic Corporation, W. Caldwell, NJ; SGL Homa-

lite, Wilmington, DE; 3M Company, Visual Products Division, St.

Paul, MN; Polaroid Corporation, Polarizer Division, Cambridge,

MA; Marks Polarized Corporation, Deer Park, NY, Hoya Optics,

Inc., Fremont, CA.One last note on mounting filters: recessing dis-

plays and bezel assemblies is an inexpensive way to provide a

shading effect in overhead lighting situations. Several Bezel manu-

facturers are: R.M.F. Products, Batavia, IL; Nobex Components,

Griffith Plastic Corp., Burlingame, CA; Photo Chemical Products of

California, Santa Monica, CA; I.E.E.-Atlas, Van Nuys, CA. The

trade-off is fuzzy characters. Mounting the filters close to the dis-

play reduces this effect. Take care not to overheat the plastic filter

by allowing for proper air flow.

Microprocessor Interface

The microprocessor interface is through the serial port, SPI port or

one out of eight data bits on the eight bit parallel port and also con-

trol lines SDCLK and LOAD.

Power Up Sequence

Upon power up display will come on at random. Thus the display

should be reset at power-up. The reset will set the Address Regis-

ter to Digit 0, User RAM is set to 0 (display blank) the Control Word

is set to 0 (100% brightness) and the internal counters are reset.