HCMS-39X2 datasheet(21/22 Pages) HP

21 / 22 page

Appendix D. Refresh Circuitry

This display driver consists of 20

one-of-eight column decoders and

20 constant current sources, 1

one-of-eight row decoder and

eight row sinks, a pulse width

modulation control block, a peak

current control block, and the

circuit to refresh the LEDs. The

refresh counters and oscillator

are used to synchronize the

columns and rows.

The 160 bits are organized as 20

columns by 8 rows. The IC

illuminates the display by

sequentially turning ON each of

the 8 row-drivers. To refresh the

display once takes 512 oscillator

cycles. Because there are eight

row drivers, each row driver is

selected for 64 (512/8) oscillator

cycles. Four cycles are used to

briefly blank the display before

the following row is switched on.

Thus, each row is ON for 60

oscillator cycles out of a possible

64. This corresponds to the

maximum LED on time.

Figure 10. Relative luminous Intensity versus ambient temperature.

-50

AMBIENT TEMPERATURE – °C

2.0

1.6

1.4

1.0

0.6

0.2

100

ORANGE

RED

0.4

0.8

1.2

1.8

Appendix F. Reference

Material

Application Note 1027:

Soldering LED Components

Application Note 1015: Contrast

Enhancement Techniques for

LED Displays

Appendix E. Display

Brightness

Two ways have been shown to

control the brightness of this

LED display: setting the peak

current and setting the duty

factor. Both values are set in

Control Word 0. To compute the

resulting display brightness when

both PWM and peak current

control are used, simply multiply

the two relative brightness

factors. For example, if Control

1001101, the peak current is

73% of full scale (BIT D5=L, BIT

D4 = L) and the PWM is set to

60% duty factor (BIT D3 = H,

BIT D2 = H, BIT D1 = L, BIT D0

= H). The resulting brightness is

44% (.73 x .60 = .44) of full

scale.

The temperature of the display

will also affect the LED bright-

ness as shown in Figure 10.

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