HCMS-39X2 Datasheet, PDF (21/22 Pages) Agilent(Hewlett-Packard) – 3.3 V High Performance CMOS 5x7 AlphaNumeric Displays

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.
Appendix E. Display
Brightness
Appendix F. Reference
Material
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
Register 0 holds the word
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.
Application Note 1027:
Soldering LED Components
Application Note 1015: Contrast
Enhancement Techniques for
LED Displays
The temperature of the display
will also affect the LED bright-
ness as shown in Figure 10.
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
-50
ORANGE
RED
0
50
100
AMBIENT TEMPERATURE – °C
Figure 10. Relative luminous Intensity versus ambient temperature.
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