HCMS-3901 Datasheet, PDF (18/18 Pages) AVAGO TECHNOLOGIES LIMITED – 3.3 V High Performance CMOS 5x7 AlphaNumeric Displays

Appendix C. Oscillator
The oscillator provides the internal refresh circuitry
with a signal that is used to synchronize the columns
and rows. This ensures that the right data is in the dot
drivers for that row. This signal can be supplied from
either an external source or the internal source.
A display refresh rate of 100 Hz or faster ensures
flicker-free operation. Thus, for an external oscillator the
frequency should be greater than or equal to 512 x 100 Hz
= 51.2 kHz. Operation above 1 MHz without the prescaler
or 8 MHz with the prescaler may cause noticeable pixel-
to-pixel mismatch.
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.
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 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.
The temperature of the display will also affect the LED
brightness as shown in Figure 10.
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
Appendix F. Reference Material
Application Note 1027: Soldering LED Components
Application Note 1015: Contrast Enhancement Techniques
for LED Displays
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Data subject to change. Copyright © 2005-2010 Avago Technologies. All rights reserved. Obsoletes AV01-0310EN
AV02-0868EN - August 20, 2010