Datasheet

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Data subject to change. Copyright © 2005-2012 Avago Technologies. All rights reserved. Obsoletes 5988-7528EN
AV02-3679EN - June 25, 2012
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 icker-
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 modu-
lation 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 briey 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.
The temperature of the display will also aect the LED
brightness as shown in Figure 10.
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 D
5
= L, BIT D
4
= L) and the PWM is
set to 60% duty factor (BIT D
3
= H, BIT D
2
= H, BIT D
1
= L,
BIT D
0
= H). The resulting brightness is 44% (0.73 x 0.60 =
0.44) of full scale.
The temperature of the display will also aect the LED
brightness as shown in Figure 10.
Appendix F. Reference Material
Application Note 1027: Soldering LED Components
Application Note 1015: Contrast Enhancement Techniques
for LED Displays
Figure 10. Relative luminous Intensity versus ambient temperature.
YELLOW
HER/ORANGE
GREEN
AlGaAs
-55 856545255-15-35
0.2
3.0
2.6
2.2
1.8
1.4
1.0
0.6
T
A
– AMBIENT TEMPERATURE – °C
RELATIVE LUMINOUS INTENSITY
(NORMALIZED TO 1 AT 25° C)