HCMS-2819 Datasheet, PDF(12/12 Page) AVAGO TECHNOLOGIES LIMITED – High Performance CMOS 5x7 AlphaNumeric InGaN Blue Display

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HCMS-2819 Datasheet, PDF (12/12 Pages) AVAGO TECHNOLOGIES LIMITED – High Performance CMOS 5x7 AlphaNumeric InGaN Blue Display

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Appendix C. Oscillator

Appendix E. Display Brightness

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. 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.

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 8. The temperature of

the display will also affect the LED brightness as shown

in Figure 7.

Appendix F. Reference Material

Application Note 1027: Soldering LED Components

Application Note 1015: Contrast Enhancement Tech-

niques for LED Displays

Figure 7. Relative luminous intensity versus ambient temperature.

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AV02-2558EN - June 29, 2010