SCE5780
Row Strobing
Row
Load
0
1
2
3
4
5
6
0 1 2 3 4
Columns
Load Row 0
0
1
2
3
4
5
6
0 1 2 3 4
Columns
Load Row 1
0
1
2
3
4
5
6
0 1 2 3 4
Columns
Load Row 2
0
1
2
3
4
5
6
0 1 2 3 4
Columns
Load Row 3
0
1
2
3
4
5
6
0 1 2 3 4
Columns
Load Row 4
0
1
2
3
4
5
6
0 1 2 3 4
Columns
Load Row 5
0
1
2
3
4
5
6
0 1 2 3 4
Columns
IDXX5192
Load Row 6
The SCE578X allows a high frequency external oscillator source
to drive the display. Data bit, D4, in the control word format con-
trols the prescaler function. The prescaler allows the oscillator
source to be divided by 16 by setting D4=1. However, the pres-
caler should not be used, i.e., when using the internal oscillator
source.
The Software Clear (C0
HEX
), given in Table „Software Clear“,
clears the Address Register and the RAM. The display is blanked
and the Character Address Register will be set to Character 0. The
internal counter and the Control Word Register are unaffected.
The Software Clear will remain active until the next data input cycle
is initiated.
Software Clear
Op code
D7 D6
1
1
Control Word
D5 D4 D3 D2
0
0
0
0
Hex
D1
0
D0
0
C0
CLEAR
Operation
To determine the power deration with a given ambient tempera-
ture, use the following formula:
T
jmax
=
T
A
+
P
D
⋅ θ
ja
T
jmax
=maximum IC junction temperature
P
D
=power dissipated by the ICs
θ
ja
=thermal resistance, junction to ambient
To determine the power dissipation of the display, use the following
formula:
where:
PD
=
N
⋅
I
LL
⁄
140
⋅
RB
N=number of LEDs on
I
LL
/140=average current for a single LED
RB=relative brightness level
A typical thermal resistance value (θ
ja
) for this display is 50 °C/W
when mounted in a socket soldered on a 1.57 mm (0.062") thick
PCB with 0.5 mm (0.020"), 1 ounce copper traces and the display
covered by a plastic filter. The display’s maximum IC junction tem-
perature is 125°C. Power Deration Curve is based on these typical
values.
where:
Multiplexer and Display Driver
The eight characters are row multiplexed with RAM resident col-
umn data. The strobe rate is established by the internal or external
MUX Clock rate. The MUX Clock frequency is divided by a 320
counter chain. This results in a typical strobe rate of 768 Hz. By
pulling the Clock SEL line low, the display can be operated from an
external MUX Clock. The external clock is attached to the CLK I/O
connection.
An asynchronous hardware Reset (pin 24) is also provided. Bring-
ing this pin low will clear the Character Address Register, Control
Word Register, RAM, and blanks the display. This action leaves the
display set at Character Address 0, and the Brightness Level set at
100%, prescaler ÷1.
Electrical and Mechanical Considerations
Thermal Considerations
The display’s power usage may need to be reduced to operate at
high ambient temperatures. The power may be reduced by lower-
ing the brightness level, reducing the total number of LEDs illumi-
nated, or lowering
V
LED
. The
V
CC
supply, relative to the
V
LED
supply, has little effect on the power dissipation of the display and
is not considered when determining the power dissipation.
Power Deration Curve
(θ
ja
=50°C/W)
2.5
IDDG5333
P
W
2.0
1.5
1.0
0.5
0
-40
-20
0
20
40
60
˚C 100
T
V
CC
and
V
LL
are two separate power supplies sharing a common
ground.
V
CC
supplies power for all the display logic.
V
LL
supplies
the power for the LEDs. By separating the two supplies,
V
CC
and
V
LL
can be varied independently and keeps the logic supply clean.
2006-01-23
10
OSRAM [ OSRAM GMBH ]
