HCMS-xxxx Hewlett-Packard, HCMS-xxxx Datasheet - Page 14

• Manufacturer Part Number: HCMS-xxxx
• Description: High Performance CMOS 5 x 7 Alphanumeric Displays
• Manufacturer: Hewlett-Packard

Appendix A. Thermal
Considerations
The display IC has a maximum
junction temperature of 150 C.
The IC junction temperature can
be calculated with Equation 1
below.
A typical value for R
W. This value is typical for a
display mounted in a socket and
covered with a plastic filter. The
socket is soldered to a .062 in.
thick PCB with .020 inch wide,
one ounce copper traces.
Equation 1:
T
Where:
Equation 2:
P
Where:
Equation 3:
I
Where:
Equation 4:
I
(see Variable Definitions above)
Duty Factor = 1/8 * Osccyc/64
PEAK
LED
J
D
MAX = T
= (N * I
(AVG) = N * I
Osc cyc = number of ON oscillator cycles per row
T
= M * 20 * I
I
I
V
PIXEL
J
I
PEAK
I
MAX = maximum IC junction temperature
LOGIC
LOGIC
PIXEL
R
20 = maximum number of LEDs on per IC
M = number of ICs in the system
P
P
T
JA
N = number of pixels on (maximum 4 char * 5 * 7 = 140)
A
D
D
A
PIXEL
= maximum instantaneous peak current for the display
= peak current for one LED
+ P
= ambient temperature surrounding the display
= thermal resistance from the IC junction to ambient
= power dissipated by the IC
= total power dissipation
= peak pixel current.
= IC logic current
= logic supply voltage
* Duty Factor * V
D
PIXEL
PIXEL
* R
JA
is 100 C/
JA
* 1/8 * (oscillator cycles)/64
LED
P
2 below.
Figure 4 shows how to derate the
power of one IC versus ambient
temperature. Operation at high
ambient temperatures may
require the power per IC to be
reduced. The power consumption
can be reduced by changing
either the N, I
V
little impact on the power
consumption.
) + I
LED
D
can be calculated as Equation
. Changing V
LOGIC
* V
LOGIC
PIXEL
LOGIC
, Osc cyc or
has very
14
Figure 4.
Appendix B. Electrical
Considerations
Current Calculations
The peak and average display
current requirements have a
significant impact on power
supply selection. The maximum
peak current is calculated with
Equation 3 below.
The average current required by
the display can be calculated with
Equation 4 below.
The power supply has to be able
to supply I
supply I
The range on V
this supply without significantly
changing the display brightness.
V
The display uses two independent
electrical systems. One system is
used to power the display’s logic
and the other to power the
display’s LEDs. These two
systems keep the logic supply
clean.
Separate electrical systems allow
the voltage applied to V
V
Thus, V
V without affecting either the Dot
or the Control Registers. V
LOGIC
LOGIC
1.3
1.2
1.1
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
to be varied independently.
and V
LED
25
LED
30
T
PEAK
(AVG) continuously.
can vary from 0 to 5.5
35
A
– AMBIENT TEMPERATURE – °C
LED
40
LED
transients and
45
Considerations
50
allows noise on
55
R
60
J-A
LED
65
= 100°C/W
70
LED
and
75
80
can
85
90