HCMS-39X2 HP [Agilent(Hewlett-Packard)], HCMS-39X2 Datasheet - Page 19

• Manufacturer Part Number: HCMS-39X2
• Description: 3.3 V High Performance CMOS 5x7 AlphaNumeric Displays
• Manufacturer: HP [Agilent(Hewlett-Packard)]

19
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 in Table 3.
Table 3. Equations.
Equation 1:
T
Where: T
Equation 2:
P
Where:
Equation 3:
I
Where:
Equation 4:
I
(See Variable Definitions above)
PEAK
LED
J
D
MAX = T
= (N * I
(AVG) = N * I
Duty Factor = 1/8 * Osccyc/64
= M * 20 * I
Osc cyc = number of ON oscillator cycles per row
J
V
PIXEL
I
I
I
I
LOGIC
LOGIC
A
MAX = maximum IC junction temperature
R
PIXEL
PIXEL
PEAK
+ P
P
P
T
JA
20 = maximum number of LEDs on per IC
M = number of ICs in the system
N = number of pixels on (maximum 4 char * 5 * 7 = 140)
A
D
D
* Duty Factor * V
D
= ambient temperature surrounding the display
= thermal resistance from the IC junction to ambient
= total power dissipation
= total power dissipation
= peak pixel current.
= IC logic current
= logic supply voltage
PIXEL
= maximum instantaneous peak current for the display
= peak current for one LED
PIXEL
* R
* 1/8 * (oscillator cycles)/64
JA
LED
) + I
The average current required by
the display can be calculated with
Equation 4 in Table 3.
The power supply has to be able
to supply I
supply I
The range on V
on this supply without signifi-
cantly changing the display
brightness.
LOGIC
* V
LED
LOGIC
PEAK
(AVG) continuously.
LED
transients and
allows noise
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
dependently. Thus, V
from 0 to 5.5 V without affecting
either the Dot or the Control
Registers. V
between 3.1 to 5.5 V without
much noticeable variation in light
output to the human eyes. There
is also no pixel mismatch
observed.
The intensity of the light output
takes a plunge if operated less
than 3.1 V. There is also no pixel
mismatch observed at voltage as
low as 2.6 V. However, operating
below 3.1 V is not recommended.
Dimming the display by pulse
width modulating V
recommended.
V
without affecting either the
displayed message or the display
intensity. However, operating
below 3 V may change the timing
and logic levels and may cause
Dot and Control Registers to be
altered. Thus, operation of the
display below 3.0 V is not
recommended.
LOGIC
LOGIC
LOGIC
and V
to be varied in-
can vary from 3.0 to 5.5 V
LED
LED
Considerations
can be varied
LED
LED
LED
is also not
can vary
and