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PDF DM9374 Data sheet ( Hoja de datos )
| Número de pieza | DM9374 | |
| Descripción | 7-Segment Decoder/Driver/Latch | |
| Fabricantes | National Semiconductor | |
| Logotipo |  |
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DM9374 7-Segment Decoder Driver Latch
with Constant Current Sink Outputs
General Description
The ’74 is a 7-segment decoder driver incorporating input
latches and output circuits to directly drive common anode
LED displays
Connection Diagram
Logic Symbol
Dual-In-Line Package
June 1989
TL F 10210 – 1
Order Number DM9374N
See NS Package Number N16E
VCC e Pin 16
GND e Pin 8
Pin
Names
A0 – A3
LE
RBI
RBO
a–g
Description
Address (Data Inputs)
Latch Enable Input (Active LOW)
Ripple Blanking Input (Active LOW)
Ripple Blanking as Output (Active LOW)
as Input (Active LOW)
Constant Current Outputs (Active LOW)
TL F 10210 – 2
C1995 National Semiconductor Corporation TL F 10210
RRD-B30M105 Printed in U S A
http://www.Datasheet4U.com
1 page  
Applications
It is possible with common anode 7-segment LED displays
and constant current sink decoder drivers to save substan-
tial amounts of power by carefully choosing operating points
on display supply voltage First examine the power used in
the normal display driving method where the display and
decoder driver are both operated from a a5 0V regulated
supply (VCC e VS)
The power dissipated by the LED and the driver outputs is
(VCC x Iseg x n Segments) The total power dissipated with a
15 mA LED displaying an eight (8) would be
PTOT e 5 0V x 15 mA x 7
e 525 mW
Of this 525 mW the power actually required to drive the
LED is dependent on the VF drop of each segment Most
GaAsP LEDs exhibit either a 1 7V or a 3 4V forward voltage
drop Therefore the required total power for seven seg-
ments would be
P(1 7) e 1 7V x 15 mA x 7
e 178 5 mW
P(3 4) e 3 4V x 15 mA x 7
e 357 mW
The remaining power is dissipated by the driver outputs
which are maintaining the 15 mA constant current required
by the LEDs Most of this power is wasted since the driver
can maintain approximately 15 mA with as little as 0 5V
across the output device By using a separate power source
(VS Figure C ) for the LEDs which is set to the LED VF plus
the offset voltage of the driver as much as 280 mW can be
saved per digit i e
VS e VF (Max) a Voffset
e 2 0V a 0 5V
e 2 5V
PT e 2 5V x 14 mA (from Figure B ) x 7
e 245 mW
These figures show that using a separate supply to drive the
LEDs can offer significant display power savings In battery
powered equipment two rechargeable nickle-cadmium cells
in series would be sufficient to drive the display while four
such cells would be needed to operate the logic units
Another method to save power is to apply intensity modula-
tion to the displays (Figure D) It is well known that LED
displays are more efficient when operated in pulse mode
There are two reasons one the quantum efficiency of the
LED material is better secondly the eye tends to peak de-
tect Typically a 20% off duty cycle to displays (GaAsP) will
produce the same brightness as operating under dc condi-
tions
FIGURE C Separate Supply for LED Displays
TL F 10210 – 11
5
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| Páginas | Total 8 Páginas | |
| PDF Descargar | [ Datasheet DM9374.PDF ] | |
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