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PDF LM3916 Data sheet ( Hoja de datos )
| Número de pieza | LM3916 | |
| Descripción | Dot/Bar Display Driver | |
| Fabricantes | National Semiconductor | |
| Logotipo |  |
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January 2000
LM3916
Dot/Bar Display Driver
General Description
The LM3916 is a monolithic integrated circuit that senses
analog voltage levels and drives ten LEDs, LCDs or vacuum
fluorescent displays, providing an electronic version of the
popular VU meter. One pin changes the display from a bar
graph to a moving dot display. LED current drive is regulated
and programmable, eliminating the need for current limiting
resistors. The whole display system can operate from a
single supply as low as 3V or as high as 25V.
The IC contains an adjustable voltage reference and an ac-
curate ten-step voltage divider. The high-impedance input
buffer accepts signals down to ground and up to within 1.5V
of the positive supply. Further, it needs no protection against
inputs of ±35V. The input buffer drives 10 individual com-
parators referenced to the precision divider. Accuracy is typi-
cally better than 0.2 dB.
Audio applications include average or peak level indicators,
and power meters. Replacing conventional meters with an
LED bar graph results in a faster responding, more rugged
display with high visibility that retains the ease of interpreta-
tion of an analog display.
The LM3916 is extremely easy to apply. A 1.2V full-scale
meter requires only one resistor in addition to the ten LEDs.
One more resistor programs the full-scale anywhere from
1.2V to 12V independent of supply voltage. LED brightness
is easily controlled with a single pot.
The LM3916 is very versatile. The outputs can drive LCDs,
vacuum fluorescents and incandescent bulbs as well as
LEDs of any color. Multiple devices can be cascaded for a
dot or bar mode display for increased range and/or resolu-
tion. Useful in other applications are the linear LM3914 and
the logarithmic LM3915.
Features
n Fast responding electronic VU meter
n Drivers LEDs, LCDs, or vacuum fluorescents
n Bar or dot display mode externally selectable by user
n Expandable to displays of 70 dB
n Internal voltage reference from 1.2V to 12V
n Operates with single supply of 3V to 25V
n Inputs operate down to ground
n Output current programmable from 1 mA to 30 mA
n Input withstands ±35V without damage or false outputs
n Outputs are current regulated, open collectors
n Directly drives TTL or CMOS
n The internal 10-step divider is floating and can be
referenced to a wide range of voltages
The LM3916 is rated for operation from 0˚C to +70˚C. The
LM3916N-1 is available in an 18-lead molded DIP package.
© 2000 National Semiconductor Corporation DS007971
www.national.com
1 page  
Typical Performance Characteristics (Continued)
Reference Adjust Pin
Current vs Temperature
LED Current-Regulation
Dropout
LED Driver Saturation
Voltage
DS007971-38
Input Current Beyond
Signal Range (Pin 5)
DS007971-39
LED Current vs
Referenced Loading
LED Driver Current
Regulation
DS007971-40
DS007971-41
DS007971-42
Total Divider Resistance
vs Temperature
Common-Mode Limits
DS007971-43
Output Characteristics
DS007971-44
DS007971-45
DS007971-46
5 www.national.com
5 Page 
Application Hints (Continued)
Design Equations
DS007971-14
GAIN
1
10
R5 R6 C2
C3
100k 43k 2.0 0.56 µF
1M 100k 1.0 0.056 µF
FIGURE 7. Full-Wave Average Detector to VU Meter Specifications*
Peak Program Meter
Cascading The LM3916
The VU meter, originally intended for signals sent via tele-
phone lines, has shortcomings when used in high fidelity
systems. Due to its slow response time, a VU meter will not
accurately display transients that can saturate a magnetic
tape or drive an amplifier into clipping. The fast-attack peak
program meter (PPM) which does not have this problem is
becoming increasingly popular.
While several European organizations have specifications
for peak program meters, the German DIN specification
45406 is becoming a de facto standard. Rather than respond
instantaneously to peak, however, PPM specifications re-
quire a finite “integration time” so that only peaks wide
enough to be audible are displayed. DIN 45406 calls for a re-
sponse of 1 dB down from steady-state for a 10 ms tone
burst and 4 dB down for a 3 ms tone burst. These require-
ments are consistent with the other frequently encountered
spec of 2 dB down for a 5 ms burst and are met by an attack
time constant of 1.7 ms.
The specified return time of 1.5s to −20 dB requires a
650 ms decay time constant. The full-wave peak detector of
Figure 6 satisfies both the attack and decay time criteria.
The LM3916 by itself covers the 23 dB range of the conven-
tional VU meter. To display signals of 40 dB or 70 dB dy-
namic range, the LM3916 may be cascaded with the 3 dB/
step LM3915s. Alternatively, two LM3916s may be cascaded
for increased resolution over a 28 dB range. Refer to the Ex-
tended Range VU Meter and High Resolution VU Meter in
the Typical Applications section for the complete circuits for
both dot and bar mode displays.
To obtain a display that makes sense when an LM3915 and
an LM3916 are cascaded, the −20 dB output from the
LM3916 is dropped. The full-scale display for the LM3915 is
set at 3 dB below the LM3916’s −10 dB output and the rest
of the thresholds continue the 3 dB/step spacing. A simple,
low cost approach is to set the reference voltage of the two
chips 16 dB apart as in Figure 5. The LM3915, with pin 8
grounded, runs at 1.25V full-scale. R1 and R2 set the
LM3916’s reference 16 dB higher or 7.89V. Variation in the
two on-chip references and resistor tolerance may cause a
±1 dB error in the −10 dB to −13 dB transition. If this is ob-
jectionable, R2 can be trimmed.
The drawback of the aforementioned approach is that the
threshold of LED #1 on the LM3915 is only 56 mV. Since
comparator offset voltage may be as high as 10 mV, large er-
rors can occur at the first few thresholds. A better approach,
as shown in Figure 9, is to keep the reference the same for
11 www.national.com
11 Page | ||
| Páginas | Total 27 Páginas | |
| PDF Descargar | [ Datasheet LM3916.PDF ] | |
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