LM3915N National Semiconductor, LM3915N Datasheet - Page 9

• Manufacturer Part Number: LM3915N
• Description: IC DRIVER DOT BAR DISPLAY 18-DIP
• Manufacturer: National Semiconductor

Specifications of LM3915N

• Display Type: LED, LCD, Vacuum Fluorescent
• Configuration: Dot/Bar Display
• Digits Or Characters: 10 Steps
• Current - Supply: 6.1mA
• Voltage - Supply: 3 V ~ 25 V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Through Hole
• Package / Case: 18-DIP (0.300", 7.62mm)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Interface: -
• Other names: *LM3915N; LM3915

Application Hints
CASCADING THE LM3915
To display signals of 60 or 90 dB dynamic range multiple
LM3915s can be easily cascaded Alternatively it is possi-
ble to cascade an LM3915 with LM3914s for a log linear
display or with an LM3916 to get an extended range VU
meter
A simple low cost approach to cascading two LM3915s is
to set the reference voltages of the two chips 30 dB apart
as in Figure 5 Potentiometer R1 is used to adjust the full
scale voltage of LM3915
second IC’s reference is set at 10V by R4 The drawback of
this method is that the threshold of LED
and since the LM3915 can have an offset voltage as high
as 10 mV large errors can occur This technique is not rec-
ommended for 60 dB displays requiring good accuracy at
the first few display thresholds
A better approach shown in Figure 6 is to keep the refer-
ence at 10V for both LM3915s and amplify the input signal
1 to 316 mV nominally while the
(Continued)
FIGURE 4 Precision Full-Wave Peak Detector
FIGURE 5 Low Cost Circuit for 60 dB Display
1 is only 14 mV
9
D1 D2 D3 D4 1N914 or 1N4148
to the lower LM3915 by 30 dB Since two 1% resistors can
set the amplifier gain within
sary However an op amp offset voltage of 5 mV will shift
the first LED threshold as much as 4 dB so that an offset
trim may be required Note that a single adjustment can null
out offset in both the precision rectifier and the 30 dB gain
stage Alternatively instead of amplifying input signals of
sufficient amplitude can be fed directly to the lower LM3915
and attenuated by 30 dB to drive the second LM3915
To extend this approach to get a 90 dB display another 30
dB of amplification must be placed in the signal path ahead
of the lowest LM3915 Extreme care is required as the low-
est LM3915 displays input signals down to 0 5 mV Several
offset nulls may be required High currents should not share
the same path as the low level signal Also power line wiring
should be kept away from signal lines
g
0 2 dB a gain trim is unneces-
TL H 5104 – 12
TL H 5104 – 13