LM3915MWC National Semiconductor Corporation, LM3915MWC Datasheet - Page 13

• Manufacturer Part Number: LM3915MWC
• Description: Dot/bar Display Driver
• Manufacturer: National Semiconductor Corporation

Application Hints
The scheme in Figure 10 is useful when the reference and
LED intensity must be adjusted independently over a wide
range. The R
with no effect on LED current. Since the internal divider here
does not load down the reference, minimum LED current is
much lower. At the minimum recommended reference load
of 80 µA, LED current is about 0.8 mA. The resistor values
shown give a LED current range from 1.5 mA to 20 mA.
At the low end of the intensity adjustment, the voltage drop
across the 510
chip to chip variation in reference voltage may yield a visible
variation in LED intensity. The optional approach shown of
connecting the bottom end of the intensity control pot to a
negative supply overcomes this problem by allowing a larger
voltage drop across the (larger) current-sharing resistors.
FIGURE 9. Independent Adjustment of Reference Voltage and LED Intensity for Multiple LM3915s
HI
voltage can be adjusted from 1.2V to 10V
current-sharing resistors is so small that
(Continued)
13
Other Applications
For increased resolution, it’s possible to obtain a display with
a smooth transition between LEDs. This is accomplished by
varying the reference level at pin 6 by 3 dBp-p as shown in
Figure 11 . The signal can be a triangle, sawtooth or sine
wave from 60 Hz to 1 kHz. The display can be run in either
dot or bar mode.
When an exponentially decaying RC discharge waveform is
applied to pin 5, the LM3915’s outputs will switch at equal
intervals. This makes a simple timer or sequencer. Each time
interval is equal to RC/3. The output may be used to drive
logic, opto-couplers, relays or PNP transistors, for example.
DS005104-17
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