LM3915N-1 National Semiconductor, LM3915N-1 Datasheet - Page 12

• Manufacturer Part Number: LM3915N-1
• Description: IC, DOT/BAR DISPLAY DRIVER, DIP-18
• Manufacturer: National Semiconductor

Specifications of LM3915N-1

• Led Driver Application: VU Meter, Power Meters
• No. Of Outputs: 10
• Output Current: 30mA
• Input Voltage: 3V To 25V
• Dimming Control Type: Analog
• Operating Temperature Range: 0°C To +70°C
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

www.national.com
Application Hints
in both the precision rectifier and the 30 dB gain stage.
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
lowest LM3915 displays input signals down to 0.5 mV! Sev-
eral 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.
(Continued)
FIGURE 5. Low Cost Circuit for 60 dB Display
FIGURE 6. Improved Circuit for 60 dB Display
12
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.
TIPS ON REFERENCE VOLTAGE
AND LED CURRENT PROGRAMMING
Single LM3915
The equations in Figure 7 illustrate how to choose resistor
values to set reference voltage for the simple case where no
LED intensity adjustment is required. A LED current of 10 mA
to 20 mA generally produces adequate illumination. Having
10V full-scale across the internal voltage divider gives best
accuracy by keeping signal level high relative to the offset
voltage of the internal comparators. However, this causes
450 µA to flow from pin 7 into the divider which means that
00510414
00510413